Question

What is the order of a reaction if the rate constant unit is \(L \cdot mol^{-1} \cdot s^{-1}\)?

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

Hint:

For reaction order \(n\): \[ k \propto (mol/L)^{1-n} \] Match the exponent to quickly determine the order.

Answer 1

The Correct Option is C

Topic - Chemical Kinetics (Rate Constant Units):
The units of the rate constant \(k\) vary depending on the overall order of the chemical reaction.
Step 1: Understanding the Question:
We are given the unit \(L \cdot mol^{-1} \cdot s^{-1}\) and asked to identify the corresponding reaction order \(n\).
Step 2: Key Formula or Approach:
The general unit for a rate constant of an \(n^{th}\) order reaction is: \[ \text{Unit} = (mol \cdot L^{-1})^{1-n} \cdot s^{-1} \] Step 3: Detailed Solution:
1. Given unit: \(L \cdot mol^{-1} \cdot s^{-1}\), which is equivalent to \((mol \cdot L^{-1})^{-1} \cdot s^{-1}\).
2. Compare the exponents of the concentration term \((mol \cdot L^{-1})\):
\[ 1 - n = -1 \] 3. Solving for \(n\):
\[ n = 1 + 1 = 2 \] 4. Therefore, the reaction is of the second order.
Step 4: Final Answer:
The reaction is second order.