Question

The order of reaction for which the unit of the velocity (rate) constant is \(mol\,L^{-1}\,s^{-1}\) is:

• A. First order
• B. Second order
• C. Zero order
• D. None of these

Hint:

Use \(k\) unit \(= mol^{(1-n)}L^{(n-1)}s^{-1}\). When rate \(=k\), the order is zero.

Answer 1

The Correct Option is C

Step 1: Think about zero order directly. A zero-order reaction has rate independent of concentration: \(\text{rate}=k[A]^0=k\).
Step 2: Match units. If rate \(=k\), then \(k\) must carry the same units as rate, namely \(mol\,L^{-1}\,s^{-1}\). That is exactly the unit given in the question.
Step 3: Eliminate. First order gives \(k\) in \(s^{-1}\); second order gives \(k\) in \(L\,mol^{-1}\,s^{-1}\). Both differ from the stated unit, so option (iv) is not needed either.
Step 4: Answer. The order is zero.
\[\boxed{\text{Zero order}}\]