During a phase change, the temperature of a substance remains constant because the added heat energy is used to break or form intermolecular forces, not to increase the kinetic energy of the molecules. This means the heat is absorbed or released as latent heat, which is the energy required for a substance to change its state without a temperature change.
Here’s a more detailed explanation:
Intermolecular Forces:
Substances in different states (solid, liquid, gas) have different intermolecular forces. For example, solids have strong intermolecular forces holding them together, while gases have weak forces.
Latent Heat:
When a substance changes state, the heat absorbed or released is used to overcome these intermolecular forces, not to raise the temperature. This heat is called latent heat.
No Temperature Rise:
During a phase change, the temperature remains constant because the added heat is being used to break or create intermolecular bonds, not to increase the average kinetic energy of the molecules (which is what determines temperature).