Cohesion is attraction between like molecules; adhesion is attraction to other substances.
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Cohesion is the attraction between molecules of the same substance, which holds a liquid together, while adhesion is the attraction between molecules of a liquid and a different substance, such as a container wall. Both are intermolecular forces, and the balance between them determines how a liquid wets a surface. If adhesion is greater than cohesion the liquid spreads over and wets the surface, and if cohesion is greater it beads up. These effects control the shape of the meniscus, the spreading of paint and the action of detergents. Water shows strong cohesion because of hydrogen bonding, and it adheres well to clean glass.
Key ideas: Compare the forces to predict wetting: contact angle below 90 degrees means adhesion wins and the liquid wets, above 90 means cohesion dominates. Water wets clean glass but beads up on wax. Cohesion explains surface tension and also the high tensile strength of water in tall trees.
Common mistakes and connections: A common confusion is thinking cohesion and adhesion are the same force acting between the same species. Another is believing wettability is a property of the liquid alone, when it depends on the pair of liquid and surface. Linked to meniscus shape, capillary action, surfactants and adhesives.
Water adhesion to glass exceeds its cohesion so it climbs walls; mercury has stronger cohesion, so it bulges and forms a convex meniscus. The interactive lesson shows this as a live animation or chart.
Water forms a concave meniscus in a glass tube because its adhesion to glass is stronger than its cohesion.
Cohesion is attraction between like molecules; adhesion is attraction to other substances.
Cohesion and Adhesion is a beginner topic in States of Matter & Solutions. It needs no earlier chemistry lessons and is a good starting point.
Study these earlier topics in States of Matter & Solutions first: Viscosity, Surface Tension, Capillary Action.
The next topics in States of Matter & Solutions are Meniscus and Enthalpy of Vaporization.
Yes. The interactive lesson includes a self-check question on Cohesion and Adhesion, and the States of Matter & Solutions quiz draws on every topic in this area.
Cohesion and Adhesion is topic 43 of 109 in States of Matter & Solutions.