EXAMINATION QUESTIONS FOR RATES OF REACTION
A fixed mass of marble is reacted with dilute hydrochloric acid at a constant temperature. Explain why the rate of the reaction is increased if the lumps of marble are reduced in size.
1.
.......................................................... ........................................................................................ .............................................................. ............................................. ............. .......................................................... ........................................................................................ .............................................................. ............................................. ............. .......................................................... ........................................................................................ .............................................................. ............................................. ............. (2)
(Total 2 marks)
(c)
Hydrog Hydrogen en peroxi peroxide de decom decompose posess more rapi rapidly dly in the the presenc presencee of aqueou aqueouss hydroge hydrogen n bromide. The decomposition decomposition proceeds as shown by the following equations. H! " H#r
→
H#r! " H!
H#r! " H ! → H! " ! " H#r (i) (i)
$rite $r ite an equa equatio tion n for for the the o%e o%era rall ll reac reacti tion on.. ......................................................... ........................................................................................& ...............................&.............................. ................................
(ii)
'efine ine the term catalyst . ......................................................... ........................................................................................& ...............................&.............................. ................................ ......................................................... ........................................................................................& ...............................&.............................. ................................
(iii)
i%e two reasons other than an increase in the reaction rate why these equations suggest that hydrogen bromide is beha%ing as a catalyst. Reason 1 ......................................................... ......................................................................................... ................................................... ................... Reason 2 ......................................................... ......................................................................................... ................................................... ................... (5) (Total 10 marks)
2.
as decomposes as shown in i n the equation below. (g) → *(g) " +(g)
(a)
'raw 'raw on the axes axes below below a ,axwel ,axwell-# l-#olt oltzma zmann nn distri distribut bution ion cur%e cur%e for for a sample sample of in which only a small proportion of molecules has energy greater than the acti%ation energy E a.
. u m b e r o f m o le c u le s
Energy
E a
(!)
(b)
'efine the term activation energy. energy. .....................&&&&&&&&&&&&&&&&&&&&&&&&&&&&. .....................&&&&&&&&&&&&&&&&&&&&&&&&&&&&. (2)
(c) (c)
At any any tim time e most most of of the the mole molecu cule less of of ha%e energy less than the acti%ation energy. /uggest why at a constant temperature most of e%entually decomposes. .....................&&&&&&&&&&&&&&&&&&&&&&&&&&&&. .....................&&&&&&&&&&&&&&&&&&&&&&&&&&&&. (2)
(d)
/tate /tate the the effect effect if any any of addi adding ng a cata catalys lystt on the the time time requir required ed for for to decompose compared with a similar sample without a catalyst. Explain in general terms how the catalyst has this effect. Time for decomposition &&........................................................ &&...................................................................................... .............................. Explanation &&&&&&&&&&&&&&&&&&&&&&&&&&&&. .....................&&&&&&&&&&&&&&&&&&&&&&&&&&&&. (!) (Total 10 marks)
!.
(a)
#elow is a ,axwell-#ol ,axwell-#oltzman tzmann n cur%e cur%e showing showing the the distribu distribution tion of molecular molecular energies energies for a sample of gas at a temperature T .
(i) (i)
0abe 0abell the the axes axes on the the dia diagr gram am abo% abo%e. e.
(ii) (ii)
$hat $hat doe doess the the area area und under er the the cur cur%e %e rep repre rese sent nt11 ......................................................... ......................................................................................... ............................................................. .............................
(iii) (iii)
/tate /tate why why this this cur%e cur%e starts starts at the the origin origin.. ......................................................... ......................................................................................... ............................................................. ............................. (")
(b)
(i)
/tate what is meant by the term activation energy. energy . ......................................................... ......................................................................................... ............................................................. ............................. ......................................................... ......................................................................................... ............................................................. .............................
(ii) (ii)
The rate rate of of a chemica chemicall reactio reaction n may be be increas increased ed by an incr increas easee in reacta reactant nt concentration by an increase in temperature and by the addition of a catalyst. /tate which if any an y of of these changes in%ol%es a different acti%ation energy. Explain Explain your answer. Change(s) ........................................................... ........................................................................................... .......................................... .......... Explanation .............................................................. ............................................................................................ .................................... ...... ......................................................... ......................................................................................... ............................................................. ............................. (5) (Total # marks)
(Total $ marks)
".
The diagram below represents a ,axwell-#oltzmann distribution cur%e for the particles in a sample of a gas at a gi%en temperature. The questions below refer to this sample of particles.
(a) (a)
0abe 0abell the the axes axes on the the dia diagr gram am.. (2)
(b)
!n the the diagra diagram m draw draw a cur%e cur%e to to show show the dist distribu ribution tion for this this samp sample le at a low%r temperature. (2)
(c)
2n order order for two particl particles es to react they must collide collide.. Explain Explain why most collisions collisions do not not result in a reaction. .......................................................... ........................................................................................ .............................................................. ............................................. ............. (1)
(d)
/tate /tate one way way in which which the the collisi collision on frequ frequency ency betwee between n partic particles les in a gas gas can be be increased without changing the temperature. .......................................................... ........................................................................................ .............................................................. ............................................. ............. (1)
(e)
/uggest /uggest why why a small small increa increase se in temper temperatu ature re can can lead to to a large large incre increase ase in the the react reaction ion rate between colliding particles. .......................................................... ........................................................................................ .............................................................. ............................................. ............. .......................................................... ........................................................................................ .............................................................. ............................................. ............. .......................................................... ........................................................................................ .............................................................. ............................................. ............. (2)
(f) (f)
Expl Explai ain n in in gen gener eral al term termss how how a cata cataly lyst st wor wor3s 3s.. .......................................................... ........................................................................................ .............................................................. ............................................. ............. .......................................................... ........................................................................................ .............................................................. ............................................. ............. .......................................................... ........................................................................................ .............................................................. ............................................. ............. (2) (Total 10 marks)
5.
(a) (a)
/tat /tatee wha whatt is is mea meant nt by the the ter term m activation energy of a reaction. (1)
(b)
/tate /tate in gener general al terms terms how how a catalys catalystt increas increases es the rate rate of of a chemical chemical reac reactio tion. n. (2)
(c)
The cur%e below shows the ,axwell-#o ,axwell-#oltzmann ltzmann distribution distribution of molecular molecular energies energies at a constant temperature in a gas at the start of a reaction. !n this diagram the most probable molecular energy at this temperature is indicated by the symbol E mp and the acti%ation energy by the symbol E symbol E a.
. u m b e r o f m o le c u le s
E m p
E a
Energy
4onsider the following changes. (i)
The number number of molecu molecules les is increa increased sed at constan constantt tempe temperat rature ure..
(ii) (ii)
The temp tempera eratur turee is decrea decreased sed witho without ut chang changing ing the the number number of mole molecul cules. es.
(iii)
A cataly catalyst st is introduc introduced ed without without changin changing g the temper temperature ature or the number number of molecules.
5or %a&' of these changes state how if at all the following would %ary6 •
the %alue of the most probable energy E energy E mp
•
the number of molecules with the most probable energy E energy E mp
•
the area under the molecular energy distribution cur%e
•
the number of molecules with energy greater than the acti%ation energy E energy E a (12) (Total 15 marks)
.
(a )
'efine th the te term activation energy for a chemical reaction. (2)
(b)
'raw 'raw with labelle labelled d axes axes a cur%e cur%e to represent represent the ,axwell,axwell-#oltzm #oltzmann ann distrib distribution ution of molecular energies in a gas. 0abel this cur%e T7. !n the same axes draw a second cur%e to represent the same sample of gas at a l ower temperature. 0abel this cur%e T. 8se these cur%es to explain why a small decrease in temperature can lead to a large decrease in the rate of a reaction. ($)
(c )
i%e o% reason why most collisions between gas9phase reactants do not lead to a reaction. /tate and explain two ways of speeding up a gas9phase reaction other than by changing the temperature. (5) (Total 15 marks)
*.
'raw a ,axwell9#oltzman cur%e for a sample of gas at a te mperature T 7. !n the same axes draw a second cur%e for the same sample of gas at a higher temperature T . 0abel the cur%es and the axes clearly. Explain using these cur%es wh y an increase in te mperature increases the rate of a gas phase reaction. /uggest how and why the first cur%e would change if a larger mass of gas were used at temperature T 7. (Total 10 marks)
$.
(a)
A sample sample of a gas gas was was seale sealed d into into a flas3 flas3 at at temp tempera erature ture T and pressure P pressure P . The ,axwell- #oltzmann distribution of energies for the molecules in this sample is shown below.
. u m b e r o f m o l e cu le s
Energy
(i)
8sing 8sing the the axes axes abo%e abo%e s3etch s3etch the the cur% cur%ee that that you you would would expe expect ct if this this sample sample of of gas at pressure P pressure P had been cooled. 0abel this cur%e X.
(ii) (ii)
8sing 8sing the axes axes abo%e abo%e s3etch s3etch the the cur%e cur%e that that you woul would d expect expect if anot another her samp sample le of the same gas was sealed in the same s ame flas3 at the original temperature T but at a higher pressure. 0abel this cur%e +. (")
(b)
as A decomposes slowly to form gases , and C. An equilibrium is established as s hown by the following equation. A(g)
(i)
#(g) " 4(g)
∆ H
is positi%e
2n terms terms of of the beha beha%io %iour ur of mole molecul cules es stat statee what what must must happen happen befo before re molec molecule uless of A can react to form , and C. ......................................................... ......................................................................................... .............................................................. .................................. .... ......................................................... ......................................................................................... .............................................................. .................................. ....
(ii) (ii)
Expl Explai ain n why the the decom decompo posit sition ion of A is faster at higher temperatures. ......................................................... ......................................................................................... .............................................................. .................................. .... ......................................................... ......................................................................................... .............................................................. .................................. .... (")
(c) (c)
The The gra graph phss belo below w show show how how star starti ting ng from from A alone the concentration of A %aries with time at temperatures of :;; < and :; < for the re%ersible reaction gi%en in part (b).
4 o n c e n t ra tio n of A :;; < :; <
T im e
(i)
/ugges /uggestt why why as shown shown on the graphs graphs the the concen concentra tratio tion n of of A remains constant after a time. ......................................................... ......................................................................................... .............................................................. .................................. ....
(ii) (ii)
Expl Explai ain n why why at at :; :; < the the con conce cent ntra rati tion on of of A falls to a lower %alue compared with the reaction at :;; <. ......................................................... ......................................................................................... .............................................................. .................................. .... ......................................................... ......................................................................................... .............................................................. .................................. .... ......................................................... ......................................................................................... .............................................................. .................................. .... (!) (Total 11 marks)
#.
(a)
The diag diagram ram below below shows shows the the distrib distributi ution on cur%e cur%e for for the ener energie giess of molec molecule uless in a gi%en gi%en mass of methane.
. u m b e r o f m o le c u le s w ith a g i % e n energy
Energy
(i)
2f the the graph graph were were exten extended ded to to higher higher ener energie gies s at what what poin pointt would would the the cur%e cur%e meet meet the horizontal axis1 Explain your answer. Point .............................................................. ............................................................................................ .................................................... ...................... Explanation........................... Explanation......................................................... ............................................................ .............................................. ................ ......................................................... ......................................................................................... .............................................................. .................................. .... ......................................................... ......................................................................................... .............................................................. .................................. ....
(ii) (ii)
/3etch /3etch on on the diag diagram ram a cur% cur%ee for a large largerr mass mass of metha methane ne at the the same same temperature.
(iii)
A sample sample of of ethane ethane containin containing g the same same number number of moles moles as the the sample sample of methane methane abo%e is at the same same temperature and pressure. pressure. 'escribe how the distribution distribution cur%e for ethane differs if at all from that abo%e. ......................................................... ......................................................................................... .............................................................. ................................. ... ......................................................... ......................................................................................... .............................................................. ................................. ... (5)
(b)
i%e i%e two requi requirem rement entss for a reactio reaction n to occur occur betwe between en two gaseo gaseous us molecu molecules. les. Reqirement 1......................... 1....................................................... .............................................................. ...................................................... ...................... Reqirement 2......................... 2....................................................... .............................................................. ...................................................... ...................... (2) (Total * marks)
10.
,ethanol can be formed on an industrial scale from carbon dioxide and hydrogen by a re%ersible reaction as shown below. 4!(g) " :H (g)
4H:!H(g) " H!(g)
The reaction can be carried out in the presence of a chromium9based catalyst at a temperature of =;; < and a pressure of :; ,>a. 8nder these conditions equilibrium is reached when ? of the carbon dioxide has been con%erted.
(a)
How does does the rate rate of the the forwa forward rd react reaction ion comp compare are with with that that of the the bac3war bac3ward d reacti reaction on when ? of the carbon dioxide has been con%erted1 .....................&&&&&&&&&&&&&&&&&&&&&&&&&&&&. (1)
(b) (b)
(i) (i)
2f the the pre pressu ssure re was was red reduc uced ed but but the the tempe tempera ratu ture re was was 3ep 3eptt the the same same dedu deduce ce what what would happen to the equilibrium yield of methanol. Explain your answer. !ield &&.&&&&&&&&&&&&&&&&&&&&&&&&&&. Explanation ..&&&&&&&&&&&&&&&&&&&&&&&&&. ...........&&&&&&&&&&&&&&&&&&&&&&&&&&&&.
(ii)
i%e two reasons reasons why why in in general general industry industry prefers prefers to operate operate proces processes ses at pressures pressures lower than :; ,>a. Reason 1 1 &..&&&&&&&&&&&&&&&&&&&&&&&&&. Reason 2 2 &..&&&&&&&&&&&&&&&&&&&&&&&&&. (5)
(c)
2f the chrom chromium ium9ba 9based sed cataly catalyst st was replace replaced d with a more more efficie efficient nt cataly catalyst st but other other conditions were 3ept the same deduce what would happen to the equilibrium yield of methanol. Explain your answer. !ield &&.&&&&&&&&&&&&&&&&&&.&.&&&&&&&&&. Explanation ..&&&&&&&&&&&.&&&&&.&&&&&&&&&&&. .....................&&&&&&&&&&&&&&&&&&&&&&&&&&&&. (2)
(d)
2n the the presence presence of a %ery efficient efficient copper9b copper9based ased cataly catalyst st this this industrial industrial process process can be operated at a lower temperature of @;; < and a pressure of :; ,>a. 8nder these conditions at equilibrium more of the carbon dioxide is con%erted into methanol. 8se this information to deduce the sign of the enthalpy change for the reaction. Explain your deduction. "ign of enthalpy change###$...................................................................&&&& change###$ ...................................................................&&&& Explanation #$&&&&&&&&&&&&&&&&&&&&&&&&&&&. #$&&&&&&&&&&&&&&&&&&&&&&&&&&&. .....................&&&&&&&&&&&&&&&&&&&&&&&&&&&&. (!)
(e)
2n the the process processes es abo%e abo%e the equilibrium equilibrium yield of methano methanoll is low. low. /uggest /uggest what what is done
with the unreacted carbon dioxide and hydrogen. .....................&&&&&&&&&&&&&&&&&&&&&&&&&&&&. (1) (Total 12 marks)
11.
(a)
The diag diagram ram below below shows shows the the ,axwell9 ,axwell9#ol #oltzm tzmann ann energ energy y distrib distributi ution on cur%es cur%es for for molecules of a sample of a gas at two different temperatures.
A
#
4
'
(i)
0abel both axes.
(ii) (ii)
4hoose 4hoose one one of the the letters letters on on the axes axes abo%e abo%e which which repre represen sents ts the most most proba probable ble energy of the molecules at the lower temperature. ......................................................... ......................................................................................... .............................................................. ................................... ..... (!)
(b)
i%e i%e two requi requirem rement entss for a reactio reaction n to occur occur betwe between en molec molecule uless in the gas gas phase. phase. Reqirement 1 ............................................................ .......................................................................................... ................................................ .................. Reqirement 2 ............................................................ .......................................................................................... ................................................ .................. (2)
(c)
$hich $hich has has the greate greaterr effec effectt on the the initia initiall rate rate of a first first9or 9order der reac reaction tion66 %-t'%r increasing the temperature of the reaction mixture from :;; < to :; < (a :? increase) or
increasing the concentration of the reagent from 7.;; , to 7.;: , (also a :? increase)1
#riefly explain your answer. %reater effect ............................. effect ........................................................... ............................................................ ................................................... ..................... Explanation ......................................................... ....................................................................................... ........................................................ .......................... .......................................................... ........................................................................................ .............................................................. ............................................ ............ .......................................................... ........................................................................................ .............................................................. ............................................ ............ (!) (Total $ marks)
12.
At high temperatures nitrogen is oxidised by oxygen to form nitrogen monoxide in a re%ersible reaction as shown in the equation below. (g) " !(g)
(b)
!(g)
C -7 B H D "7; 3F mol
/tate and explain explain the effect effect of an increase increase in pressure pressure and and the effect effect of an increase increase in temperature on the yield of nitrogen monoxide in the abo%e equilibrium. Effect of an increase in pressre pressre on the yield yield ............................................................. Explanation ......................................................... ....................................................................................... ........................................................ .......................... .......................................................... ........................................................................................ .............................................................. ............................................. ............. .......................................................... ........................................................................................ .............................................................. ............................................. ............. .......................................................... ........................................................................................ .............................................................. ............................................. ............. Effect of an increase in temperatre temperatre on the yield ....................................................... Explanation ......................................................... ....................................................................................... ........................................................ .......................... .......................................................... ........................................................................................ .............................................................. ............................................. ............. .......................................................... ........................................................................................ .............................................................. ............................................. ............. ()
(Total marks)
1!.
/ulphur dioxide and oxygen were mixed in a 67 mol ratio and sealed in a flas3 with a catalyst. The following equilibrium was established at temperature T 7 /!(g) " ! (g)
(e)
/!:(g)
∆ H
&
-7
-7G 3F mol
2n a further further experiment experiment the amounts amounts of of sulphur sulphur dioxide dioxide and oxygen oxygen used the the catalyst catalyst and and the temperature T 7 were all unchanged but a flas3 of smaller %olume was used. 'educe the effect of this change on the yield of sulphur trioxide and on the %alue of ' p. Effect on yield of " ............................................................ ....................................................................&....................... ........&............................ ..... Effect on ' p .............................................................. ............................................................................................ ...................................................... ........................ (2)
1".
Hydrogen is produced on an industrial scale from methane as shown by the equation below. 4H(g) " H !(g) (a) (a)
4!(g) " :H(g)
∆ H
-7
D ";@ 3F mol
/tat /tatee 0e 0e 4ha 4hate teli lier erIIs pri princ ncip iple le.. .......................................................... ........................................................................................ .............................................................. ............................................. ............. .......................................................... ........................................................................................ .............................................................. ............................................. ............. (1)
(b)
The following following changes changes are are made made to this reaction reaction at at equilibriu equilibrium. m. 2n each each case predict predict what what would happen to the yield of hydrogen from a gi%en amount of methane. 8se 0e 4hatelierIs principle to explain your answer. (i) (i)
The The o%er o%eral alll pre press ssur uree is incr increa ease sed. d. Effect on yield of hydrogen hydrogen ......................................................... .............................................................................. ..................... Explanation .............................................................. ............................................................................................ ........................................ .......... ......................................................... ......................................................................................... .............................................................. .................................. .... ......................................................... ......................................................................................... .............................................................. .................................. ....
(ii) (ii)
The conc concent entrat ration ion of of steam steam in the the reacti reaction on mixtu mixture re is incr increas eased. ed. Effect on yield of hydrogen hydrogen ......................................................... .............................................................................. ..................... Explanation .............................................................. ............................................................................................ ........................................ .......... ......................................................... ......................................................................................... .............................................................. .................................. .... ......................................................... ......................................................................................... .............................................................. .................................. .... ()
(c)
At equilib equilibrium rium a high high yield yield of of hydrogen hydrogen is fa%oure fa%oured d by high temperatur temperature. e. 2n 2n a typical typical industrial process the operating temperature is usually less than 7;; <. /uggest two reasons why temperatures higher than this are not used. Reason 1 .......................................................... ........................................................................................ ........................................................... ............................. Reason 2 .......................................................... ........................................................................................ ........................................................... ............................. (2) (Total # marks)
15.
,ethanol can be synthesised s ynthesised from carbon monoxide by the re%ersible reaction shown below. 4!(g) " H(g)
4H:!H(g)
D ∆ H D
-7
-7 3F mol
The process operates at a pressure of @ ,>a and a temperature of =;; < in the presence of a copper9containing catalyst. This reaction can reach dynamic equilibrium. (a)
#y refer referenc encee to rates rates and and concen concentra tratio tions ns expl explain ain the the meani meaning ng of the term term dynamic eqili*rim$ .......................................................... ........................................................................................ .............................................................. ....................................... ....... .......................................................... ........................................................................................ .............................................................. ....................................... ....... (2)
(b)
Explai Explain n why a high high yield yield of metha methanol nol is fa%ou fa%oured red by by high high pressu pressure. re. .......................................................... ........................................................................................ .............................................................. ....................................... ....... .......................................................... ........................................................................................ .............................................................. ....................................... ....... (2)
(c )
/uggest two reasons why the operation of this process at a pressure much higher than @ ,>a would be %ery expensi%e. Reason 1............................. 1........................................................... ............................................................ ...................................................... ........................ Reason 2............................. 2........................................................... ............................................................ ...................................................... ........................ (2)
(d)
/tate the effec effectt of an increase increase in tempera temperature ture on the the equilib equilibrium rium yield of methano methanoll and explain your answer. Effect ....................................................... ..................................................................................... .............................................................. .................................. Explanation.......................... Explanation.......................................................... .............................................................. .................................................. .................... .......................................................... ........................................................................................ .............................................................. ....................................... ....... .......................................................... ........................................................................................ .............................................................. ....................................... ....... (!)
(e)
2f a cataly catalyst st were were not used used in this this proce process ss the the operat operating ing temp tempera eratur turee would would ha%e ha%e to be greater than =;; <. /uggest why an increased temperature would be required. .......................................................... ........................................................................................ .............................................................. ....................................... ....... (1) (Total 10 marks)
1.
The equation for the formation of ammonia is shown below. (g) " :H (g)
H:(g)
Experiment A was carried out starting with 7 mol of nitrogen and : mol of hydrogen at a constant temperature and a pressure of ; ,>a. 4ur%e A shows how the number of moles of ammonia present changed with time. 4ur%es , C and refer to similar experiments starting with 7 mol of nitrogen and : mol of hydrogen. 2n each experiment different conditions were used. ,
C A
, o le s o f a m m o n ia
.
T im e
(a )
!n cur%e A mar3 the point that represents the time at which equilibrium is first reached. 0abel this point X. (1)
(b) (b)
/tat /tatee 0e 4hat 4hatel elie ierI rIss pri princ ncip iple le.. .......................................................... ........................................................................................ .............................................................. ............................................. ............. .......................................................... ........................................................................................ .............................................................. ............................................. ............. (1)
(c)
8se 0e 0e 4hate 4hatelie lierIs rIs princi principle ple to ident identify ify whic which h one one of the the cur% cur%es es , C or represents an experiment carried out at the same temperature as experiment A but at a higher pressure. Explain why this cur%e is different from cur%e A. Crve ......................................................... ......................................................................................... .............................................................. .................................. .... Explanation .......................................................... ........................................................................................ ....................................................... ......................... .......................................................... ........................................................................................ .............................................................. ............................................. ............. .......................................................... ........................................................................................ .............................................................. ............................................. ............. .......................................................... ........................................................................................ .............................................................. ............................................. ............. (")
(d) (d)
2den 2denti tify fy whic which h one one of the the cur cur%e %ess , C or represents an experiment in which the conditions are the same as in experiment A except that a catalyst is added to the reaction mixture. Explain your choice of cur%e. Crve ......................................................... ......................................................................................... .............................................................. .................................. .... Explanation .......................................................... ........................................................................................ ....................................................... ......................... .......................................................... ........................................................................................ .............................................................. ............................................. ............. .......................................................... ........................................................................................ .............................................................. ............................................. ............. (!) (Total # marks)
1*.
$hen carbon monoxide reacts with steam at G=; < the following homogeneous dynamic equilibrium is established. 4!(g) " H !(g) (a )
(i)
4!(g) " H (g)
∆ H
-7
D 9 3F mol
Explain why this reaction is de descr scribed as a homogeneos reaction. homogeneos reaction. ......................................................... ......................................................................................... .............................................................. .................................. ....
(ii) (ii)
/tat /tatee wha whatt is is mea meant nt by the the ter term m dynamic eqili*rim. eqili*rim . ......................................................... ......................................................................................... .............................................................. .................................. .... ......................................................... ......................................................................................... .............................................................. .................................. .... ......................................................... ......................................................................................... .............................................................. .................................. .... (!)
(b)
/tate the effec effect t if any any of of the following following change changess on the the concentr concentration ation of hydroge hydrogen n in the the equilibrium mixture. 2n each case explain your answer. (i) (i)
An inc incre reas asee in the the conc concen entr trat atio ion n of of stea steam m Effect ............................................................ .......................................................................................... ..................................................... ....................... Explanation........................... Explanation......................................................... ............................................................ .............................................. ................ ......................................................... ......................................................................................... .............................................................. .................................. ....
(ii) (ii)
A decr decrea ease se in in the the tem tempera peratu ture re Effect ............................................................ .......................................................................................... ..................................................... ....................... Explanation........................... Explanation......................................................... ............................................................ .............................................. ................ ......................................................... ......................................................................................... .............................................................. .................................. .... ()
(c)
/tate and explain explain the the effect effect if any any of of a catalyst catalyst on the position position of this equilibrium equilibrium.. Effect ....................................................... ..................................................................................... .............................................................. ....................................... ....... Explanation.......................... Explanation.......................................................... .............................................................. ....................................................... ......................... (!) (Total 12 marks)
1$.
The industrial process for con%erting ammonia into nitric acid is carried out in three stages.
-7
Sta/% 1
H:(g) " @! (g)
!(g) " GH !(g)
∆H
D - -@; 3F mo mol
Sta/% 2
!(g) " ! (g)
!(g)
∆H
D -7 -77 3F mo mol
Sta/% !
:!(g) " H!(l)
H!:(aq) " !(g)
∆H
D -7 -77= 3F mo mol
(a) (a)
-7
-7
4onsi onside derr th the rea react ctio ion n in in Sta/% 1 abo%e. (i)
/tate /tate how how the temper temperatu ature re shou should ld be change changed d in order order to increa increase se the the yield yield at at equilibrium in this reaction. Explain your answer. Temperatre change......................... change....................................................... ............................................................ .................................. .... Explanation........................... Explanation......................................................... ............................................................ .............................................. ................ ......................................................... ......................................................................................... .............................................................. .................................. ....
(ii) (ii)
/tate /tate how how the pres pressure sure should should be be change changed d in order order to to increa increase se the the yield yield at equilibrium in this reaction. Explain your answer. Pressre change change........................... ......................................................... ............................................................ ....................................... ......... Explanation........................... Explanation......................................................... ............................................................ .............................................. ................ ......................................................... ......................................................................................... .............................................................. .................................. .... (")
(b)
The Sta/% 1 reaction is carried out by passing ammonia and air o%er a platinum gauze at a temperature of ;;J4 and a pressure of =;;3>a. (i)
$hat $hat are are the the ad%an ad%antag tages es of of using using this this temper temperatu ature re and and this this pressur pressure1 e1 Temperatre........................... Temperatre......................................................... ............................................................ ............................................. ............... Explanation........................... Explanation......................................................... ............................................................ .............................................. ................
(ii) (ii)
i%e i%e two reason reasonss why the cata catalys lystt is used used in the form form of a gauz gauze. e. Reason 1............................ 1.......................................................... ............................................................ .................................................. .................... Reason 2............................ 2.......................................................... ............................................................ .................................................. .................... (")
(c)
The reac reactio tion n by which which ! is is formed formed direc directly tly from from nitr nitroge ogen n and oxyg oxygen en is shown shown below below.. (g) " !(g) (i) (i)
!(g)
∆ H
-7
D "7; 3F mol
i%e i%e the the nam namee for for the the enth enthal alpy py cha chang ngee for for this this rea react ctio ion. n. ......................................................... ......................................................................................... .............................................................. .................................. .... ......................................................... ......................................................................................... .............................................................. .................................. ....
(ii) (ii)
Expl Explai ain n ful fully ly the the mean meanin ing g of of the the symb symbol ol ......................................................... ......................................................................................... .............................................................. .................................. .... ......................................................... ......................................................................................... .............................................................. .................................. .... ......................................................... ......................................................................................... .............................................................. .................................. ....
(iii)
/uggest /uggest why reactio reactions ns between between nitroge nitrogen n and oxyge oxygen n are often often consider considered ed to be be en%ironmentally unfriendly unfriendl y. ......................................................... ......................................................................................... .............................................................. .................................. .... ......................................................... ......................................................................................... .............................................................. .................................. ....
(i%)
Explain Explain why the decomp decomposition osition of ! into its its elements elements is fa%oured fa%oured by a low temperature. ......................................................... ......................................................................................... .............................................................. .................................. .... ......................................................... ......................................................................................... .............................................................. .................................. .... (*)
(d) (d)
#y cons consid ider erin ing g the the reac reacti tion onss in in Sta/% 2 and Sta/% ! suggest how the o%erall yield of nitric acid could be increased without altering either the temperature or the pressure chosen for each of the three stages. .......................................................... ........................................................................................ .............................................................. ............................................. ............. .......................................................... ........................................................................................ .............................................................. ............................................. ............. (2) (Total 1* marks)
1#.
(a)
Hydrog Hydrogen en used used in the Habe Haberr >roces >rocesss is produce produced d in the foll followi owing ng dynam dynamic ic equil equilibr ibrium ium reaction. 4H(g) " H!(g)
(i)
4!(g) " :H(g)
2n terms terms of rates rates and of concen concentra tratio tions ns what what does does the term dynamic eqili*rim mean1 Rates ........................................................... ......................................................................................... .................................................. .................... Concentrations ........................................................... ......................................................................................... ................................... .....
(ii) (ii)
/tate /tate how an incre increase ase in pressu pressure re will will affect affect the equil equilibr ibrium ium yield yield of hydro hydrogen gen.. Explain your answer. Eqili*rim yield ................................ yield .............................................................. .......................................................... ............................ Explanation ............................................................ ............................................................................................ ...................................... ...... ......................................................... ......................................................................................... ............................................................. .............................
(iii)
The equilibr equilibrium ium yield yield of hydrogen hydrogen is reduce reduced d when the reaction reaction is carried carried out out at a lower temperature. $hat can be deduced about the enthalpy change in this reaction1 ......................................................... ......................................................................................... ............................................................. .............................
(i%)
Explain Explain why the equilib equilibrium rium yield is unchang unchanged ed when when a cataly catalyst st is introd introduced. uced. ......................................................... ......................................................................................... ............................................................. ............................. ......................................................... ......................................................................................... ............................................................. ............................. ($)
(b)
Ammoni Ammoniaa is produc produced ed in the the Haber Haber >roces >rocesss accordi according ng to the the follow following ing equat equation ion.. (g) " :H (g)
H :(g)
∆ H f
Typical Typical operating conditions are @; J4 and ; ,>a (;; bar).
-7
D - 3F mol
(i) (i)
Expl Explai ain n why why @; @; J4 is a com compr prom omis isee tem temper perat atur ure. e. ......................................................... ......................................................................................... ............................................................. ............................. ......................................................... ......................................................................................... ............................................................. ............................. ......................................................... ......................................................................................... ............................................................. ............................. ......................................................... ......................................................................................... ............................................................. .............................
(ii) (ii)
Expl Explai ain n why why ; ; ,>a ,>a is a comp comprom romise ise press pressur ure. e. ......................................................... ......................................................................................... ............................................................. ............................. ......................................................... ......................................................................................... ............................................................. ............................. ......................................................... ......................................................................................... ............................................................. ............................. ......................................................... ......................................................................................... ............................................................. ............................. () (Total 1" marks)
20.
,ethanol 4H:!H is a con%enient liquid fuel. (a)
An exper experime iment nt was cond conduct ucted ed to determ determine ine the the enthal enthalpy py of comb combust ustion ion of of liquid liquid methanol. The energy obtained from burning .7 g of methanol was used to heat 7@; g of water. The temperature of the water rose from < to :G <. (The specific heat -7 -7
capacity of water is .7 F < g ) (i)
'efine the term standard enthalpy of of com*stion. com*stion .
(ii)
8se the the data data abo%e abo%e to calcula calculate te a %alue for the enthalpy enthalpy of of combust combustion ion of of one one mole mole of liquid methanol. (*)
(b)
,ethanol ,ethanol can can be be synthesis synthesised ed from from methane methane and steam by a process process that that occurs occurs in two two stages. "tage 1 4H(g) " H !(g) "tage 2 4!(g) " H (g)
∆ H
:H(g) " 4!(g) is 4H:!H(g)
∆ H
&
&
" ; G 3 F m o l
- A 7 3 F m o l
- 7
- 7
(i)
Explain why in "tage 1 1 a higher yield of hydrogen and carbon monoxide is ot obtained if the pressure is increased.
(ii)
"tage 2 is carried out at a compromise temperature of @;;<. #y considering what would happen at higher and lower temperatures explain why @;; < is considered to be a compromise for "tage 2. 2. (5)
(c)
The stan standar dard d enthal enthalpie piess of combust combustion ion of of carbon carbon monox monoxide ide and and of hydro hydrogen gen are are -7
-7
-: 3F mol and -G 3F mol respecti%ely. 8se these data and the enthalp y change for "tage 2 to calculate a %alue for the standard enthalpy of combustion of gaseous methanol. (!)
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21.
$hen ammonia gas is heated a homogeneous dynamic equilibrium is established between ammonia and its constituent elements. This decomposition decomposition is endothermic. (a )
Explain th the te terms homogeneos+ dynamic and eqili*rim and eqili*rim.. $rite an equation for this decomposition and deri%e an expression for the equilibrium constant ' constant ' c (5)
(b)
/tate /tate and expla explain in the condi condition tionss under under which which a high equil equilibr ibrium ium conce concentr ntratio ation n of hydrogen would be obtained. (")
(c)
The deco decomp mposit osition ion of of ammoni ammoniaa might might in the the future future be used used as an indu industr strial ial meth method od for the manufacture of hydrogen. Explain why an industrial chemist might decide to use conditions different from those you ha%e gi%en in part (b) if large quantities of hydrogen were to be produced by this decomposition. 'iscuss the effect that using a catalyst would ha%e on the equilibrium yield and on the amount of hydrogen which could be produced in a gi%en time. () (Total 15 marks)
22.
Hydrogen is produced by the reaction between steam and methane when the following dynamic equilibrium is established. 4H(g) " H!(g)
(a)
4!(g) " :H(g)
D ∆ H D
-7
";G 3F mol
8se 0e 0e 4hatelie 4hatelierIs rIs principle principle to predict predict the separate separate effects effects of an an increase increase in temperatu temperature re and of an increase in pressure on the yield of hydrogen obtained in the abo%e reaction. 2n each case explain your answer. ()
(b)
/tate /tate how how and and explain explain why why the use use of a cataly catalyst st might might or migh mightt not chang changee the equilibrium yield of hydrogen and also the amount of hydrogen produced in a gi%en time. (") (Total 10 marks)
2!.
(a )
'efine th the te term activation energy for a reaction. .......................................................... ........................................................................................ .............................................................. ....................................... ....... .......................................................... ........................................................................................ .............................................................. ....................................... ....... (2)
(b) (b)
i%e i%e the the mea meani ning ng of the the ter term m catalyst$ .......................................................... ........................................................................................ .............................................................. ....................................... ....... .......................................................... ........................................................................................ .............................................................. ....................................... ....... (2)
(c) (c)
Expl Explai ain n in gene genera rall term termss how how a cat cataly alyst st wor wor3s 3s.. .......................................................... ........................................................................................ .............................................................. ....................................... ....... .......................................................... ........................................................................................ .............................................................. ....................................... ....... (2)
(d) (d)
2n an expe experi rim ment ent two two mol moles es of gas gas reacted completely with solid + to form one mole of gas as shown in the equation below. $(g) " +(s)
→
K(g)
The graph below shows how the concentration of %aried with time at constant temperature.
n o i t a r t n e c n o 4
T im e
(i)
!n the the axes axes abo%e abo%e s3etc s3etch h a cur%e cur%e to show show how the concen concentra tratio tion n of of would change with time in the same experiment. 0abel this cur%e .
(ii) (ii)
!n the the axes axes abo%e abo%e s3etc s3etch h a cur%e cur%e to show show how how the concen concentra tratio tion n of would change with time if the reaction were to be repeated under the same conditions but in the presence of a catalyst. 0abel this cur%e .
(iii)
2n terms terms of the beha%iour beha%iour of of particles particles explain explain why the the rate rate of this this reaction reaction decreases with time. ......................................................... ......................................................................................... ............................................................ ............................ ......................................................... ......................................................................................... ............................................................ ............................ () (Total 12 marks)
