Chemistry Reaction Kinetics SET 2019
PMDC Verified Question 58 of 80
For the first order reaction, half-life is related to the expression t\(_{1/2}\)=0.693/k. Half-life is the:
A
Time taken for the concentration of the reactant to fall to half of its products value.
B
Time taken for the conc. of the product to the increase to half of its original value.
C
Time taken for the concentration of the reactant to fall to half of its original value
D
Time taken for the concentration of the reactant to fall to quarter of its original value
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option C: Time taken for the concentration of the reactant to fall to half of its original value
Concept:

The definition of half-life (\( t_{1/2} \)) is fundamental in chemical kinetics and radioactive decay.

Solution:

  • Half-life strictly measures the depletion of reactants, not the accumulation of products.
  • It is formally defined as the exact time required for the initial concentration of a reacting substance to be reduced to exactly 50% (one-half) of that initial value.


Why other options are incorrect:

Product concentration doesn't have an "original value" to fall from (it starts at zero). Falling to a quarter describes two half-lives.

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