Experiment 8: Chemical Kinetics Ca!eliña, "oren Ga#rielle $ %&tana, Ma'neth (ince
TCD2, Group 8, Mr. Julius Nuñe March )*, 2+)2
I. Abstract Chemistr', #' its er' nature, is concerne! -ith chane. Much o& the stu!' o& chemical reactions is concerne! -ith the &ormation o& ne- su#stances &rom ien reactants #ut, it is e/uall' important to un!erstan! ho- rapi! these reactions occur. Chemical Kinetics is the area o& chemistr' concerne! -ith the spee! at -hich a chemical reaction occurs. 0ccor!in to the collision theor' o& chemical 1inetics, a chemical reaction is the result o& the e&&ectie collision #et-een the molecules. 0 collision is e&&ectie i& the molecules are suita#l' oriente! to &orm ne- #on!s an! possess the actiation ener' re/uire! to in!uce the reaction. ecause reactions inole #rea1in an! &ormin o& #on!s, the spee! o& the reaction !epen!s on the nature o& the reactants themseles. The &actors -hich a&&ect the rates at -hich particular reactions occur are the ph'sical state o& the reactants, the concentration o& the reactants, the temperature at -hich the reaction occurs an! the presence o& a catal'st. 3n the experiment, the relatie rates o& reaction #et-een the solutions in -hich one is altere! un!er the con!itions -hich a&&ect the rate is compare!. 4rom this experiment, it coul! #e !e!uce! that reactions procee! &aster -hen the sur&ace area, the concentration an! the temperature o& the reactants is increase! an! -hen there is a catal'st catal'st present. Chemical 1inetics 1inetics is a er' #roa! su#5ect su#5ect encompassi encompassin n eer'!a' eer'!a' li&e routines 6en'me catal'sis, ho- &ast -oul! me!icines ta1e e&&ect, etc.7 an! in!ustrial challenes such as the !eelopment o& catal'sts -hich are er' use&ul in s'nthesiin ne- materials. These processes pla' a er' sini&icant role in our lies. II. Keywords: chemical 1inetics, reaction rate, collision theor', catal'st, actiation ener', &actors a&&ectin rates
Chem ).) Chemical Kinetics
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III. Introduction Chemical Kinetics is concerne! -ith the rates or the spee! o& reactions. %n the molecular leel, reaction rates !epen! on the &re/uenc' o& collisions #et-een molecules. The reater the &re/uenc' o& collisions, the reater is the rate o& reaction.4or a collision to lea! to a reaction, ho-eer, it must occur -ith su&&icient ener' to stretch the #on!s to a critical lenth an! -ith suita#le orientation &or ne- #on!s to &orm in the proper locations. There&ore, this experiment -as carrie! out to ena#le the stu!ents to reconie the &actors a&&ectin the reaction rates, to !etermine the e&&ects o& the nature, concentration, temperature an! sur&ace area o& the reactants an! catal'st on the rate o& the reaction an! to explain the e&&ects o& these &actors. IV. Experimental 4or the part inolin the e&&ect o& the nature o& reactants, 2+ !rops o& +.) M KMn% an! )2 !rops o& M ; 2<% -as mixe! in a =>ml test tu#e an! ten !rops o& the mixture -as trans&erre! to each o& the 2 test tu#es. )+ !rops o& +.) M Na2C2% solution -as a!!e! to the &irst test tu#e -hile )+ !rops o& ; 2%2 solution -as a!!e! to the secon! one. The rate o& !iscoloration o& KMn% in the 2 test tu#es -as note! an! compare!. )+ !rops each o& M, * M an! ) M ;Cl -as put into * separate test tu#es. * small pieces o& the M ri##on -hich -ere o& the same sie -as secure! an! ) piece -as a!!e! to each o& the test tu#es. The time it too1 &or the M ri##on to completel' !issole in the aci! -as recor!e!. This part is rear!in the e&&ect o& concentration. )+ !rops o& +.)= M Na 2<2%* -as place! in a =>ml test tu#e an! the solution -as heate! in a -ater #ath until the temperature o& the #ath is + ?C. )+ !rops o& * M ;Cl -as then a!!e!. The time &rom the instant the aci! -as a!!e! until the solution turne! clou!' -as recor!e!. This proce!ure -as repeate!, this time, &or another Na2<2%* solution heate! to + ?C an! the other Na2<2%* solution -hich -as coole! to 2+ ?C in ice or col! -ater. The e&&ect o& temperature -as teste! here. @ear!in the e&&ect o& sur&ace area, a small piece o& chal1 -as place! in a test tu#e. 0 cr'stal -ith the same sie -as rin!e! an! place! in another test tu#e. 2+ !rops o& ) M ;Cl -as a!!e! to each an! the relatie rates o& reaction -ere compare!. 4or the part inolin the e&&ect o& a catal'st, )+ !rops o& &reshl' prepare! ;2%2 -as place! in a test tu#e an! a pinch o& Mn%2 -as a!!e! to it. The eolution o& %2 as -as teste! throuh the use o& a lo-in splinter hel! near the mouth o& the test tu#e. The proce!ure -as repeate! Chem ).) Chemical Kinetics
-ithout a!!in Mn%2. The relatie rates o& the eolution o& as in the 2 test tu#es are compare!. V. Results @E"0T3(E @0TE %4 @EDAC3NG 0GENT
D3<099E0@0NCE %4 93NK C%"%@ 3N T;E <%"AT3%N slo-er &aster
Na2C2% ;2%2
Ta#le ): E&&ect o& the Nature o& @eactant
C%NCENT@0T3%N %4;Cl M *M )M
T3ME 6secon!s7 *+ =+ B+
Ta#le 2: E&&ect o& the Concentration
TEM9E@0TA@E 6?C7 2+ + +
T3ME 6secon!s7 8.)+ 2.*+ )
Ta#le *: E&&ect o& the Temperature
@E"0T3(E @0TE %4 E(%"AT3%N %4 A"E< &aster slo-er
Ta#le : E&&ect o&
"3A3D <%"AT3%N ithout Mn% 2 ith Mn%2
@E"0T3(E @0TE %4 E(%"AT3%N %4 %2 G0< slo-er &aster
Ta#le =: E&&ect o& Catal'st
VI. Discussion The solution containin KMn% an! ;2<% -as oriinall' pin1ish in color. ith the ; 2%2 as the re!ucin aent, it cause! the !iscoloration o& the solution &aster than Na2C2%. This is !ue to the unsta#ilit' o& ;2%2 contri#utin to a lo- actiation ener'. 0s a eneral rule, the lo-er the actiation ener', the &aster -ill a reaction procee!. Mn F -as re!uce! to colorless Mn2F turnin the solution to colorless. The e&&ect o& concentration is sho-n in ta#le 2. The &astest spee! o& reaction is o#sere! in the test tu#e containin M ;Cl, &ollo-e! #' the * M ;Cl an! then the ) M ;Cl. This sho-s that increasin concentration spee!s up the rate o& the 9ae 2 o&
reaction #ecause the &re/uenc' at -hich the reactant molecules colli!e also increases. This is !ue to the &act that -ith increase! concentration, there is more moles o& the reactant per unit o& the olume, an! the chances the molecules -oul! colli!e are more &re/uent &aorin the collision theor'. Temperature is also one o& the &actors a&&ectin the reaction rates. 3t is proportional to the 1inetic ener' o& the reactant molecules there&ore, i& the temperature in Kelin is !ou#le!, the aerae 1inetic ener' o& the molecules is also !ou#le!. 4ollo-in this relationship, the molecules -oul! colli!e more &re/uentl' -ith een reater intensit', lea!in to increase! rates o& the reaction as can #e seen &rom the !ata in ta#le * in -hich the reaction procee!s the &astest un!er the temperature o& + ?C in comparison to the solution heate! up to + ?C onl' #e&ore the * M ;Cl -as a!!e! an! the solution -hich -as coole! up to 2+ ?C in -hich the reaction rate is the slo-est. @eactants must come toether in or!er &or them to react, an! the reaction is limite! to the area o& contact, thus, reactions that inole soli!s ten! to procee! &aster i& the sur&ace area o& the soli! is increase!. 0s seen in ta#le , the relatie rate o& the eolution o& #u##les in the solution containin the soli! -hich is po-!ere! is &aster in comparison to the other solution in -hich a -hole lump o& soli! is a!!e!. 3ncreasin the sur&ace area also increases the &re/uenc' o& collisions -hich is also another reason -h' this &actor also increases the rate at -hich the reaction procee!s. 0 catal'st is an aent that increases reaction rates throuh lo-erin the oer>all actiation ener' o& the sai! reaction. This is !one throuh the proision o& a !i&&erent mechanism &or the reaction. 3n this experiment, a!!in Mn%2 to ;2%2 hastene! its !ecomposition to ox'en as an! -ater. Mn%2 sere! as a heteroeneous catal'st, a catal'st that is in a !i&&erent phase -ith the reactants. 3t -as &irst re!uce! in the reaction an! then oxi!ie! to reenerate itsel& at the en! o& the reaction. VII. Guide Questions & Answers ). hich is the stroner re!ucin aent, Na2C2% or ;2%2H h'H The stroner re!ucin aent is ;2%2. 3t cause! the !isappearance o& the pin1ish color o& the solution &aster compare! to Na2C2% #' re!ucin MnF to Mn F2. The reaction also procee!e! &aster !ue to the lo- actiation ener' o& ; 2%2. 2. hat conclusions can 'ou ma1e rear!in the e&&ect o& nature o& reactants on the rate o& reactionH 3n!ii!ual properties o& the reactants also a&&ect the reaction rates. 3n eneral, the reaction Chem ).) Chemical Kinetics
rate is slo-er -hen the reactants are lare an! complex molecules. ith relation to the #on! t'pe, reactions inolin ionic species procee! &aster than those inolin molecular #on!s. @eactions inolin -ea1 #on!s procee! &aster compare! to those -hich inole #rea1in o& stron #on!s. *. ase! on 'our o#serations, -hat is the relationship #et-een: a. Concentration o& reactant an! time o& reactionH Most chemical reactions procee! &aster i& the concentration o& one or more o& the reactants is increase! #ecause as the concentration increases, the &re/uenc' -ith -hich the reactant molecules colli!e increases, lea!in to increase! rates. There&ore, the hiher the concentration o& the reactant, the shorter is the time o& the reaction. #. Time o& reaction an! spee! o& reactionH The &aster the spee! o& the reaction, the shorter is the time o& the reaction an! ice>ersa. c. Concentration o& reactant an! spee! o& reactionH 0s the concentration o& the reactant is increase!, the &re/uenc' o& the collision #et-een the reactant molecules is also increase! lea!in to increase! rates o& the reaction. There&ore increasin the concentration o& the reactant hastens the spee! o& the reaction. . ;o- !oes chane in temperature a&&ect the rate o& a reactionH 3ncreasin the temperature also increases the 1inetic ener' o& the molecules. 0s the molecules moe more rapi!l', the' colli!e more &re/uentl' an! also, -ith hiher ener' lea!in to increase! reaction rates. =. ;o- !oes particle sie or sur&ace area a&&ect the rate o& reactionH @eactions procee! &aster i& the sur&ace area o& the reactant is increase! #ecause there is a reater area o& contact aaila#le &or the molecules to colli!e. . hat is the role o& Mn%2 in the experimentH Mn%2 sere! as a catal'st in the experiment. 3t ma!e the !ecomposition o& ; 2%2 into -ater an! ox'en as spee! up. . ;o- !oes a catal'st a&&ect the rate o& a chemical reactionH 0 catal'st ma' a&&ect the rate o& the reaction #' alterin the alue o& either the actiation ener' 6Ea7 or the &re/uenc' &actor 607. 3t usuall' lo-ers 9ae * o&
the oerall actiation ener' &or a chemical reaction #' proi!in a !i&&erent mechanism &or the reaction. 8. The &ollo-in !ata -ere o#taine! &rom a h'pothetical reaction -herein reactants 0, , an! C &orm pro!uct D. A! "mol#$% +.+*+ +.++ +.++ +.+*+
! "mol#$% +.+*+ +.+*+ +.+= +.+*+
'! "mol#$% +.+)+ +.+2+ +.+2+ +.++
Rate "mol#$%#sec +.*+x)+> ).2+x)+> ).8+x)+> +.*+x)+>
a. hat is the or!er o& reaction -ith respect to 0H -ith respect to H -ith respect to CH ith respect to 0: x ' @ate2I).2 x )+>I I 16+.++7 6+.+*+7 I 627x > x ' @ate) +.* x )+ 16+.+*+7 6+.+*+7 627xI
xI2 secon! or!er
ith respect to : x ' @ate*I).8 x )+>I *I16+.++7 6+.+=7 6+.+2+7 I 6*7' > x ' @ate2 ).2 x )+ 2 16+.++7 6+.+*+7 6+.+2+7 627' 6*27'I6*27 'I) &irst or!er ith respect to C: x ' @ate I+.* x )+>I)I 16+.+*+7 6+.+*+7 6+.++7 I 67 > x ' @ate) +.* x )+ 16+.+*+7 6+.+*+7 6+.+)+7 67I)
I+ ero or!er
#. hat is the rate e/uationH Gie the oer>all or!er o& reaction !escri#e!. @ateI10L2L)CL+ or @ateI10L2L The oer>all or!er o& reaction: 62F)F+7I* thir! or!er c. hat is the numerical alue o& the rate constant, 1H 1I rate I +.*+ x )+> I )+ or ).)) M>2s>) 0L2L 6+.+*726+.+*7 B
VIII. 'onclusions & Recommendations 3t ma' #e loical to assume that chemical reactions occur as the result o& collision #et-een reactant molecules in terms o& the collision theor' o& chemical 1inetics, #ut collisions alone !o not uarantee that a reaction -ill ta1e place. This is !ue to the &act that there is a minimum collision ener' #elo- -hich, no reaction occurs. 3n or!er &or the colli!in molecules to react, the' must possess certain actiation ener', the minimum ener' re/uire! to initiate a chemical reaction. 0lso, the molecules must #e oriente! in some -a' that the' are suita#l' positione! to &orm ne- #on!s. The process in -hich a reaction occurs is calle! the reaction mechanism. The rate at -hich this reaction occurs is the primar' concern o& chemical 1inetics. The rate o& reactions are a&&ecte! #' the nature, the concentration an! the sur&ace area o& the reactants, the temperature at -hich the reaction occurs an! the presence o& a catal'st. 0lso, 1inetics in chemistr' re&ers to the chane in concentration o& the reactant -ith time. 3t -oul! #e i!eal to #e a#le to !etermine ho- the initial rate !epen!s on the startin concentrations an! the rate la- ta1es the &orm o& rateI10L xL'. This e/uation also ies us the reaction or!er -hich ena#les us to ain 1no-le!e on the !epen!ence o& the rate on the reactant concentrations. I(. Re)erences Theo!ore ". ro-n, et. al. Chemistry: The Central Science 6))th e!.7. 9earson E!ucation, 3nc., 2++B. 9rint. Chan, @a'mon!. Essential Chemistry . McGra->;ill Companies, )BB. 9rint.
The
3 here#' certi&' that 3 hae ien su#stantial contri#ution to this report.
Ca!eliña, "oren Ga#rielle
%&tana, Ma'neth (ince
Chem ).) Chemical Kinetics
9ae o&
