Define melting and vaporisation

Melting is the change of a solid into a liquid at its melting point. Vaporisation is the change of a liquid into a gas, either by slow surface evaporation at any temperature or by boiling at the boiling point.

Melting in practice

• Temperature stays constant during melting while heat goes into breaking bonds.
• Latent heat of fusion is the heat needed per kilogram to melt at constant temperature.
• Examples: ice to water at 0°C, chocolate softening in a warm room.

Vaporisation in practice

• Evaporation cools the liquid because high-energy molecules escape first.
• Boiling forms bubbles in the bulk when vapor pressure equals external pressure.
• Latent heat of vaporisation is needed to separate molecules fully.