Question

75% of a first order reaction was completed in 32 minutes. When was 50% of the reaction completed

• A. 16 minutes
• B. 24 minutes
• C. 8 minutes
• D. 4 minutes..

Answer 1

Answer: (A)

16 minutes

Answer 2

$k=\frac{2.303}{t}log_{10} \left(\frac{a}{a-x}\right)$
$k=\frac{2.303}{t}log \left(\frac{100}{100-75}\right)....(i)$
$k= \frac{2.303}{t}log \left(\frac{100}{100-50}\right).....(ii)$
From the two eqns. (i) and (ii),
t = 16 minutes.