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# General Chemistry II CHE 114

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This 79 page Class Notes was uploaded by Jerrell Fritsch on Sunday October 25, 2015. The Class Notes belongs to CHE 114 at University of North Carolina at Greensboro taught by Edwar Shamshoum in Fall. Since its upload, it has received 779 views. For similar materials see /class/229068/che-114-university-of-north-carolina-at-greensboro in Chemistry at University of North Carolina at Greensboro.

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Date Created: 10/25/15

KINETICS AND EQUILIBRIUM a39ut Chemis hve Soluons Kinetics and equilibrium Dr Ed Shamshoum REACTION RATES Ar 2quot 39lg d Kinetics and equilibrium Dr Ed Shamshoum Chemical Kinetics Deals with the speed at which the concentrations of the reactants and products changes occur The SPEED or RATE of a process is de ned as the change in a given quantity over a speci c period of time For chemical reactions Reaction rate is the change in concentration of a reactant or Kinetics and equilibrium Dr Ed Shamshoum Kinetics Experimentally it is shown that there are 4 factors that in uence the speed of a reaction nature of the reactants temperature catalysts concentration 4 Tro chemistry A moleeular V 7 Approach Reaction Rates Concentration of A at time to Concentration of A at time t 1 e 2 t2 zl Where A is the reactant or product indicate concentration in moiL A is change in given quantity Ts TV 7 i nk IIIAmHX Kinetics and equilibrium Dr Ed Sha r nshoum REACTION RATES Reaction rate is change in conc Of reactants or products as a function of time A gtB Reaction rate AAAt or ABAt Negative sign because A is decreasing Once the rate of one reactant or product has been determined the rates of other substances can be k a 3 r 1 f Kinetics and equilibrium Dr Ed 39Sh a r39n shoum Awerage Rate between two points AAAt Concentration Reactant A Product B time tel I I g d Kinetics and equilibrium Dr Ed Shamshoum Hypothetical Reaction Red gt Time Number Number sec Red Blue 1nth1s reaction 100 0 one molecule of Red turns 84 16 into one molecule of 10 71 29 the number of molecules 15 59 41 will always total 100 20 50 50 25 42 58 the rate of the reaction can 30 35 65 be measured as the speed of 35 30 70 loss of Red molecules Number of Molecules Concentration vs Time for Red gt Blue Number Red Number Blue Tim e sec L39 m r 2 w egg21 l if V Diva rtquot if L I LL JD 1 J 21 ii 1 a The number ef melee of A and B plotted we time Change in reactants Decrease w time At beginning of rexn 397 1 V mm A is at maximum M A j i And Pr 1 at zero D H mm 033 m 3 m T5 V E 15 i 51 i a 3 3 3925 mu 1 3 027 F Cl 1395 1 I I Ii G en 43 50 En Time min Kinetics and equilibrium Dr Ed Shamshoum Relative Rates 39 2N205g 4N02 02g AN205AT 7 AN02AT AOzAT These rates are not equal to each other because the coef cients are not the same To correct for this we use the inverse of the coef cients In the chemical equation quotv 3 f 5 Kinetics and equilibrium Dr Ed 39Sha mshoum RATES cont 0A2B C One molecule of A reacts with 2 molecule Of B to produce 1 molecule Of C This shows that B reacts twice as fast as A The rate AAAt l2ABAt ACAt It can also be written as 3H 3 inetics and equilibrium Dr Ed 39Sh a r39n shoum REACTION RATES Let slook at aAbBcC gtdDeEfF i AM 1AB 1 AC 1 AD Rate a At b At c At d At Eben MAM 0395 Mmm If we know the rate at any One point of a substance We can calculate rate of Change Of any other substance ABAt 05 ba ACAt 05 ca ADAt 05 da 0 And so on Rates are typically expressed as Molarity per second or per unit time Ms A 39 AV qx j l JD 9 quot S quot1 Kinetics and equilibrium Dr Ed Shamshoum Average Rate the average rate is the change in measured concentrations in any particular time period linear approximation of a curve the larger the time interval the more the average rate deviates from the instantaneous rate Use Graph to Calculate Average Rate of Reaction H2 12 92HI Average Rate in a certain time interval is calculated Concentration of A at time to Concentration of A at time t1 6 t2 l1 Concentration vs Time for H2 12 gt 2H1 2000 7 1800 7 1 1600 7 1400 7 1200 7 0800 7 concentration M 0600 7 0400 7 0200 7 10000 20000 30000 40000 50000 60000 70000 80000 90000 100000 time s 30 N029 NQ 12 02 Time N02 M 7 77 0 100 V 7V W 20 0904 amp 20 s and between 50 30 0860 amp 60s 40 0818 B What is the rate of 50 0778 formation of O2 60 0740 AW MO 70 0704 3 Rate 2 T22A Z 80 0670 b 47x10 3M 2 235x10 3 90 0637 S A A S 100 M 0606 b 38x10 3M 2 19x10 3 39 lt J by S a Use the graph to calculate the following The average rate of the reaction between 0 and 25s The instantaneous rate of the reaction at 25s Instantaneous rate of formation of HBr at 50s b Make a rough sketch of a curve representing the concentration of HBr as a function of time Assume that the initial concentration of HBr is zero Kinetics and equilibrium Dr Ed Shamshoum Problem 31 Solution Extract the information you need from the graph of BIZ VS times 39 131 2 gt3 V l I r l7 Kineties ahdzequmbriu m39 Dr Ed Instantaneous Rate the instantaneous rate is the change in concentration at any one particular time slope at one point of a curve 0 determined by taking the slope of a line tangent to the curve at that particular point rst derivative of the function for you calculus fans Concentration M r 40 60 80 100 120 Hr Hf Wz af 9r Time s 7 Copyright 2008 Pearson Prentice Hall Incr Instantaneous Rate Instantaneous rate at f 0 initial rate K At t 0 Initial rate W 2x104 M 39 Ax 200s 0s s X k 0017M 0042M An 500s Rate 658x10 5 M 780s 400s s Instantaneous rate at It 2 600 s 100 200 300 400 500 800 73900 800 900 Time 8 000 M to 0868 M in the rst 10 s Calculate the average rate in the rst 10 s and the AH H202 W 3 I iEX 131 For the reaction given the 1 changes from on 2 H mm gt 13 mm 2 H200 Solve the equation for the Rate in terms of the change in concentration of the Given quantity E At 4140 X10quot3 3 Rate1j AI 1 0868M 1000 M 105 Solve the equation of the Rate in terms of the change in the concentration for the quantity to Find for H 2440 gtlt10393 M 880 gtlt10393 M 39 39 s 5 Rate AH 2 At AH At 2Rate Measuring Reaction Rate ou need to be able to measure the concentration of at least one component in the mixture at many points in time There are two ways of approaching this problem l for reactions that are complete in less than 1 hour it is best to use continuous monitoring of the concentration or 2 for reactions that happen over a very long time sampling of the mixture at various times can be r v 1 A actors Affecting Reaction Rates What produces more effective collisions between reactant molecules 1 Temperature 2 Concentration of Reactants 3 Structure or Orientation of Reactants 4 Surface Area 5 Catalysts Kiri tiCS a d fquilib ritjfn v Dr Ed 39S quot f i fmi a Reactants b Absorbed c No it could also revert back to the reactants wilitmpiucudwbim Energy Diagram number of mommies ac ua on Energy 1 Kinetics and equilibrium Dr Ed Shamshoum FACTORS ON KINETICS To Get More Effective Collisions a Concentration of Reactants Increase in conc Generally increases rate Reactants MUST collide before they react Increase in frequency of collisions In gaseous system increase in pressure gets reactants closer to each other thus increase of collisions am 3 Kinetics and equilibrium Dr Ed 39Sh a r39n shoum FACTORS ON KINETICS To Get More Effective Collisions 1 Or lin T Changes The shape Of curve b Temperature Increase in temperature increases speed and thus increase the kinetic energy of particles Particles with more kinetic energy have a better chance of overcoming the energy of activation barrier Kinetics and equilibrium Dr Ed Shamshoum FACTORS ON KINETICS To Get More Effective Collisions c Nature of Reactants In a reaction bonds are broken and new ones formed Ease or difficulty of bond breaking and bond formation Reactions that involve the breaking of bonds tend to be slow at room temperature am 3 Kinetics and equilibrium Dr Ed 39Sh a r39n shoum Factors Affect Reaction Rates d Orientation ofCollisns HCl approaching ethylene A 7 Viewquot 51 J c x r i iquot 39 1 Kinetics and equilibrium Dr Ed Shamshoum FACTORS ON KINETICS To Get More Effective Collisions e Surface Area Increase in surface area increases the number of collision sites Smaller Zinc particles react faster with HCl than larger particles 75 45 J W39JEKx Kinetics and equilibrium Dr Ed Shamshoum FACTORS ON KINETICS To Get More Effective Collisions 0 f Catalysts Catalyst is a substance that reduces the energy of activation for a chemical reaction Without being consurnecliin the reaction 39 eaciion Wit out caia ysi 75 M J W39JEKx Kinetics and equilibrium Dr Ed Shamshoum REACTION RATES When studying chemical reactions at constant temperature rates can be determined by varying the concentration of one reactant while holding the other s constant Kinetics and equilibrium Dr Ed Sh a r39n Shoum Simple Research When studying kinetics or anything else the researcher changes one variable at a time 0 Changing too many variables at a time lead to false conclusions Two Types of Rate Laws 0 Differential Rate Law The rate Law shows how rate depends on concentrations 0 Integrated Rate Law Shows how the concentration of species in reaction Kinetics and equilibrium Dr Ed Shamshoum STUDYING RATE LAWS When studying reaction rates conditions are chosen Where the reverse reaction is considered negligible Rate kreactantr1 It shows that rate dependant on conc of reactants k is a proportionality constant n is reaction order and MUST be determined quota 3 f Kinetics and equilibrium Dr Ed Sha r nshoum Rate law Initial Consider aAbB CC dD Rate Law has the form Initial Rate 1ltAHBm Note that exponents are not stoichiometric quot en 39 Ire 1 I 1 Kinetics and equilibrium Dr Ed 39Sh a r39n shoum Rate Order 0 Initial Rate 1A Bm Reaction order 11 order for A and m order for B The overall reaction order is n m a a rquot Kinetics and equilibrium Dr EdVSha rh Shoum Rate Order Practice Rexn order is exponent in rate law What is the Lder of each reactant and overall order for the following reactions 2H2 02 ZHZO RatekH202 Rate kC122 2P 3C12 213313 1 I 1 Kinetics and equilibrium Dr Ed 39Sh a r39n shoum Rates How do we explain these rates RatekH2Oz 1st order in each Rate kC122 2nd order in C12 Zero order in P Rate kHClNH32 lst order in HCl and 2rld order y 39 17 Dr Ed Sh F ho m Kinetibs ahd equilibrium III IIi I IiHi MW 7 HI J L W1 Reactant Concentration versus Time Rate is constant because Reaction does not slow a Down as concentration i decreases 1 I Second order n 2 Rate First order w n 1 Zero order n I 0 0 I I O 20 40 60 80 100 120 Time s Reactant Concentration versus Time Decrease in conc not linear Rate is directly proportional to Concentration of reactants i Rate Slows down MS With time First order n 1 I i I I I 0 20 40 60 80 100 20 Time Doubling conc Doubles the rate A Kinetics and equilibrium Dr Ed Shamshoum Reactant Concentration versus Time 1 I 02 Second order n 2 2 First order n 1 Zero order n 0 I I I I 20 40 60 80 Time s I 100 120 Rte kA2 Rate is proportional to The square of the concentration Of reactant Kinetics and equilibrium Dr Ed Shamshoum EXAMPLE OF REACTION ORDER CALCULATIONS Determining the Rate Law can only be determined experimentally graphically rate slope of curve A vs time if graph A vs time is straight line then exponent on A in rate law is 0 rate constant slope if graph 1nA vs time is straight line then exponent on A in rate law is 1 rate constant slope if graph 1 A vs time is straight line exponent on A in rate law is 2 rate constant slope initial rates y mpa l m Chemistry Aquot molecular 7 Approach Example 1 A 9 Prod A M Initial Rate Visual Inspection Rate W5 is 1st order because doubling cone Doubles 0010 0015 the rate Rate kA1 020 003 RatekA 0540 106 k Rate A K 0015010 015 s41 Example 1 A 9 Prod A M Initial Rate Visual Inspection Rate WS is Zero order because changing conc Has no 003910 039015 effect on rate Rate kAO 020 0015 RatekAO 040 0015 k Rate llt 0015MS391 NHZWQHNOSWI gtN2g 211200 i1 00050 135X10397 0010 270X10397 0010 540X10397 ANH Rate T 1n and n can be determined by Watching how initial Rates depend on initial concentrations Kinetics and equilibrium Dr Ed VSh a r39n shoUm irst Visual Inspection of Rates When comparing Run 1 and 2 When NO2 is doubled while holding NH4 constant the Initial rate doubled This means that reaction is First order for N02 Kinetics and equilibrium Dr Ed Shamshoum By Initial Rates Calculations Ra 27x10 7Ms Rate 1 k0100M 0005 20171 all RWLWH4W0239 Kinetics and equilibrium Dr Ed Shamshoum Reaction Order Calculations A B C Products Run A0 B0 C0 Initial Rate 1 0151 M 0213 M 0398 M 0480 Ms 2 0251 M 0105 M 0325 M 0356 Ms 393 0151M 0213M 0525M 1102Ms Kinetics and equilibrium Dr Ed Shamshoum How do we determine order First let s assume the order for the reactants is Rate k A BbCc Second Isolate the effect of Conc of one of the reactants Say Run I vs Run 3 So the raio of Initial Rate of 1 vs calculate c 0480 Ms W Mb0398Mc 0 KWWmssty 1102 Ms 04356 g0398MC 07581C 0525MC Kinetics and equilibrium Dr Ed Sha r nshoum Order Calculations Cont To calculate b we need to pick 1 VS 4 0480Ms L1541 0213Mb0398M3 0988Ms k 1Ma0250Mb0480M3 So 04858 08520b05701 quota 3 f Kinetics and equilibrium Dr Ed 39Sha mshoum Order Calculations Cont To calculate a Choose 1 vs 2 0480Msll40151Ma0213M1O398M3 0356Ms 40251Ma0100M10325M3 13483 06016a202861122463 111 03619 a 111 06016 i J 3 VI Kinetics and equilibrium Dr Ed 39Sh a r39n shoum Integrated Rate Law We just looked at Rate of reaction vs concentration But What about the relationship between concentration of reactants and time Kinetics and equilibrium Dr Ed Il SH ia39ir 39ho m 39 Zero Order Reactions M 2 Rate kAO k At A A10 kt AL kr A10 0 graph of A vs time is straight line With slope k and yintercept A0 0 when Rate Msec k Msec alf life for Zero Order Reaction Half life t 12 of a reaction is the time required for the concentration of a reactant to fall to one half of its initial value A k1 Mo 1 At tlZ Air 2 7 Aio J N 39 Kineti Cs ahdzequmbriu m Dr Ed First Order Integrated U sin g Calculus the equation is integrated L4AL ML k 81103 k Y mx b a LnA LniAio kt Ln A kt time A 0 Kinetics and equilibrium Dr Ed Shamshoum HalfLife 0 the g5 I a ofa reaction is the length 7 7 of time it takes for the 33 concentration of the reactants to fall to 12 its initial value the halflife of the reaction depends on the order of the reaction Half Life for a FirstOrder Reaction After 1 halflife After 2 halflives After 3 half lives 5 9 H 71 a H s W U C O U HalfLife for a FirstOrder Reaction At to For a rst order reaction the half life is constant and independenl of concentration After 1 halflife J a A erZhaIflives gt J L 0 A 075 7 a a a E u After3 halflives 1 E E E 050 I 0 Ln 3 0 2 12 025 I k 000 t 1 fll H 0 0 100 200 300 39 Time s k Copyright 2008 Pearson Prentice Hall Inc First Order 12 life t1 2 is independent of initial concentration Constant half life is unique to rst order reaction If initial concentration is 1M at t12 the concentration Is reduced to 05M and then every half life will be reduced By 50 quota 3 f Kinetics and equilibrium Dr Ed 39Sha m shoum Rate Data for C4H9C1 H20 gt C4H90H HC1 Time sec C 4H9Cl M 00 01000 500 00905 1000 00820 1500 00741 2000 00671 3000 00549 4000 00448 H9CI H20 C4H9OH 2 7 H mm V C T mm Fm WWW Cailawj lma LNC4H9C1 vs Time for Hydrolysis of C4H9C1 A c o 2 m c a 0 c o 0 V Z 7K i 400 E time s Second Order Reactions Rate kA2 1A kt 1AO graph 1 A vs time gives straight line with slope k and yintercept 1 A0 used to determine the rate constant t12 1kle when Rate Msec k M39lseC391 1A IAJQ Rate Data For Partial Pressure Time hrs N02 mmHg 1nPN02 1PN02 0 1000 4605 001000 30 625 4135 001600 60 455 3817 002200 90 357 3576 002800 120 294 3381 003400 150 250 3219 004000 180 217 3079 004600 210 192 2957 005200 240 172 2847 005800 Partial Pressure N02 mmHg vs Time Pressure mmHg lnPN02 vs Time A B a 8 L1 Q V H 1N EWDWTEDM QC 0 g g big 350 TABLE 132 Rate Law Summary Table Rate Units Integrated StraightLine HalfLlfe Order Law ofk Rate Law Plot Expression y intercepl AL lt t A10 2 1 AL 0 Rate kA M61 M1 kH M0 g Slope 7k 2 2k k 2 gt Time t A In A kl lnA L L yintercept lnA0 0693 1 1 Rate kA39 s 1 E 11 k k 0693 A Slope k In kr Mu gt Time t A 1 1 2 Slope k l 1 l l I l l 2 Rate HAZ M s A k A10 2 2 MAL k A yintercept 1 A gt Time t Copyright 2008 Pearson Prentice Hall Inc

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