Advanced Topic 321 of 1102 States of Matter & Solutions
Freundlich Isotherm
An empirical relation between amount adsorbed and pressure.
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In-depth explanation of Freundlich Isotherm
The Freundlich isotherm is an empirical equation describing how the amount of gas or solute adsorbed per unit mass of adsorbent depends on the equilibrium pressure or concentration. It is written x/m = k P^(1/n), where x/m is the amount adsorbed per gram, P is the pressure, and k and n are constants that depend on the adsorbate, the adsorbent and the temperature. Taking logarithms gives a straight line with slope 1/n and intercept log k. The isotherm fits experimental data well at moderate pressures but is not a physical model of surface coverage. It is widely used for adsorption on activated charcoal and in water treatment.
Going deeper: Freundlich Isotherm
Key ideas: Linear form: log(x/m) = log k + (1/n) log P, with 1/n between 0 and 1. A plot of log(x/m) against log P gives a slope of 1/n and intercept log k. At low pressure the dependence is nearly linear; at high pressure it approaches independence from pressure when 1/n tends to 0. For solutions, replace P with concentration C.
Common mistakes and connections: Students use the equation without logs or misread slope and intercept. Another error is extrapolating it to very high pressure, where adsorption saturates but the equation keeps increasing. Constants vary with temperature and are not universal. Links to Langmuir isotherm, adsorption on charcoal and water treatment design.
Visualization of Freundlich Isotherm
Freundlich isotherm x/m = k P^(1/n): adsorbed amount rises with pressure but increasingly slowly, with no saturation limit. The interactive lesson shows this as a live animation or chart.
Worked example and use case
Adsorption of a gas on charcoal fits the Freundlich equation well at moderate pressures, giving a straight line on a log-log plot.
Frequently asked questions about Freundlich Isotherm
What is Freundlich Isotherm?
An empirical relation between amount adsorbed and pressure.
Is Freundlich Isotherm a beginner, intermediate or advanced topic?
Freundlich Isotherm is a advanced topic in States of Matter & Solutions. It builds on beginner and intermediate topics, so review those first if needed.
What should I learn before Freundlich Isotherm?
Study these earlier topics in States of Matter & Solutions first: Micelles, Gels and Sols, Adsorption.
What comes after Freundlich Isotherm?
The next topics in States of Matter & Solutions are Langmuir Isotherm and Coagulation.
Can I practise Freundlich Isotherm with quizzes?
Yes. The interactive lesson includes a self-check question on Freundlich Isotherm, and the States of Matter & Solutions quiz draws on every topic in this area.
Where Freundlich Isotherm fits in States of Matter & Solutions
Freundlich Isotherm is topic 102 of 109 in States of Matter & Solutions.