Question

If the initial concentration is reduced to 1/4th in a zero order reaction, then the time taken for half the reaction to complete:

• A. remains same
• B. becomes 4 times
• C. becomes one-fourth
• D. doubles

Answer 1

Answer: (C)

becomes one-fourth

For a zero order reaction, $t_{1/2}=\frac{[A{]}_0}{2k}$
Let $[A{]}_0=a$
$t_{1/2}=\frac{a}{2k}$ ......(1)
When the intial concentration is reduced to one fourth, $[A{]}_0=\frac{1}{4}\times a.$
$t_{1/2}^{\prime }=\frac{\frac{1}{4}\times a}{2k}$ ......(2)
By dividing equation (2) by (1), we get
$\frac{t_{1/2}^{\prime }}{t_{1/2}}=\frac{\frac{\frac{1}{4}\times a}{2k}}{\frac{a}{2k}}=\frac{1}{4}$

Hence, option C is correct.