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Karnataka Board PUCPUC Science 2nd PUC Class 12

Adsorption Isotherms (Freundlich and Langmuir Adsorption Isotherm)

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Estimated time: 6 minutes
Maharashtra State Board: Class 12

Definition: Adsorption Isotherm

The relationship between the extent of adsorption (x/m) and the pressure of gas at constant temperature is called an adsorption isotherm.

Maharashtra State Board: Class 12

Key Points: Adsorption Isotherm

Freundlich Adsorption Isotherm:

Empirical equation: \[\frac{x}{m}=kP^{1/n}\quad(n>1)\]

where:

  • x = mass of the gas adsorbed
  • m = mass of the adsorbent
  • `x/m` = mass of gas adsorbed per unit mass of adsorbent
  • P = equilibrium pressure
  • k and n = constants depending on the nature of the adsorbate, adsorbent, and temperature

For solutions: \[\frac{x}{m}=kC^{1/n}\] where C = concentration of the solution

Logarithmic (linear) form: \[\log\frac{x}{m}=\log k+\frac{1}{n}\log P\]

In the log x/m vs log P graph:

  • Slope = `1/n` (value between 0 and 1)
  • Y-intercept = log k
  • When `1/n` = 0: adsorption is independent of pressure
  • When `1/n` = 1: adsorption is directly proportional to pressure

Shaalaa.com | Surface Chemistry part 7 (Adsorption Isotherms)

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Surface Chemistry part 7 (Adsorption Isotherms) [00:09:23]
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