Question

75% of a zero order reaction complete in 4 h 87.5% of the same reaction completes in

• A. 6 h
• B. 12 h
• C. 8 h
• D. 2 h

Answer 1

Answer: (D)

$\text { For a zero order reaction rate }(k)=\frac{[A]}{t}-\frac{[A]}{t} $
$\text { where }[A]_{0}=\text { initial Conceatation } $
${[A]=\text { Concentration after time } t} $
$\text { when } 75 \% \text { of a zero order reaction Completes } $
$\text { then }[A]=\frac{75[A]_{0}}{100} $
$\text { time }=4 h r=4 \times 3600 sec$
$\text { reaction rate }(K)=\frac{(A]_{0}-\frac{75}{100}[A]}{4 \times 3600}=1.736 \times 10^{-5}[4]_{0} $
$\text { when }[A]=\frac{87.5}{100}[A]_{0} $
$\text { time } \equiv \frac{[A]_{0}-\frac{87.5}{100}[A] .}{1.736 \times 10^{-5}[A]_{0}}=7200.46 sec
=2 h$