Question

Match the following reaction orders with their units of rate constant:

Reaction Order	Units of k
(A) Zero order (B) First order (C) Second order	(I) L mol-1s-1 (II) mol L-1s-1 (III) s-1

Choose the correct option:

• A. A--II, B--III, C--I
• B. A--III, B--II, C--I
• C. A--I, B--II, C--III
• D. A--II, B--I, C--III

Hint:

The unit of rate constant for first-order reactions is always \(s^{-1}\), independent of concentration units.

Answer 1

The Correct Option is A

Concept: The units of rate constant depend on the order of reaction.

Step 1: Write the general rate equation.
\[ \text{Rate}=k[A]^n \] Units of rate are: \[ mol\,L^{-1}s^{-1} \]

Step 2: Find units for zero-order reaction.
For zero-order: \[ \text{Rate}=k \] Thus: \[ [k]=mol\,L^{-1}s^{-1} \] Hence: \[ A\to II \]

Step 3: Find units for first-order reaction.
For first-order: \[ k=\frac{\text{Rate}}{[A]} \] Units become: \[ s^{-1} \] Thus: \[ B\to III \]

Step 4: Find units for second-order reaction.
For second-order: \[ k=\frac{\text{Rate}}{[A]^2} \] Units become: \[ L\,mol^{-1}s^{-1} \] Thus: \[ C\to I \] Therefore, the correct matching is: \[ \boxed{A-II,\ B-III,\ C-I} \]