Chem 162-2011 Lecture 5 2PLAN FOR TODAY: COMPLETE LECTURE 4 CHAPTER 13 (cont.) - CHEMICAL KINETICS H&P 13.7-13.8 •Collision theory •Effect of temperature on reaction rates
Chem 162-2011 Lecture 5 3FORMULASET: Rate = speed. Using a diagram with Y being 100 lbs and 110 lbs, and days 0 to 5, show that the increase in weight = slope = (Y2– Y1)/(X2– X1) = +2lb/day. Decrease in weight = -increase in weight = -slope = -(Y2– Y1)/(X2– X1) = -2lb/day. ET: Point out that table in middle of page contains the key formulas in kinetics. Discuss these formulas at beginning of recitation, focusing on 1oreaction. C12H22O11(sucrose) + H2O →2 C6H12O6(glucose) Rate of sucrose disappearance = -(∆[sucrose])/(∆time) = -([sucrosef] - [sucrosei])/(tf - ti) Rate of glucose appearance = 2 x Rate of sucrose disappearance aA + bB →cC + dD General rate of reaction = -(1/a)(∆[A]/∆t) = -(1/b)(∆[B]/∆t) = (1/c)(∆[C]/∆t) = (1/d)(∆[D]/∆t) Rate or a reaction may be written several ways. Reaction: 2A + 3B + C →2D Rate = -k[A]m[B]n[C]p∆C/∆t = -k[A]m[B]n[C]pd[A]/dt = -k[A]m[B]n[C]pIntegrated Reaction Differentiated rate law k OrderReaction Rate** RATE LAW***(y = mx + b)Half-life* units0 AvgRate = -(C2-C1)/(t2-t1) Rate = k[C]o=k [C]t= -kt + [C]ot1/2= [C]o/2k M1s-11 AvgRate = -(C2-C1)/(t2-t1) Rate = k[C]1ln[C]t= -kt + ln[C]ot1/2= 0.693/k Mos-12 AvgRate = -(C2-C1)/(t2-t1) Rate = k[C]21/[C]t= kt + 1/[C]ot1/2= 1/(k[C]o) M-1s-1** Rate of appearance = +slope; rate of disappearance = -rate of appearance = -slope. *** Differentiated Rate Law may be for more than one component, e.g., Rate = k[C]1[D]2*Half-lives: For a zero order reaction, each successive half-life is ½ the time of the preceding one. For a first order reaction, each successive half-life is equal in time to the preceding one. For a second order reaction, each successive half-life is double time of the preceding one. Arrhenius equation: k = Ae(-Ea/RT)A = frequency factor = combination of steric factor and collisional frequency Ea= energy of activation ln k2- ln k1= (-Ea/RT2) - (-Ea/RT1) ln k = -Ea/RT + ln Aln (k2/k1) = -(Ea/R)[(1/T2) - (1/T1)]
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