Question

Identify the reaction order from each of the following rate constant:

(a) k = 2.3 × 10^-5 L mol^-1 s^-1

(b) k = 3 × 10^-4 4 s^-1

Answer 1

(a) k = 2.3 × 10^-5 L mol^-1 s^-1

We know that unit of k

= (mol L^-1)^1-ns^-1

where n is the order of reaction. 

Thus,

L mol^-1 s^-1 = (mol L^-1)^1-n s^-1

or L mol^-1 = (mol L^-11)^1-n

or (mol L^-1)^-1 = (mol L^-1)^1-n

Comparing powers on both sides

-1 = 1 – n

n = 1 + 1 = 2

i.e., the reaction is of second order.

(b) k = 3 × 10^-4 4 s^-1

s^-1 = (mol L^-1)^1-n s^-1

or (mol L^-1)⁰ s^-1 = (mol L^-1)^1-ns^-1

or (mol L^-1)⁰ = (mol L^-1)^1-n

Comparing powers on both the sides

0 = 1 – n

n = 1

i.e., the reaction is of first order.