Kinetics Solutions: #7

7.* (1995 3 6) The reaction between bromate ions and bromide ions in acidic aqueous solution is

BrO3-(aq) + 5Br- (aq) + 6H+ (aq) --> 3Br2(l) + 3H2O(l)

Using the data from 4 experiments shown below determine the orders of the rate of reaction for all three reactants, the overall reaction order, and the value of the rate constant k.

Experiment[BrO3-] (M) [Br-] (M)[H+] (M)rate (M/s)
1
0.100.100.108.0 x 10-4
2
0.200.100.101.6 x 10-3
3
0.200.200.103.2 x 10-3
4
0.100.100.203.2 x 10-3

Rate = k[BrO3-]a[Br-]b[H+]c

Compare: Experiment 1 and 2

Double [BrO3-], rate doubles, so first order in [BrO3-], a = 1

Compare: Experiment 2 and 3

Double [Br-], rate doubles, so first order in [Br-], b = 1

Compare: Experiment 1 and 4

Double [H+], rate quadruples, so second order in [H+]

Rate = k[BrO3-][Br-][H+]2 overall order = 1 + 1 + 2 = 4

To get k, simply plug in any value of the rate

Experiment 1: rate = 8.0 X 10-4 M/s = k(0.10 M)(0.10 M)(0.10 M)2

k = 8.0 M-3s-1

Note: M is mole / L