Question

Which of the following represents the expression for $\frac{3}{4}$th life of first order reaction?

• A. $\frac{2.303}{k}\log 4/3$
• B. $\frac{2.303}{k}\log 3/4$
• C. $\frac{2.303}{k}\log 4$
• D. $\frac{2.303}{k}\log 3$

Answer 1

The correct option is C $\frac{2.303}{k}\log 4$

Answer $C.$

The expression for rate of first order reaction,

$k=\frac{2.303}{t}\log \frac{a}{a-x}$

or $t=\frac{2.303}{k}\log \frac{a}{a-x}$ where $x=\frac{3}{4}a$

$t=\frac{2.303}{k}\log \frac{a}{a-\frac{3}{4}a}$

$=\frac{2.303}{k}\log \frac{a}{\frac{1}{4}a}$

$=\frac{2.303}{k}\log 4$