Consider the following reaction 2X - -> Y + Z, when the concentration of X is doubled, the reaction rate increases by a factor of 4. What is the order of the reaction?

(A) zero order

(B) first-order

(C) second order

(D) third order

(C) second order

Explanation:

Let's consider the following reaction.

2X - -> Y + Z

The rate law is:

r = k. [A]ˣ

where,

r is the rate of the reaction

k is the rate constant

x is the reaction order of A

Let's assume x = 2. If the concentration of A is doubled, the new rate r₁ is:

r₁ = k. [2A]² = 4. k. [A]² = 4. r

The new rate r₁ is 4 times r when [A] is doubled. This happens when x = 2, that is, it is a second reaction order.