10.4 Change in State
By absorbing or losing energy, the kinetic energy of the atoms or molecules of a substance changes, which can lead to a change in the state of matter. Change in state occurs when matter loses or absorbs energy.
When a substance absorbs energy, the atoms and molecules move more rapidly and need more space and separation. This may lead to a solid turning into a liquid, called melting, and a liquid turning into a gas, called boiling.
By losing energy, the atoms and molecules slow down and there is less space and separation between them. This may lead to a gas turning into a liquid, called condensation, and a liquid turning into a solid, called solidification.
Intermolecular forces are strongest in solids due to the least separation and weakest in gases, as the molecules are far apart compared to liquids and solids. This is the reason that gases exhibit the greatest relative thermal expansion, while solids have the least expansion.