Question

Select the rate law that corresponds to the data shown for the following reaction:

Exp.	[A] mol dm−3	[B] mol dm−3	Initial Rate mol dm−3
1.	0.012	0.035	0.10
2.	0.024	0.070	0.80
3.	0.024	0.035	0.10
4.	0.012	0.070	0.80

Options

• Rate = k[B]³

• Rate = k[B]⁴

• Rate = k[A] [B]

• Rate = k[A] [B]³

Answer 1

Rate = k[B]³

Explanation:

When the concentration of B remains constant while the concentration of A varies, the rate of the reaction remains constant, as shown in experiments 1 and 3 or 2 and 4. As a result, the pace of the reaction is independent of A concentration. The rate of the reaction increases from 0.1 to 0.8 when the concentration of A is kept constant and the concentration of B is doubled, as shown in experiments 1 and 4. The new rate is eight times higher than the previous one. Hence The reaction rate is proportional to the cube of the concentration of B. (∵ 2³ = 8)

Hence, the rate law is rate = k[B]³