Question

Using the data, determine the rate constant of this reaction.
A+2B ---> C+D

trial     [A] (M)    [B] (M)   Rate (M/s)

1         0.290       0.260     0.0201

2         0.290      0.520      0.0201

3         0.580     0.260       0.0804

Number K=???
Units= ?? M.s-1, M-2s-1, s-1,M-1s-1

Answer 1

let the rate law be

rate = k [A]^a [B]^b

now

keep [B] constant , trail 1 and trail 3

we get

rate3 / rate1 = ( [A]3 / [A]1 )^a

0.0804 / 0.0201 = ( 0.58 / 0.29)^a

4 = ( 2)^a

a = 2

now

keep [A] constant , trail 1 and trail 2

we get

rate2 / rate1 = ( [B]2 / [B]1)^b

0.0201 / 0.0201 = ( 0.52 / 0.26)^b

1 = (2)^b

b = 0

so

the rate law is

rate = k [A]^2 [B]^0

rate = k [A]^2

now consider trail 1

0.0201 = k x [ 0.29]^2

k = 0.239

this is 2nd order

so

units of rate constant are M-1 s-1

so

the rate constant is 0.239 M-1 s-1