Question

A reaction is found to be second order with respect to reactant A. What would be the effect on the rate if the concentration of A were doubled?

A. The rate would be double
B. The rate would quadruple
C. The rate would decrease by half
D. The rate would increase in an unpredictable way
E. The concentration of A has no effect on the rate

Answer 1

For the second order reactions, the rate of the reaction $r$ is proportional to the square of the concentration of the reactant $[A]$ :

$r = -\frac{d[A]}{dt} = k·[A]^2$ .

Therefore, when the concentration of A is doubled, the rate would increase by 2²=4, so it would quadruple.

Answer: if the concentration of A were doubled, the rate would quadruple (B).