Cambridge IGCSE Chemistry · Syllabus 0620 · States of Matter
Change of state
What is Change of state?
A physical change in which a substance goes from one state of matter to another - solid, liquid or gas - because energy is transferred to or from it. The five changes of state named by the syllabus are melting (solid to liquid), boiling and evaporating (liquid to gas), condensing (gas to liquid) and freezing (liquid to solid). Melting, boiling and evaporating require energy to be transferred to the substance; condensing and freezing require energy to be transferred away from it. The substance itself is unchanged: no new substance is made, the particles keep their size and chemical identity, and the change can be reversed by reversing the energy transfer.
This definition is part of the States of Matter chapter in Cambridge IGCSE Chemistry.
Examiner tips on Change of state
- The single most valuable sentence in this route: a change of state overcomes the attractive forces between particles. It does not break the covalent bonds inside a molecule. Steam is still \(\mathrm{H_2O}\); ice is still \(\mathrm{H_2O}\). Nothing chemical has happened.