Concept of Order of Reaction

Question

For a given reaction, !!t_(1//2)= 1/(ka^2)!!. The order of this recation is:

(a) 2

(b) 3

(c) 1

(d) 0

Solution

The relationship between half life and initial concentration is given as:

!!t_(1/2) prop 1/(a\^(n-1))!!

Where n= order of reaction.

Here we have

!!t_(1/2) prop 1/(a^2)!!

Thus by comparing:

!!a\^(n-1)=a\^2!!

!!n-1=2!!

!!n=3!!

Hence it's a third order reaction.

Therefore option (b) is correct.