Advanced Topic 320 of 1102 States of Matter & Solutions
Adsorption
Accumulation of molecules on a surface, important in catalysis and purification.
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In-depth explanation of Adsorption
Adsorption is the accumulation of molecules, atoms or ions at the surface of a solid or liquid, forming a thin layer distinct from the bulk phase. Physical adsorption, or physisorption, involves weak van der Waals forces and is reversible, whereas chemical adsorption, or chemisorption, forms chemical bonds and is often irreversible. The extent of adsorption increases with the surface area of the adsorbent and with pressure or concentration, and it generally decreases with temperature. Adsorption is important in catalysis, gas masks, water purification and chromatography. Activated charcoal has a very large surface area, which makes it an excellent adsorbent.
Going deeper: Adsorption
Key ideas: Compare: physisorption has enthalpy of about 20 to 40 kJ/mol, multilayer, fast, reversible, lowers with temperature; chemisorption has 80 to 240 kJ/mol, monolayer, may need activation energy, specific. Adsorption is exothermic and has negative entropy change, so it is favourable at lower temperature. Units for amount: per gram of adsorbent.
Common mistakes and connections: Students confuse adsorption with absorption; absorption takes the substance into the bulk, like a sponge. Another error is thinking increase in temperature always helps; physisorption decreases. Catalyst poisons are strongly chemisorbed. Links to Freundlich and Langmuir isotherms, catalysis, chromatography and surface area.
Visualization of Adsorption
Physisorption decreases as temperature rises, while chemisorption first increases (activation needed) and then decreases. The interactive lesson shows this as a live animation or chart.
Worked example and use case
Activated charcoal adsorbs odour molecules from the air, which is why it is used in water filters and air purifiers.
Frequently asked questions about Adsorption
What is Adsorption?
Accumulation of molecules on a surface, important in catalysis and purification.
Is Adsorption a beginner, intermediate or advanced topic?
Adsorption 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 Adsorption?
Study these earlier topics in States of Matter & Solutions first: Emulsions, Micelles, Gels and Sols.
What comes after Adsorption?
The next topics in States of Matter & Solutions are Freundlich Isotherm and Langmuir Isotherm.
Can I practise Adsorption with quizzes?
Yes. The interactive lesson includes a self-check question on Adsorption, and the States of Matter & Solutions quiz draws on every topic in this area.
Where Adsorption fits in States of Matter & Solutions
Adsorption is topic 101 of 109 in States of Matter & Solutions.