Explain the difference between instantaneous rate of a reaction and average rate of a reaction.
The difference between instantaneous rate of reaction and average rate of a reaction are as below
| Instantaneous rate of reaction | Average rate of reaction | |
|---|---|---|
| (i) | It occurs within a short span of time. | It occurs during a long interval of time. |
| (ii) | It can't be calculated for multistep reaction. | It can be calculated for multistep reaction. |
| (iii) | It can be calculated for elementary reaction. | It can be calculated for elementary reaction. |
With the help of an example explain what is meant by pseudo first order reaction.
A reaction in which one reactant is present in large amount and its concentration does not get altered during the course of the reaction, behaves as first order reaction. Such reaction is called pseudo first order reaction.
e.g., (i) hydrolysis of ethyl acetate
$$\text { Rate of reaction }=k\left[\mathrm{CH}_3 \mathrm{COOC}_2 \mathrm{H}_5\right]$$
where, $k=k^{\prime}\left[\mathrm{H}_2 \mathrm{O}\right]$
e.g., (ii) inversion of cane sugar
$$\mathrm{C}_{12} \mathrm{H}_{22} \mathrm{O}_{11}+\mathrm{H}_2 \mathrm{O} \xrightarrow{\mathrm{H}^{+}} \mathrm{C}_6 \mathrm{H}_{12} \mathrm{O}_6+\mathrm{C}_6 \mathrm{H}_{12} \mathrm{O}_6$$
Rate of reaction $=k\left[\mathrm{C}_{12} \mathrm{H}_{22} \mathrm{O}_{11}\right]$
where $\quad k=k^{\prime}\left[\mathrm{H}_2 \mathrm{O}\right]$