Evaporation vs Boiling

Quick Answer

Evaporation happens at the surface at any temperature. Boiling happens throughout the liquid at a specific temperature.

What Each One Really Means

Many people use these words as if they mean the same thing. They do not. The difference is where the change is happening and at what temperature. Evaporation happens only at the surface of a liquid. The fastest particles escape into the air, and this can happen at any temperature. That is why a puddle of water disappears on a hot afternoon and also why wet clothes dry slowly in a cold room. There is no fixed temperature for evaporation. Boiling is different. It happens throughout the entire volume of the liquid, not just the surface. Bubbles form inside the liquid, rise, and burst at the top. But boiling only happens when the vapour pressure of the liquid equals the atmospheric pressure outside. That is why water boils at 100 degrees Celsius at sea level but at a lower temperature on a mountain. Lower atmospheric pressure, lower boiling point. This is also why cooking takes longer at high altitude. The water boils, but at a lower temperature, so the food cooks slower. I always tell my students that evaporation is quiet and slow. Boiling is loud and fast. One happens at any temperature, the other only happens at one specific temperature for a given pressure. If you mix them up in an exam, you will lose marks on kinetic theory questions, because the underlying mechanisms are different.

Side-by-Side Comparison

Memory Device

Evaporation is 'e-vapour-ation'. Vapour just leaves. Boiling is war on all fronts.

Related Topics