JEE PYQ: Chemical Kinetics Question 39
Question 39 - 2019 (11 Jan Shift 2)
The reaction $2\text{X} \to \text{B}$ is a zeroth order reaction. If the initial concentration of X is 0.2 M, the half-life is 6 h. When the initial concentration of X is 0.5 M, the time required to reach its final concentration of 0.2 M will be:
(1) 9.0 h
(2) 12.0 h
(3) 18.0 h
(4) 7.2 h
Show Answer
Answer: (3)
Solution
For the reaction $2\text{X} \to \text{B}$, follow zeroth order. Rate equation is $Kt = [\text{A}0] - [\text{A}]$. For the half-life: $t = t{1/2}$ and $[\text{A}] = 0.1$. $K \times t_{1/2} = 0.2 - 0.1$. $\frac{0.2 - 0.1}{6} = \frac{0.1}{6},\text{M hr}^{-1}$. Time required to reach from 0.5 M to 0.2 M: $\frac{0.1}{6} \times t = (0.5 - 0.2)$. $t = 18$ hours.
BETA
