What happens to temperature during a phase change?

During a phase change, the temperature of a substance remains constant despite the continuous addition or removal of heat. This occurs because the energy supplied or extracted during a phase change is used to alter the intermolecular forces rather than to increase or decrease the kinetic energy of the molecules, which is what affects temperature.

For example, when ice is melting to become water, the heat energy provided goes into breaking the hydrogen bonds between water molecules. During this process, the temperature of the ice-water mixture stays at 0°C until the entire ice has melted. Similarly, during the phase transition from liquid to gas (like boiling), the temperature remains constant at the boiling point until the entire liquid phase has transformed into gas. The constant temperature during these transitions is a key concept in thermodynamics and helps explain why certain temperature readings do not change during state transitions.

Understanding this principle is crucial in various scientific fields, from chemistry to environmental science, as it describes how energy is distributed in physical processes involving matter.