Question

The unit of velocity constant for first order reactions is:

• A. mol$^{-1}$ L s$^{-1}$
• B. mol L$^{-2}$ s$^{-1}$
• C. s$^{-1}$
• D. mol L$^{-1}$ s$^{-1}$

Hint:

Always use the formula $\text{Unit of k} = \text{mol}^{1-n} \, \text{L}^{n-1} \, \text{s}^{-1}$ to determine units of rate constants.

Answer 1

The Correct Option is C

Step 1: General formula for rate constant units.
For a reaction of order $n$: \[ \text{Unit of rate constant (k)} = \text{mol}^{1-n} \, \text{L}^{n-1} \, \text{s}^{-1} \]
Step 2: Apply for first order reaction.
For $n = 1$: \[ \text{Unit of k} = \text{mol}^{1-1} \, \text{L}^{1-1} \, \text{s}^{-1} = \text{s}^{-1} \]
Step 3: Conclusion.
Thus, the unit of velocity constant for a first-order reaction is s$^{-1}$.

Final Answer: \[ \boxed{\text{s}^{-1}} \]