Question

$75$% of a first order reaction was completed in $32$ minutes, then when was $50$% of the reaction completed?

• A. $4$ min
• B. $8$ min
• C. $24$ min
• D. $16$ min

Answer 1

The correct option is D $16$ min

For first order reaction:

$A=A_o{e}^{kt}$

$\ln \left(\frac{A_o}{A}\right)=kt$

$\frac{\ln \left(\frac{1}{0.25}\right)}{32}mi{n}^{-1}=k$

$\therefore t_{1/2}=\frac{ln2}{k}=\frac{ln2\times 32}{ln\frac{1}{0.25}}=16min$