9 Physical Chemistry Let 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 ?
10 Physical Chemistry Consecutive First-Order Reactions At all times (conservation of matter) (17.38) (17.40) (17.41) Reaction Kinetics
11 Physical Chemistry Consecutive First-Order Reactions The intermediates concentration rises to a maximum, and then falls to zero The concentration of the product C rises from zero and reaches [A] o (the position of maximum: k 1 /k 2 ) Reaction Kinetics ?
12 Physical Chemistry Consecutive First-Order Reactions Suppose 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 present in greatest concentration? (17.40) The time dependence of [B] A maximum should occur at Reaction Kinetics
13 Physical Chemistry Consecutive First-Order Reactions Since [A] o 0, k 1 0, so The maximum concentration of B For a given value of k 1 > k 2, as k 2 increases, both the time at which [B] is a maximum and the yield of B increase. Reaction Kinetics ?
14 Physical Chemistry Competing First-Order Reactions Consider two competing irreversible first-order reactions (17.42) A C D k1k1 k2k2 Parallel reactions (17.43) Reaction Kinetics
15 Physical Chemistry Competing First-Order Reactions (17.43) (17.11)Compare with (17.14)* For C (17.44) Reaction Kinetics ?
16 Physical Chemistry Competing First-Order Reactions similarly (17.45) Division of (17.44) and (17.45) (17.44) (17.46) At any time during the reaction Reaction Kinetics
17 Physical Chemistry Competing First-Order Reactions Consider the reverse reactions (17.42)(17.47) Moreover At equilibrium Thermodynamic control (17.46) Kinetic control When any reverse reactions or interconversion of C and D can be neglected Reaction Kinetics