Surface Chemistry MCQ Questions & Answers in Physical Chemistry | Chemistry

When a gas is adsorbed on the surface, the freedom of movement of its molecules becomes restricted. This causes decrease in the entropy of the gas after adsorbtion, i.e. $$\Delta S$$  becomes negative.

No. of sodium lauryl sulphate molecules $$\left( {C{H_3}{{\left( {C{H_2}} \right)}_{11}}SO_4^ - N{a^ + }} \right)$$     in 1 litre solution $$ = {10^{ - 3}} \times 6 \times {10^{23}} = 6 \times {10^{20}}$$
No. of sodium lauryle sulphate molecules per $$m{m^3} = 6 \times {10^{14}}$$
No. of colloidal particles per $$m{m^3} = {10^{13}}$$
No. of molecules per colloidal particle $$ = \frac{{6 \times {{10}^{14}}}}{{{{10}^{13}}}} = 60$$

As adsorption is an exothermic process.
∴ Rise in temperature will decrease adsorption ( according to Le-chatelier principle ) .

If we plot a graph between $${\text{log}}\left( {\frac{x}{m}} \right)$$  and $${\text{log}}\,p,$$  a straight line will be obtained. The slope of the line is equal to $$\frac{1}{n}$$  and the intercept is equal to $${\text{log}}\,k.$$

where, $$\frac{x}{m} = $$  amount of adsorption
According to Freundlich adsorption isotherm
$$\eqalign{ & \frac{x}{m} = k{p^{\frac{1}{n}}} \cr & {\text{Taking log of both sides,}} \cr & {\text{log}}\,\frac{x}{m} = {\text{log}}\,k + \frac{1}{n}\,{\text{log}}\,p \cr & {\text{from}}\,\,y = zx + c \cr & \,\,\,\,\,\,\,\,\,\,\,\,\,z = \frac{1}{n}\left( {{\text{slope}}} \right) \cr} $$

In aerosol, the dispersion medium is gas while the dispersed phase can be both solid or liquid.

The adsorption of methylene blue on activated charcoal is an example of physiosorption which is exothermic, multilayer and does not have energy barrier.

Low temperature is favourable for physisorption. It increases with decrease of temperature.

Butter is an example of water in oil type emulsion.

Thixotropic gel changes into sol on mechanical agitation, which on standing sets to gel.

$$n$$  is always greater than one.