Question

The unit of rate and rate constant is same for which order of reaction?

• A. First
• B. Second
• C. Third
• D. Zero

Hint:

Unit of \( k \) is \( mol^{1-n}L^{n-1}s^{-1} \); set it equal to the rate unit \( mol\,L^{-1}s^{-1} \).

Answer 1

The Correct Option is D

Step 1: Tabulate the unit of \(k\) for each order using \(k=\text{rate}/[A]^n\) with rate fixed at \(mol\,L^{-1}\,s^{-1}\).
Step 2: Zero order (\(n=0\)): \(k = mol\,L^{-1}\,s^{-1}\). First order (\(n=1\)): \(k = s^{-1}\). Second order (\(n=2\)): \(k = L\,mol^{-1}\,s^{-1}\). Third order (\(n=3\)): \(k = L^{2}\,mol^{-2}\,s^{-1}\).
Step 3: Compare each entry with the rate unit \(mol\,L^{-1}\,s^{-1}\). Only the zero order entry is identical.
Step 4: Hence the rate and rate constant share the same unit for a zero order reaction.