Question

The correct statement(s) about surface properties is/are:

• A. The critical temperatures of ethane and nitrogen are $563K$ and $126K$ respectively. The adsorption of ethane will be more than that of nitrogen of same amount of activated charcoal at a given temperature
• B. Cloud is an emulsion type of colloid in which liquid is dispersed phase and gas is dispersion medium
• C. Adsorption is accompanied by decrease in enthalpy and decrease in entropy of the system
• D. Brownian motion of collodial particles does not depend on the size of the particles but depends on viscosity of the solution

Answer 1

Answer: (A), (C)

Adsorption is accompanied by decrease in enthalpy and decrease in entropy of the system

(a) Higher the critical temperature, higher will be extent of adsorption. As critical temperature of ethane is more than nitrogen, adsorption of ethane will be more than nitrogen.

(b) Cloud is an aerosol, emulsions are liquid-liquid collodial system.

(c) During adsorption, there is always a decrease in residual forces of the surface, i.e., there is decrease in surface energy which appears as heat. Adsorption, therefore, is invariably an exothermic process. In other words, $\Delta H$ of adsorption is always negative. When a gas is adsorbed, the freedom of movement of its molecules become restricted. This amounts to decrease in the entropy of the gas after adsorption, i.e., $\Delta S$ is negative.

(d) Brownian movement of collodial particals depends on size of particles.