Chemistry Reaction Kinetics MDCAT 2016
PMDC Verified Question 68 of 80
The rate constant 'k' is 0.693 min\(^{-1}\). The half-life for the 1st order reaction will be:
A
0.693 min
B
1 min
C
4 min
D
2 min
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option B: 1 min
Concept:

For a first-order reaction, the half-life (\( t_{1/2} \)) is a constant value independent of initial concentration, mathematically derived from the natural logarithm of 2.

Formula:

$$ t_{1/2} = \frac{0.693}{k} $$

Solution:

  • We are given \( k = 0.693 \text{ min}^{-1} \).
  • Substitute this into the half-life formula:
  • $$ t_{1/2} = \frac{0.693}{0.693} $$
  • $$ t_{1/2} = 1 \text{ min} $$


Why other options are incorrect:

Failing to divide 0.693 by the rate constant or incorrectly multiplying them leads to the wrong numerical answers.

Quality & Fidelity Assurance: Every question on BeambePrep is rigorously curated against the official PMDC syllabus with zero filler, zero out-of-syllabus content, and zero typos. When an authentic past paper originally contained a historical mistake or ambiguity from the examining board (such as UHS or NUMS), BeambePrep faithfully reflects the original paper while detailing the nuance and scientific consensus in the autopsy above.

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