Question

The overall order of a reaction is 2. The units of the rate constant for the reaction are ________.

a. 1/M
b. 1/s M⁻¹s⁻¹
c. M/s
d. s/M²

Answer 1

• M⁻¹s⁻¹

Step-by-step explanation:

You can infere the units of the rate constant for an overall order 2 reaction departing from the simplified case of a two identical reactants combined in a single elementary step:

• A + A → Products (single elementary step equation)

For that equation the differenttial form of the rate of reaction is:

• r = - d [A] / dt = K [A]²

The units of [A] are M¹ (i.e. M), and the units of - d [A] / dt are M¹ s⁻¹ . . . ( M stands for molar concentration)

Substituting the unis on both sides of the rate equation you get:

• M¹ s⁻¹ = K M²

Solving for K:

• K = M¹ s⁻¹ M⁻² = M⁻¹ s⁻¹, which is the final result.