5.7 understand the changes that occur when a solid melts to form a liquid, and when a liquid evaporates or boils to form a gas

Solid à Liquid

In a solid the particles are tightly packed in a regular pattern. As heat is applied it is transferred to kinetic energy as the particles gain kinetic energy. When they have enough kinetic energy they break free from the intermolecular forces holding them together as a solid and become a liquid.

Liquid à Gas

In a liquid the particles are free and are in an irregular pattern. As more heat is applied the particles gain more kinetic energy until they have enough kinetic energy to overcome the intermolecular forces holding them together. They now have little or no intermolecular force and are a gas.