Question

Unit of rate constant for a zero order reaction is:

• A. mol/m$^2$·s$^{-1}$
• B. mol·s/m$^2$
• C. s$^{-1}$
• D. mol/m$^3$·s$^{-1}$

Hint:

For zero-order reactions, the rate is independent of concentration, so $k$ has units of concentration/time.

Answer 1

The Correct Option is D

Step 1: Recall the formula of rate law.
For a reaction of order $n$, the rate constant $k$ has units: \[ \text{Units of } k = \frac{\text{(concentration)}^{1-n}}{\text{time}} \]

Step 2: Substitute for zero order reaction ($n=0$).
\[ \text{Units of } k = \frac{\text{concentration}^{1-0}}{\text{time}} = \frac{\text{concentration}}{\text{time}} \]

Step 3: Express in standard SI units.
Concentration = mol/m$^3$, time = s \[ $\Rightarrow$ \text{Units of } k = \frac{\text{mol/m}^3}{s} = \text{mol·m$^{-3}$·s$^{-1}$} \]

Step 4: Conclusion.
The correct answer is (D).