Long Answer TypeThe variation in the amount of gas adsorbed by the adsorbent with pressure at constant temperature can be expressed by means of a curve termed as adsorption isotherm.
Most of the adsorptions are exothermic reactions, Hence adsorption generally depends on temperature. Exothermic reactions are mostly spontaneous at low temperature. Hence the extent of adsorption decreases with the increase of temperature at constant pressure. A plot of the extent of adsorption versus temperature at constant pressure is known as adsorption Isobar.
Freundlich adsorption isotherm: Freundlich gave an empirical relationship between the quantity of gas adsorbed by a unit mass of solid adsorbent and pressure at a particular temperature. The
the relationship can be expressed by the following equation:
Freundlich Isotherm: The relationship between x/m and pressure of the gas at constant temperature is called adsorption isotherm and given as by 
and n depend upon the nature of gas and the solid.
x/m first increase with the increase in pressure at low pressure but becomes independent of pressure at high pressure.
Thus three cases arise from the graph
At low pressure, the extent of adsorption is directly proportional to pressure (raised to power one).
At high pressure, the extent of adsorption is independent of pressure (raised to power zero).
Therefore at an intermediate value of pressure, adsorption is directly proportional to pressure raised to power 1/n.Here n is a variable whose value is greater than one.
Using constant of proportionality, k, also known as adsorption constant we get
The above equation is known as Freundlich adsorption equation.
As per Freundlich adsorption equation
Taking logarithm on both sides, we get
Here x is the weight of the gas absorbed by m mass of the adsorbent at a pressure p, k and n are constant (at a particular temperature) and for a particular adsorbate-adsorbent pair.
The equation above equation is comparable with comparable with the equation of a straight line,
y = m x + c where m represents the slope of the line and c represents intercept on y-axis.
Plotting a graph between log(x/m) and log p, we will get a straight line with the value of slope equal to 1/n and log k as y-axis intercept.
log(x/m) vs. log p graph.
(i) Explain the meaning of the statement. ‘Adsorption is a surface phenomenon.’
(ii) State two features of chemical adsorption which are not found in physical adsorption.
(iii) Explain the terms with suitable examples: (i) Gel, (ii) Aerosol and (iii) Hydrosol.
Short Answer TypeOut of BaCl2 and KCl, which one is more effective in causing coagulation of a negatively charged colloidal Sol? Give reason.
In reference to Freundlich adsorption isotherm, write the expression for adsorption of gases on solids in the form of an equation.
Based on the type of particles of dispersed phase, give one example each of associated colloid and multimolecular colloid.
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