Question

Answer the following question:
1.Define instantaneous rate of reaction.
2.Explain pseudo first-order reaction with suitable examples.

Answer 1

To solve this question, it is required to have knowledge about the rate of a reaction and its type. The rate of a reaction is the speed in which a reaction proceeds. It depends upon the concentration of the reactant, activation energy of the reaction and temperature. In some reactions, the molecularity of the reaction is different from the number of compounds affecting the rate of reaction. These reactions are known as pseudo order reactions.

Complete step by step answer:
As we know that, the rate of a reaction is dependent on the amount of reactants present in the reaction. This means that as the reaction proceeds, the amount of reactants decreases and thus the rate of reaction also decreases with time. The rate of a reaction at a particular instant of time is known as its instantaneous rate of reaction. It is a differential equation, and is dependent on the change in concentration of the reactant with respect to time.
We know that in second order reactions, the rate of reaction is dependent on the concentration of both the reactants present. In some cases, when the concentration of one of the reactants is very high, the change in its amount is practically constant with respect to the other reactant. So, the reactant is considered as a constant and the rate of reaction depends only upon one of the reactants. So, such reactions are known as pseudo first order reaction. Some examples of pseudo first order reactions are ester hydrolysis, inversion of cane sugar etc.

Note: Most of the pseudo first order reactions are the reactions involving water, i.e. then the reactant is present in a highly diluted solution. The rate constant of such reactions is only dependent on the concentration of the reactant which is present in smaller amounts.