What is adsorption isotherm? Explain about Freundlich adsorption isotherm.

Explanation

(i) Adsorption isotherms represents the variation of adsorption at constant temperature. Adsorption isoterm can be studied quantitatively.
(ii) A plot between the amount of adsorbate adsorbed and pressure or concentration of adsorbate at constant temperature is called adsorption isotherms.
(iii) Freundlich adsorption isotherm.
According to Freundlich `(x)/(m)=kP^(1//n)`
Where x is the amount of adsorbate (or) adsorbed on .m. gm of adsorbent at a pressure of P. k and n are constants. Value of .n. is always less than unity.
This equation is applicable for adsorption of gases on solid surfaces. The Same equation becomes `(x)/(m)=kc^(1//n)` when used for adsorption in solutions with .c. as concentration.
(v) These equation quantitatively predict the effect of pressure (or concentration) on the adsorption of gases (or adsorbates) at constant temperature. (vi) Taking log on both sides of equation
`x/m=kP^(1//n)`
`log""(x)/(m)= log k + (1)/(n) log P`

(vii) Hence the intercept represents the value of log k and the slope ` (b)/(q) " gives " (1)/(n)`
(viii) This equation explains the increase of `(x)/(m)` with increase in pressure. But experimental values shows the deviation at low pressure.
(ix) Limitations:
(a) This equation is purely empirical and valid over a limited pressure range.
(b) The value of k and n also found vary with temperatures. No theoretical explanations were given.