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)

$\text{ For a zero order reaction rate }(k)=\frac{[A]}{t}-\frac{[A]}{t}$
$\text{ where }[A{]}_0=\text{ initial Conceatation }$
$[A]=\text{ Concentration after time }t$
$\text{ when }75\%\text{ of a zero order reaction Completes }$
$\text{ then }[A]=\frac{75[A{]}_0}{100}$
$\text{ time }=4hr=4\times 3600sec$
$\text{ reaction rate }(K)=\frac{(A{]}_0-\frac{75}{100}[A]}{4\times 3600}=1.736\times 10^{-5}[4{]}_0$
$\text{ when }[A]=\frac{87.5}{100}[A{]}_0$
$\text{ time }\equiv \frac{[A{]}_0-\frac{87.5}{100}[A].}{1.736\times 10^{-5}[A{]}_0}=7200.46sec<br/><br/>=2h$