The half-life of a substance in a first-order reaction is 15 minutes. The rate constant is:

2.46 × 102 min–1 4.62 × 10–2 min–1 3 × 10–5 min–1 3 × 10–9 min–1

4.62 × 10–2 min–1

Give, Half-life $= 15 min$ We know for a first order reaction, $t_{1/2} = \frac{0.693}{k}$ or, $k = \frac{0.693}{ t_{1/2}}$ $⇒k = \frac{0.693}{ 15}$ $⇒k = 0.462$ $⇒k = 4.62 × 10^{−2} min^{−1}$