Question

The unit of rate constant is per second, the order of reaction is --

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

Hint:

For a quick check:
0th order: \( \text{mol L}^{-1} s^{-1} \)
1st order: \( s^{-1} \)
2nd order: \( \text{L mol}^{-1} s^{-1} \)

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
The unit of the rate constant ($k$) depends on the overall order of the reaction ($n$).
Step 2: Key Formula or Approach:
The general unit for the rate constant $k$ is given by:
\[ \text{Unit of } k = (\text{mol L}^{-1})^{1-n} \cdot s^{-1} \]
where $n$ is the order of the reaction.
Step 3: Detailed Explanation:
The given unit is "per second" or \( s^{-1} \).
Substituting the general formula:
\[ (\text{mol L}^{-1})^{1-n} \cdot s^{-1} = s^{-1} \]
For the term \( (\text{mol L}^{-1})^{1-n} \) to be equal to 1 (unity), the exponent must be zero.
\[ 1 - n = 0 \]
\[ n = 1 \]
This indicates a first-order reaction.
Step 4: Final Answer:
The reaction is of the first order.