Chemistry Reaction Kinetics ETEA 2024
PMDC Verified Question 10 of 80
For a first order reaction A \(\longrightarrow\) B, the rate constant is \( 0.0458 \text{ s}^{-1} \). Calculate rate of the reaction if the concentration of reactant is \( 0.35 \text{ mol dm}^{-3} \):
A
\( 0.012 \text{ mol dm}^{-3} \text{ s}^{-1} \)
B
\( 0.014 \text{ mol dm}^{-3} \text{ s}^{-1} \)
C
\( 0.016 \text{ mol dm}^{-3} \text{ s}^{-1} \)
D
\( 0.018 \text{ mol dm}^{-3} \text{ s}^{-1} \)
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Propolis Cognitive Error Autopsy

Official Correct Choice:
Option C: \( 0.016 \text{ mol dm}^{-3} \text{ s}^{-1} \)
Concept:

The rate of a first-order reaction is calculated by multiplying the rate constant by the reactant's instantaneous concentration.

Formula:

$$ \text{Rate} = k[\text{A}]^1 $$

Solution:

  • We are given the rate constant, \( k = 0.0458 \text{ s}^{-1} \).
  • We are given the reactant concentration, \( [\text{A}] = 0.35 \text{ mol dm}^{-3} \).
  • Substitute the values into the rate law:
  • $$ \text{Rate} = (0.0458) \times (0.35) $$
  • $$ \text{Rate} = 0.01603 \text{ mol dm}^{-3} \text{ s}^{-1} $$
  • Rounding to proper significant figures gives \( 0.016 \).


Why other options are incorrect:

The other options are mathematically incorrect products of the basic multiplication.

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