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MUSI 132L - 01
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This 23 page Class Notes was uploaded by Kara Mayert on Sunday October 25, 2015. The Class Notes belongs to CHE111 at University of New England taught by JeromeMullin in Fall. Since its upload, it has received 21 views. For similar materials see /class/228650/che111-university-of-new-england in Chemistry at University of New England.
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Date Created: 10/25/15
Kinetics Rates and Mechanisms of Chemical Reactions 141 142 143 144 145 146 Photochemical Smog read on your own Reaction Rates Effect of Concentration on Reaction Rate The Rate Law and Its Components Reaction Mechanisms Reaction Rates Temperature and the Arrhenius Equation Catalysis Speeding Up a Chemical Reaction Fac ror39s ThaT AffecT Reac rion Rafe 1 Reac rivi ry of The r eac ran rs 2 Reac ran r Con rac r a homogeneous sys rems 1 gas phase 2 liquid phase 3 solid phase b he rer39ogeneous sys rems 1 rate oc area of phase in rer face 3 Concen rr a rions of r39eac ran rs Ra re Laws 4 Temperature As T gt reaction rate 5 Ca ralys rs MeasuremenT and Expression of ReacTion RaTes 1 Measure The decrease in reacTanT as funcTion of Time or 2 Measure The increase in producT as funcTion of Time 04 035 7 03 7 025 7 02 7 015 01 7 005 7 Concentration M 0 2 4 6 8 10 Time min In general for a reacTion of The form aA b8 9 cC The raTe of reacTion can be expressed as AZB gtABZ Concentration O I 0 2 4 6 8 10 time min A B A32 NOTE Express Rafe of reacTion in Terms of species wiTh coefficiem of 1 Expressing ReacTion RaTe conT39d 3 Measure Time iT Takes for a specific amounT of reacTanT To be used or Time iT Takes To produce a specific amounT of a producT gtshorTer Time fasTer raTe Average RaTe vs InsTanTaneous RaTe Because raTe of reacTion depends on reacTanT as reacTanT is consumed and reacTanT 4 Then raTe Average RaTe InsTanTaneous RaTe 910933 503 v 90033 93 933 gtltw30w n36 C4H9Cl M 03 0 x 000 000 005 00M N00 A00 39 m 000 000 Average Rafe C4H9Cl M 012 017 008 7 006 7 004 7 002 7 200 400 Time s 600 800 Ins ran raneous Rafe Rafe GT 1 Specific Poin r C4H9Cl 012 017 008 7 006 7 004 7 002 7 200 400 Time s 600 800 Ins ran raneous Ra re 012 Time s InsT Rafe Ms 01 0 210 x 10394 i 008 5o 190x10394 0067 100 160 x 104 g 004 200 135 x 10394 002 7 300 109 x 10394 400 800 x 10395 O o 260 460 600 800 Time s Dependence of Ra re on Reac ran r Concen rr a rion Rate Ms 000025 Ra re as freacfan rconC 00002 7 000015 7 00001 7 000005 7 0 0 002 004 006 008 01 reactant M 012 The Rafe Laws Ra re Law ma rhema rical expression r ela ring The rate of a r eac rion To The mutant concen rr a rions aAbBcC dD Ra re Law Reac rion Or39der39 aAbBcC dB The exponen rs in The Ra re Law are called The reaction ordersquot in each of The r39eac ran rs The example r eac rion is No res abou r Ra re Laws Reac rion order in any species usually is an in reger or half 12 32 can also be 0 Usually only reac ran rs appear in Ra re Law bu r some rimes produc rs do Overall reac rion order is sum of orders in each species Ra re Laws canno r be de rermined by i nspec rion ie canno r de rermine orders by knowing coefficien rs of balanced chemical equa rion Ra re Laws can be de rermined ONLY by Rafe Laws Examples 2N205g gt 4N02g 029 Rafe k N205 CHscHOQJ 39gt CH49CO9 Rate kCH3CHO32 H202GQ3I39GQ 2Haq 9 I393GQ 2H200 Rafe k H202 I39 Uni rs of The Ra re Cons ran r k As we have seen Ra res are expressed in uni rs of concen rr a rion per39 uni r Time eg M s1 or39 M min1 The uni rs of k depend on Overall Reac rion Or39der39 so Tha r Ra re always comes ou r To be M Time1 For39 a simple r eac rion aA bB or39 ANY o rher39 r39eac rion Over39all Or39der39 Ra re Law Uni rs of Ra re Cons ran r k 1ST Ra re 2quotCl Ra re 3rd Ra re e rc Determining Rate Laws Experimentally The Isolation Method Look at what happens to reaction rate when you change r39eactant concentr39ations one at a time i e want to isolate the effect of each r39eactant So carry out series of experiments under39 same conditions eg T but change one r39eactant concentration in each trial Measur39e reaction rate for39 each trial and deduce Rate Law Note Usually best to measure initial rate Example 1 DeTer39mining a RaTe Law DeTer39mine The RaTe Law of The r39eacTion below given The RaTe vs concenTr39aTion daTa in The Table A 28 C Tr39ial IniTiaI A IniTiaI B IniTiaI RaTe 1 0100 M 0100 M 550 x 10396 Ms1 2 0200 0100 220 x 10395 3 0400 0100 880 x 10395 4 0100 0300 165 x 10395 5 0100 0500 275 x 10395 6 0300 0100 495 x 10395 The In regr39a red Ra re Equa rions 1 Reactions Tha r are 13 or39der39 overall Consider a r eac rion GA 9 B Tha r is ls r order39 in A Rearranging and in regr a ring over39 The interval r0 ro r r ie from AO To AT First order reactions 04 First Order Reaction aA gt B 035 7 03 7 025 7 005 7 time min In A First Order Reaction aA gt B time mine Halflife The Time i r Takes To reduce r39eac ran r concen rr a rion ro half i rs ini rial value First Order Reaction Halflife 120 s 015 7 005 7 0 100 20039I 300 400 500 600 700 timesec Second Order Reactions aA B Second Order Reaction Second order Reaction A At O Mwbmm 0 200 400 600 time sec 0 200 400 600 time sec Chemical Thermodynamics Energy Changes in Chemical Sys rems gtConversion of energy from one form To ano rher gtTransfer of energy from one place To ano rher Why do we care abou r Thermodynamics gtPrac rical applica rions energy produc rion fuels amp foods energy conversion s rorage amp Transfer gtFundamen ral ro understanding mos r areas of chemis rry equilibrium kine rics elec rrochemis rry gtAows us To predic r reac rion spon ranei ry
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