Question

A reaction is second order with regard to a and first order with regard to b. The concentration of a is halved while the concentration of b is doubled. Which of the following is true?

1) The rate of the reaction will decrease
2) The rate of the reaction will increase
3) The rate of the reaction will remain the same
4) The rate of the reaction cannot be determined

Answer 1

When the concentration of A is halved and that of B is doubled in a reaction second order with regard to A and first order with regard to B, the reaction rate decreases by half.

Step-by-step explanation:

If a reaction is second order with regard to A and first order with regard to B, the rate law would be expressed as rate = k [A]² [B]. So, if the concentration of A is halved ([A] becomes [A]/2), the rate changes by a factor of (½)² = 1/4. If the concentration of B is doubled ([B] becomes 2[B]), the rate changes by a factor of 2¹ = 2. The overall effect on the rate is (1/4) × 2 = 1/2, which means the rate of the reaction will decrease to half of its original value.