The temperature remains constant during the change of state for any substance because the heat energy supplied is used entirely to overcome the intermolecular forces or attractive forces between the particles rather than increasing their kinetic energy. This heat energy used for the phase change is called latent heat. Since the energy goes into changing the state (e.g., melting, boiling) and not into increasing the molecular motion, the temperature does not change until the entire substance has completed the transition to the new phase. Only after the phase change is complete can the temperature start to rise or fall again with heat addition or removal.
Explanation
- During heating, when a substance reaches its melting or boiling point, the temperature stabilizes.
- All the heat energy supplied at this stage is consumed in breaking the intermolecular bonds, which changes the state of the substance.
- Since temperature corresponds to the average kinetic energy of molecules, and this energy doesn't increase during phase change, temperature remains constant.
- This phenomenon happens in both melting/freezing and boiling/condensation processes.
Concept of Latent Heat
- The latent heat is the amount of heat absorbed or released by the substance during the phase change without a change in temperature.
- It represents the hidden energy that facilitates the rearrangement of particles, allowing the conversion from one state to another.
In summary, temperature remains constant during a change of state because the heat energy is used for breaking or forming intermolecular attractions rather than increasing molecular kinetic energy, which would raise the temperature.
