Question

If the half-life period of a first-order reaction is $138.6min$, then the value of decay constant for the reaction will be:

• A. $5{min}^{-1}$
• B. $0.5{min}^{-1}$
• C. $0.05{min}^{-1}$
• D. $0.005{min}^{-1}$

Answer 1

The correct option is D $0.005{min}^{-1}$

Rate constant for the first order reaction $=\frac{0.693}{\text{Half life}}=\frac{0.693}{t_{1/2}}$

$K=\frac{0.693}{t_{1/2}}=\frac{0.693}{138.6}=0.005mi{n}^{-1}$

Hence. option D is correct.