CHEMICAL EQUILIBRIUM I.
INTRODUCTION A. Princi incipl ple e If you are in a bus stop and you observed that the rate at which people ride the bus is equal to the rate at which people leave the bus, the number of people riding the bus and leaving the bus remains constant and can be said to be in dynamic equilibrium, much much like in chemicals chemicals reactions. reactions. They can occur in both forward forward and reverse directions, and when the rates of reactions became equal, the concentrations of reactants and products remain constant; at that point, the chemical system is at equilibrium !c!urry" #ay, $%%&'. (hemical (hemical equilibriu equilibrium m as de)ned by *ower *ower is a chemical chemical reaction reaction in which which there is no tendency for the quantities of reactants and products to change. (hemical change occurs when the atoms that make up one or more substance rearrange in such a way that new substances are formed. These substances are the components of the chemical reaction system; those components which decrease in quantity are called reactants while those which increase increase are called products. A given chemical reaction system is de)ned by a balanced net chemical reaction which is conventionally written as + eactants - products There are are some factors factors which instigate instigate these changes to disturb disturb a system system at equilibrium namely, the concentration, pressure and temperature. The e/ect of any any change in the reaction reaction condition of a system in equilibrium equilibrium can be described using the *e (hatelier0s Princ Principle. iple. The principle states that if a system at equilibrium is sub1ected to a change of pressure, temperature, or number of moles of a substance, there there will be a tendency for a net reaction in the direction that tends to reduce the e/ect of this change.
2. 3b1ectives At the end of the e4perimentation, the student was able to+ 5. to determine how di/erent factors a/ect a system in chemical equilibrium; $. to e4plain the e/ect of these factors in terms of the *e (hatelier0s principle. II.
MATERIALS A. eagents %.%$ ! 67(8 9$3 %.%$ ! #e83:': 8a8%$ %.%$ ! 8a9$P3 < ! 9(* (o(l$ ice 2. Apparatus Test tube 7tirring rod (entrifuge tubes 7yringe ubber stopper 9ot plate 2eaker
III.
PROCEDURE A. =/ect of (oncentration > ml of %.%$ ! 67(8 was mi4ed with > ml water in a test tube. Afterwards, $- drops of %.%$ ! #e83 :': was added to the solution in the test tube and was stirred. 3bservations were noted and were recorded on the table provided. 7ubsequently, the formed solution was divided into four labelled test tubes 5-'. The )rst test tube served as the control in the e4periment. The second was added with a small crystal of 67(8. Test tube : was added with a drop of %.%$ #e83 :': and test tube with $ drops of %.%$ ! 8a9 $P3. 3bservations on physical properties of the solution on each testtube were recorded on the table.
2. =/ect of Pressure ?nder the fumehood, a pinch of 8a83$ and :- drops of ml of this solution. 3ne test tube was placed in a hot-water bath, the second in a cold-water bath, and the third, in room temperature which served as the control. After > mins, observations on the color variations of each solution were noted. Afterwards, the test tube from the hot-water bath was transferred to the cold-water bath and vice versa. It was allowed to stand for another > minutes then the observations were again noted on a table.
IV.
DATA AND RESULTS
Table .5 3bservations on the addition of %.%$ ! #e83 :':to 67(8 solution. Step
Observations
Preparation of > ml %.%$ ! 67(8 @ > ml 9$3
(lear, colorless solution
Addition of $- drops of %.%$ ! #e83 :':
eep red solution
Table .$ Preparation of di/erent solutions of 67(8.
T=7T
(38T=8T7
327=BATI387
5
Prepared solution
2loody red in solution
$
Prepared solution @ 67(8
ark red solution
T?2=
crystal
:
Prepared solution@ 5 drop %.%$
arker red solution in reference to test
! #e83:':
tube no.$'
Prepared solution @ $ drops %.%$ %.%$ ! 8a9 $P3
Cellowish solution
Table .: =/ect of pressure on color changes of gas.
Srin!e p"#n!er position
Observations
2
2rown gas
(.
*ight brown gas
A. *ighter brown gas Table . =/ect of temperature to the (o(l$ solution.
Initia" Te$perat# re
Observations
S%i&tin! Te$perat#r e
Observations
9ot-temp
Biolet solution
(ol temp
*ighter pink solution refer to test tube in room temp.'
(old temp
*ighter pink solution refer to test tube in room temp.'
9ot temp
Biolet solution
oom temp
Pink solution
oom temp
Pink solution
V.
DISCUSSION (hemical equilibrium is the state reached when the concentrations of reactants and products remain constant over time. There are some factors which instigate these changes to disturb a system at equilibrium namely, the concentration, pressure and temperature. Table .5 shows the observations as 67(8 was added with drops of #e83:':. It can be observed that when 67(8 was )rst added with water, the solution formed was colorless and when the additional drops of #e83:': was dispersed in the test tube, the colorless solution turned to a bloody red solution which is due to the formation of #e7(8$@ with a net ionic equation of+ #e:@ @ 7(8 - #e7(8$@
Table .$ shows the variation in the color of the solution as di/erent reagents were added on it. 7hifts in the position of its equilibrium can be detected by observing how the color of the solution changes when various reagents were added. #or e4ample, as an additional crystal of 67(8 was added to the test tube containing #e7(8$@ solution, the color of the solution turned to a darker shade of red, in contrast to the bloody red color of the test tube containing #e7(8$@ alone.
#urthermore, as #e83:': was added to another test tube containing the prepared solution of #e7(8$@, the color also changes, presenting a a darker shade of red. 9owever, when 8a9$P3 was added to the solution, the color of the solution changes to a yellowish one which can be e4plained by using *e (hatelier0s Principle. *e (hatelier0s Principle states that the concentration stress of an added reactant or product is relieved by net reaction in the direction that consumes the added substance furthermore, the concentration stress of a removed reactant or product is relieved by net reaction in the direction that replenishes the removed substance. As #e7(8$@ reacts with 67(8, the concentration of stress added of 7(8-shifts the equilibrium from left to right and the red color gets darker. 7imilarly, as #e83:': was dropped in the solution, the concentration stress of added #=:@ is relieved by net reaction from left to right which consumes the #e:@ and increase the concentration of #e7(8$@ making the solution change to a darker shade of red !c!urry" #ay, $%%&'. 9owever, !c!urry and #ay $%%&' added that as *e (hatelier0s Principle is a handy rule for predicting chanhes in the composition of an equilibrium mi4ture, it doesn0t e4plain why those changes occur. 7o in order to thoroughly picture out how the principle works, we can use the mathematical relationshipaA @ b2 -c( @ d speci)cally the *aw of !ass Action which is represented by the following e4pression+ 6eq D E(Fc EFd G EAFa E2Fb Hherein the quotient c' is equal to 6eq presenting a system at equilibrium. Hhen the equilibrium is disturbed by increasing the concentration of reactant, the denominator of the equilibrium constant e4pression increases yielding a quotient c' less than the 6eq, so for the system to move to a new state of equilibrium, the c must increase by increasing the numerator product' and decreasing the denominator. In line with the e4periment, as the #e7(8$@ was added with 7(8, the concentration of the reactant increases, making the quotient less than the
supposedly 6eq. 7o the tendency of the system is to increase the quotient by raising the amount product and reducing the reactants so the reaction will have a forward shift, thereby increasing the quotient to ad1ust the system to equilibrium. The constants 6c 6eq' and 6p for the general gas-phase reaction aA @ b2 -c( @ d are related because the pressure of each component in a mi4ture of ideal gases is directly proportional to its molecular concentration. The equilibrium equation for 6p is therefore given by+ c d 6pD P(' P D E(F c EF d J T c@d' - Ka@b' ' PA'aP2'b EAF a E2F b Therefore, 6pD 6c T' An' 2ecause gas pressures are easily measured, equilibrium equations for gasphase reactions are often written using partial pressures. The partial pressure of a gas in a mi4ture is the pressure the gas would e4ert if it were the only one present and is independent of the partial pressures of the other gases in the mi4ture. In relation to this, Table .: shows the variations of color as the pressure in the syringe was increased showing the e/ect of pressure on chemical equilibrium. It was observed that as the plunger was pushed until the cc mark, the brown gas turned to a lighter shade of brown. As *e (hatelier0s Principle state, An increase in pressure by reducing the volume will bring about net reaction in the direction that decreases the number of moles of gas while a decrease in pressure will bring about net reaction in the direction that increases the number of moles of gas. $ no$ - 8$3 Increasing the pressure on this equilibrium system will result in the equilibrium position shifting to reduce the pressure, that is, to the side that has the least number of gas particles.There are $ gas particles on the left hand side of the reaction and 5 gas particle on the right hand side of the reaction.Increasing the pressure on this system results in the equilibrium position moving to the right, consuming 83$g' and producing more 8 $3g'. The system will become a lighter red-brown colour. Thus, increase in pressure favors the backward reaction and vice versa. !eanwhile, Table . shows the e/ect of temperature on the chemical equilibrium. As the
prepared solution was put on the cold water bath, the intial pink
solution turned to a lighter shade of pink and the test tube that was placed on the hot water bath turned to violet solution. Afterwards, as the temperature was shifted from hot to cold temperature, and cold to hot temperature, the color of the solution also shifted from light pink to violet and vice versa. #or an endothermic reaction such as the reaction of the prepared solution of (o(l$, heat is absorbed by the reaction in the forward direction. The equilibrium therefore shifts to the product side at the higher temperature which means that equilibrium increases with increasing temperature making the pink solution turned to a violet one. And the e4othermic reaction of (o(l$ wherein heat is released made possible the color alteration of the pink solution to a lighter shade. The equilibrium constant for an e4othermic reaction decreases as the temperature increases wherein the energy can be considered as a product of the reaction. !eanwhile, in an endothermic reaction, the equilibrium constant is directly proportional to the temperature which means that as 6c increases, the temperature also increases and the energy can be considered as a reactant of the reaction. Cou can predict the way in which 6c depends on temperature by using *e (hatelier0s Principle. As it says, if heat is added to an equilibrium mi4ture thus increasing its temperature, net recation occurs in the direction that relieves the stress of the added heat. To generaliLe the idea, in an =ndothermic =quilibrium 7ystems, Increasing the temperature of the equilibrium system will shift the equilibrium position to the side that does not include the energy term in order to reduce the temperature, that is to the rightmakinf the color of the solution darker.Hhereas in an =4othermic =quilibrium 7ystems,Increasing the temperature of this equilibrium system shifts the equilibrium position to the left, consuming some of the energy and products to produce more reactants making the color of the solution lighter.
VI.
CONCLUSION
(hemical equilibrium is the state reached when the concentrations of reactants and products remain constant over time. There are some factors which instigate these changes to disturb a system at equilibrium namely, the concentration, pressure and temperature. The e/ect of any change in the reaction condition of a system in equilibrium can be described using the *e (hatelier0s Principle. 3n the e/ect of concentration on chemical equilibrium, *e (hatelier0s Principle states that the concentration stress of an added reactant or product is relieved by net reaction in the direction that consumes the added substance furthermore, the concentration stress of a removed reactant or product is relieved by net reaction in the direction that replenishes the removed substance which is supported by the variations on the color of the #e7(8$@ solution as they were added with di/erent substances. !eanwhile, *e(hatelier0s Principle states that An increase in pressure by reducing the volume will bring about net reaction in the direction that decreases the number of moles of gas while a decrease in pressure will bring about net reaction in the direction that increases the number of moles of gas which e4plains why the color of the gas changes from brown to a lighter shade . #urthermore, he described the e/ect of temperature on the equilibrium constant, in two ways for an =ndothermic reaction, Increasing the temperature of the equilibrium system will shift the equilibrium position to the side that does not include the energy term in order to reduce the temperature, that is to the right making the color of the solution darker which e4plains why the test tube that was put on the hot water bath became violet.
Hhereas in an
=4othermic reaction, Increasing the
temperature of this equilibrium system shifts the equilibrium position to the left, consuming some of the energy and products to produce more reactants making the
color of the solution lighter and which e4plains why the solution placed on the cold water bath turns light pink.
VII.
LITERATURE CITED *ower, 7.6. $%%5.Chemical Equilibrium: A chemical 1 reference text. (alifornia+ 8P. !c!urry, M.= " #ay, .(. $%%&. Chemistry . >thed.'.Pof pub+ Prentice 9all. Atkin, P. " de Paula, M. $%5%. Physical Cehmistry for the Life Sciences. $nded.'. Place of pub+ 34ford ?niversity Press. http+GGwww.ausetute.com.auGlechatsp.html
