Question

For a first order reaction, the initial concentration of a reactant is 0.05 M. After 45 min it is decreased by 0.015 M. Calculate halfreaction time. $(t_{1/2})$

• A. 87.42 min
• B. 25.90 min
• C. 78.72 min
• D. 77.20 min

Answer 1

Answer: (A)

87.42 min

Answer 2

$k = \frac{2.303}{45} log \frac{0.05}{0.035}$
$k = \frac{2.303}{45} \times 0.1523 =0.00779$
$t_{1/2} = \frac{0.693}{0.00779} = 88.96 \, min$