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1、Reaction Kinetics (2) Xuan Cheng Xiamen UniversityPhysical Chemistry1Order Reaction Rate Lawt1/20A P1A P2A Pn2A PSimple Order ReactionsPhysical ChemistryReaction Kinetics2Typical Complex ReactionsPhysical ChemistryReversible reactionConsecutive reactionOpposing reactionCompeting reactionParallel rea
2、ctionkb(1)(2)(3)Reaction Kinetics3Physical Chemistry Reversible First-Order ReactionsConsider the reverse reaction (opposing reaction)kb(17.1)the first order in both forward and back directionsReaction Kinetics4Physical Chemistry(17.31)(17.32)Reversible First-Order ReactionsReaction Kinetics5Physica
3、l ChemistryAt equilibrium,Reversible First-Order Reactions(17.32)and(17.33)(17.34)Reaction Kinetics6(17.14)*(17.34)Physical Chemistry Reversible First-Order ReactionsA/AoC/Aokf / kb=2A CjtFig. 17.2When Aeq=0, kb=0A/AotFig. 17.1(a)Reaction Kinetics7Physical Chemistry Consecutive First-Order Reactions
4、Consider two consecutive irreversible first-order reactions(17.35)(17.36)Reaction Kinetics8Physical ChemistryLet only A be present in the system at t = 0 (17.37)Consecutive First-Order Reactions(17.38)(17.36)(17.11)(17.39)(17.40)Integration Reaction Kinetics?9Physical Chemistry Consecutive First-Ord
5、er ReactionsAt all times (conservation of matter)(17.38)(17.40)(17.41)Reaction Kinetics10Physical Chemistry Consecutive First-Order ReactionsThe intermediates concentration rises to a maximum, and then falls to zero The concentration of the product C rises from zero and reaches Ao(the position of ma
6、ximum: k1/k2)Reaction Kinetics?11Physical Chemistry Consecutive First-Order ReactionsSuppose that in an industrial batch process a substance A produces the desired product B which goes to decay to a worthless product C, each stage of the reaction being first-order. At what time will product B be pre
7、sent in greatest concentration?(17.40)The time dependence of BA maximum should occur at Reaction Kinetics12Physical Chemistry Consecutive First-Order ReactionsSince Ao 0, k1 0, soThe maximum concentration of BFor a given value of k1 k2, as k2 increases, both the time at which B is a maximum and the
8、yield of B increase.Reaction Kinetics?13Physical Chemistry Competing First-Order Reactions Consider two competing irreversible first-order reactions(17.42)ACDk1k2Parallel reactions(17.43)Reaction Kinetics14Physical Chemistry Competing First-Order Reactions(17.43)(17.11)Compare with(17.14)*For C(17.4
9、4)Reaction Kinetics?15Physical Chemistry Competing First-Order Reactionssimilarly(17.45)Division of (17.44) and (17.45)(17.44)(17.46)At any time during the reactionReaction Kinetics16Physical Chemistry Competing First-Order ReactionsConsider the reverse reactions(17.42)(17.47)MoreoverAt equilibriumThermodynamic control(17.46)Kinetic controlWhen any reverse reactions or interconversion of C and D can be neglectedReaction Kinetics17HomeworkPhysical ChemistryPage 591Prob. 17.13Supplemental Material Page 145, Prob. 16Page 149, Prob. 30Page 158, Prob. 68Reaction Kinetics18
