The half life of a first order reaction with K value 6.93 × 1014 s–1 is
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → 10-15 s
For a first order reaction, the half-life does not depend on the initial concentration:
\( \displaystyle t_{1/2} = \frac{0.693}{k} \)
With k = 6.93 × 1014 s−1:
\( \displaystyle t_{1/2} = \frac{0.693}{6.93 \times 10^{14}\ \mathrm{s^{-1}}} = 0.1 \times 10^{-14}\ \mathrm{s} = 1 \times 10^{-15}\ \mathrm{s} \)
Shortcut: A half-life is a time, so its unit is s; Option (1), in s−1, is ruled out. A very large k means a very short half-life, which rules out Options (2) and (4).