Graph illustrating the heating process of a substance, including temperature increases and a plateau during phase change.

- The graph shows a heating curve for a substance, indicating temperature changes over time as heat is added.
- Segment AB represents the heating of the solid phase; temperature increases as heat is absorbed.
- Segment BC is a plateau where temperature remains constant; this is the melting point, and the substance is undergoing a phase change from solid to liquid (latent heat of fusion).
- Segment CD shows the heating of the liquid phase; temperature rises again as more heat is absorbed.
- Segment DE is another plateau at a higher temperature; this is the boiling point, and the substance is changing from liquid to gas (latent heat of vaporization).
- Segment EF represents the heating of the gaseous phase; temperature continues to increase with added heat.
- The flat segments (BC and DE) indicate phase changes where energy is used to break intermolecular bonds rather than raise temperature.