What does change of state mean?

1 Answer


Solid #harr# Liquid #harr# Gas


Change of state deals with the change from one (state of matter) to another in the form of Solid #harr# Liquid #harr# Gas.

Every element/compound/material has different temperatures that affect the state of the matter:

  • melting/freezing point to go from [solid to liquid]/[liquid to solid]
  • boiling point to go between liquid and gas.

To melt a solid is to supply heat into the system (i.e. in an endothermic process), breaking the ionic interactions in the crystal lattice structure and replacing them with weaker intermolecular forces that are present in a liquid.

Freezing a liquid does the opposite, releasing energy in an exothermic fashion.

Boiling requires supplying energy to break the intermolecular forces in a liquid and allowing the particles to move freely as a gas. Therefore, it is an endothermic process.

Condensation releases energy to transition from the gas to liquid phase and is the exact opposite. That is, it is exothermic.

Bonus: there are some materials that can go directly from Solid #harr# Gas through what is known as sublimation