Chemistry Reaction Kinetics SZABMU 2022
PMDC Verified Question 30 of 80
The unit of rate constant is the same as that of the rate of reaction in which of the following order of reaction:
A
Zero
B
Second
C
First
D
Third
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option A: Zero
Concept:

The units of the rate constant (\( k \)) are determined by the reaction order to ensure dimensional consistency with the reaction rate.

Formula:

$$ \text{Rate} = k[\text{Concentration}]^{n} $$

Solution:

  • For a zero-order reaction, the power \( n = 0 \).
  • $$ \text{Rate} = k[\text{A}]^{0} = k(1) = k $$
  • Because \( \text{Rate} = k \), \( k \) must inherit the exact units of rate: \( \text{mol dm}^{-3} \text{s}^{-1} \).


Why other options are incorrect:

In first order, \( k \) is in \( \text{s}^{-1} \). In second order, \( k \) is in \( \text{mol}^{-1}\text{dm}^{3}\text{s}^{-1} \). They do not match the rate units.

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