Question

Karthik is carrying out a reaction with chemicals A and B according to the reaction, $(3A\to B)$. He wants to find the order of the reaction by changing concentration of A and observing the rate of the reaction. The first observation he made was by increasing the concentration of A 4 times after which, the rate of reaction doubled. Can you guess the order of reaction using Karthik’s experimental observation?

• A. 1
• B. 0.5
• C. 1.5
• D. 2

Answer 1

The correct option is B 0.5

As we know, Rate Equation $Rate=k[Reactant{]}^n$. where n is the order of the reaction.

Before Karthik changed the concentration, lets say concentration of reactant is a and rate of reaction is $r_1$.

As Karthik increased the concentration by 4 times, now the concentration is 4a and by his observation we know that rate is doubled, so now the rate is $2r_1$.

Substituting these in Rate equation. Before concetration change rate equation is
$r_1=[a{]}^n$ ….(1)
After concentration change rate equation is
$2r_1=[4a{]}^n$ ….(2)
Dividing Equation (2) with Equation (1)
$\frac{2r_1}{r_1}=[\frac{4a}{a}{]}^{n}2=[4{]}^n.\therefore n=\frac{1}{2}=0.5$
So order of the reaction = 0.5.