Consider the reaction and the initial concentration and initial rate data below.
ID: 984221 • Letter: C
Question
Consider the reaction and the initial concentration and initial rate data below.
BrO3-(aq) + 5 Br- (aq) + 6 H+(aq) ® 3 Br2 (aq) + 3 H2O (l)
Experiment
[BrO3-], (M)
[Br-],(M)
[H+],(M)
Initial Rate (M/sec)
1
0.10
0.10
0.10
1.2 x 10-3
2
0.20
0.10
0.10
2.4 x 10-3
3
0.10
0.30
0.10
3.5 x 10-3
4
0.20
0.10
0.15
5.4 x 10-3
Determine the rate law for this reaction
What is the overall order of the rate law?
Calculate the rate constant
Experiment
[BrO3-], (M)
[Br-],(M)
[H+],(M)
Initial Rate (M/sec)
1
0.10
0.10
0.10
1.2 x 10-3
2
0.20
0.10
0.10
2.4 x 10-3
3
0.10
0.30
0.10
3.5 x 10-3
4
0.20
0.10
0.15
5.4 x 10-3
Explanation / Answer
Let Rate = k [ BrO3-]^a [Br-]^b [H+]^c where a, b , c are respective orders
exp2 / exp1 = ( 2.4x10^-3) / ( 1.2x10^-3) = ( 0.2/0.1)^a
2 = 2^a , a= 1
exp 3/ exp 1 = ( 3.5x10^-3) / ( 1.2x10^-3) = ( 0.3/0.1)^b
3 = 3^b , b = 1
exp 4/exp1 = ( 5.4x10^-3) / ( 1.2x10^-3) = ( 0.2/0.1)^1 ( 0.15/0.1)^c
2.25 = 1.5^c , c = 2
Rate law is Rate = k [BrO3-] [Br-] [H+]^2
overall order is 1+1+2 = 4
from exp1 1.2x10^-3 = k ( 0.1) ( 0.1) ( 0.1)^2
k = 12 L^3 / ( mol^3 s)
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