Presentation is loading. Please wait.

Presentation is loading. Please wait.

1 Reaction Kinetics (2) Xuan Cheng Xiamen University Physical Chemistry.

Similar presentations


Presentation on theme: "1 Reaction Kinetics (2) Xuan Cheng Xiamen University Physical Chemistry."— Presentation transcript:

1 1 Reaction Kinetics (2) Xuan Cheng Xiamen University Physical Chemistry

2 2 OrderReactionRate Lawt 1/2 0 A P 1 2 n 2A P Simple Order Reactions Physical Chemistry Reaction Kinetics

3 3 Typical Complex Reactions Physical Chemistry Reversible reaction Consecutive reaction Opposing reaction Competing reaction Parallel reaction kbkb (1) (2) (3) Reaction Kinetics

4 4 Physical Chemistry Reversible First-Order Reactions Consider the reverse reaction (opposing reaction) kbkb (17.1) the first order in both forward and back directions Reaction Kinetics

5 5 Physical Chemistry (17.31) (17.32) Reversible First-Order Reactions Reaction Kinetics

6 6 Physical Chemistry At equilibrium, Reversible First-Order Reactions (17.32) and (17.33) (17.34) Reaction Kinetics

7 7 (17.14)* (17.34) Physical Chemistry Reversible First-Order Reactions [A]/[A] o [C]/[A] o k f / k b =2 A C jt Fig When [A] eq =0, k b =0 [A]/[A] o t Fig. 17.1(a) Reaction Kinetics

8 8 Physical Chemistry Consecutive First-Order Reactions Consider two consecutive irreversible first-order reactions (17.35) (17.36) Reaction Kinetics

9 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 10 Physical Chemistry Consecutive First-Order Reactions At all times (conservation of matter) (17.38) (17.40) (17.41) Reaction Kinetics

11 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 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 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 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 15 Physical Chemistry Competing First-Order Reactions (17.43) (17.11)Compare with (17.14)* For C (17.44) Reaction Kinetics ?

16 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 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

18 18 Homework Physical Chemistry Page 591 Prob Supplemental Material Page 145, Prob. 16 Page 149, Prob. 30 Page 158, Prob. 68 Reaction Kinetics


Download ppt "1 Reaction Kinetics (2) Xuan Cheng Xiamen University Physical Chemistry."

Similar presentations


Ads by Google