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Question 11 Mark
For the reaction R → P, the concentration of a reactant changes from 0.03M to 0.02M in 25 minutes. Calculate the average rate of reaction using units of time both in minutes and seconds.
Answer
Average rate of reaction
$=-\frac{\triangle[\text{R}]}{\triangle\text{t}}$
$=-\frac{[\text{R}]_2-[\text{R}]_1}{\text{t}_2-\text{t}_1}$
$=-\frac{0.02-0.03}{25}\text{M mim}^{-1}$
$=-\frac{-0.01}{25}\text{M mim}^{-1}$
$= 4 × 10^{-4}\ M\ min^{-1}$
$=\frac{4\times10^{-4}}{60}\text{M s}^{-1}$
$= 6.67 × 10^{-6}\ Ms^{-1}$
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Question 21 Mark
For a reaction, $\mathrm{A}+\mathrm{B} \rightarrow$ Product; the rate law is given by, $\mathrm{r}=\mathrm{k}[\mathrm{A}]^{1 / 2}[B]^2$. What is the order of the reaction?
Answer
The order of the reaction is sum of the powers on concentration.
So that sum will.
$r=k[A]^{1 / 2}[B]^2$
Order of reaction $= 12 + 2 = 2.5.12 + 2 = 2.5.$
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Question 31 Mark
In a reaction, $2 \mathrm{~A} \rightarrow$ 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?
Answer
$\text{Average Rate}=\frac{-1}{2}\frac{\triangle\ [\text{A}]}{\triangle\ \text{t}}=\frac{-1}{2}\frac{\text{[A]}_2-\text{[A]}}{\text{t}_2-\text{t}_1}$
$=\frac{-1}{2}\frac{(0.4-0.5)}{10}=\frac{-1}{2}\frac{(-0.1)}{10}$
$ =5 \times 10^{-3} \mathrm{M} \mathrm{~min}^{-1}$
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Question 41 Mark
Define 'order of a reaction'.
Answer
The sum of powers of the concentration terms of the reactants in the rate law expression is called the order of that chemical reaction.
Alternate answer
rate $=k[A]^p[B]^q$
Order of reaction = P+q.
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Question 51 Mark
Why is it that instantaneous rate of reaction does not change when a part of the reacting solution is taken out?
Answer
Instantaneous rate is measured over a very small interval of time, hence, it does not change when a part of solution is taken out.
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Question 61 Mark
Write the rate equation for the reaction $2\text{A + B}\xrightarrow{\ \ \ \ \ \ }\text{C}$ if the order of the reaction is zero.
Answer
Rate $=k[A][B]^0$ or Rate $=k$.
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