The reaction A + 2B → products has been found to have the rate law, rate = k[A]2[B]. While holding the concentration of A constant, the concentration of B is increased from x to 3x. Predict by what factor the rate of reaction increases.

The rate of reaction triples up if the concentration of B is tripled.

Explanation:

The rate law is given as

r = k [A]² [B]

The rate is 2nd order with respect to [A] and first order with respect to [B]

If the concentration of A is held constant, the rate law can be written as

r = K [B]

where K = k [A]²

If initially the concentration of B is x

r = K [x]

If it is then changed to 3x, the rate becomes

r (new) = K [3x] = 3 K [x]

r (new) = 3 × r

Hence, the rate of reaction triples up if the concentration of B is tripled.