Exam

NEET

Year

2005

Subject

Chemistry

Chapter

Chemical Kinetics

NEET 2005 · Chemistry · Chemical Kinetics

For a first order reaction A arrow B the reaction rate at reactant...

For a first order reaction $\mathrm{A} \rightarrow \mathrm{B}$ the reaction rate at reactant concentration of $0.01 \mathrm{M}$ is found to be $2.0 \times 10^{-5} \mathrm{~mol} \mathrm{~L}^{-1}$ $\mathrm{s}^{-1}$. The half life period of the reaction is:

Step-by-step solution

$$\begin{aligned}& \text{ rate of reaction }=2 \times10^{-5} \mathrm{~mol} \mathrm{~L}^{-1} \mathrm{~s}^{-1}\\ & \Rightarrow \text{ order of reaction is }n=1 \\ & \text{ rate }=\mathrm{K}[\mathrm{A}]^n \\ & {[\mathrm{~A}]}=0.01 \mathrm{M}\\ & \Rightarrow \quad \mathrm{K}=\frac{2 \times 10^{-5}}{0.01}=2 \times10^{-3} \\ & \mathrm{~K}=\frac{0.693}{t_{1/2}}\\ & t_{1/2}=\frac{0.693}{2 \times 10^{-3}}=346.5 \mathrm{~s} \end{aligned}$$Related Theory For a first-order reaction, a graph plotted with $\ln [A]$ on the $Y$-axis and time on the $X$-axis, will be a straight line with a slope of $-k$.