Unit 4 Chemical Kinetics (Intext Questions-1)
Intext Questions
4.1 For the reaction $\mathrm{R} \rightarrow \mathrm{P}$, the concentration of a reactant changes from $0.03 \mathrm{M}$ to $0.02 \mathrm{M}$ in 25 minutes. Calculate the average rate of reaction using units of time both in minutes and seconds.
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Answer
$ \text{Average rate of reaction}=-\frac{\Delta[\mathrm{R}]}{\Delta t} $
$=-\frac{[\mathrm{R}]_2- [\mathrm{R}]_1}{t_2-t_1}$
$=-\frac{0.02-0.03}{25} \mathrm{M} \mathrm{~min}^{-1}$
$=-\frac{-0.01}{25} \mathrm{M} \mathrm{~min}^{-1}$
$=4 \times 10^{-4} \mathrm{M} \mathrm{~min}^{-1}$
$=\frac{4 \times 10^{-4}}{60} \mathrm{M} \mathrm{s}^{-1}$
$=6.67 \times 10^{-6} \mathrm{M} \mathrm{s}^{-1}$
4.2 In a reaction, $2 A \rightarrow$ Products, the concentration of A decreases from 0.5 $\mathrm{mol} \mathrm{L}^{-1}$ to $0.4 \mathrm{~mol} \mathrm{~L}^{-1}$ in 10 minutes. Calculate the rate during this interval?
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Answer
Average rate $=-\frac{1}{2} \frac{\Delta[\mathrm{A}]}{\Delta t}$
$=-\frac{1}{2} \frac{[\mathrm{A}]_2-[\mathrm{A}]_1}{t_2-t_1}$
$=-\frac{1}{2} \frac{0.4-0.5}{10}$
$=-\frac{1}{2} \frac{-0.1}{10}$
$=0.005 \mathrm{~mol} \mathrm{~L}^{-1} \mathrm{~min}^{-1}$
$=5 \times 10^{-3} \mathrm{M} \mathrm{min}^{-1}$
