Question

At equilibrium, the rate of dissolution of a solid solute in a volatile liquid is:
A. Less than the rate of crystallisation
B. Greater than the rate of crystallisation
C. Equal to the rate of crystallisation
D. Zero

Answer 1

Hint: At equilibrium the rate of the forward reaction is equal to the rate of the backward reaction. The concentration of reactant is also equal to the concentration of products at equilibrium. We will consider the forward reaction to be dissolution and the backward reaction will be crystallisation.

Complete solution:
Equilibrium is the state of a reaction at which the reaction seems as if it has stopped but in reality the velocity of the forward reaction is equal to the velocity of the backward reaction. This can also be expressed in terms of the concentration of the reactants. As mentioned in the hint, we know that at equilibrium the mass of the reactants is the same as the mass of the products. The reaction mentioned in the question is a process where a solid solute is dissolved in a liquid solvent. This process is called a dissolution.
The rate of dissolution can change depending on the amount of solute to be dissolved. For example, if some solute is already dissolved in the solvent and it has the capability of allowing more solute to dissolve in it then we call it an undersaturated solution. A saturated solution is a solution where the maximum amount of solute can be dissolved at that particular temperature. If we increase the temperature of the solvent, we can add more solute and it will dissolve. This is an oversaturated solution.
At equilibrium, we can say that the rate of dissolution can be considered as the forward reaction and the rate of crystallisation will be the backward reaction. This means that the rate of crystallisation is equal to the rate of the dissolution for a solid solute in a volatile liquid.

This means that the answer to the above question will be option C.

Note: At equilibrium the rate of dissolution will be equal to the rate of crystallisation.
On increasing the temperature of a solute, there is an increase in the solubility of a solute in the solvent. This can lead to the formation of a highly saturated solution.