Question

For a first order reaction, $t_{0.75}$ is 138.6 seconds. Its specific rate constant (in $s^{-1}$) is:

• A. ${10}^{-2}$
• B. ${10}^{-4}$
• C. ${10}^{-5}$
• D. ${10}^{-6}$

Answer 1

The correct option is A ${10}^{-2}$

We know that:
Half life for first order reaction $=\frac{0.693}{k}$
and
$t_{\frac{1}{2}}=\frac{1}{2}\times t_{0.75}$
$\frac{0.693}{k}=\frac{138.6}{2}$
$k={10}^{-2}$