What happenes to the temperature during a phase change?
The compound temperature remains constant, the surrounding temperature changes.
Phase changes go both ways, so the thermal energy of the system may increase or decrease.
DURING a phase change, the temperature of the compound remains constant as the thermal energy is absorbed or released, where the magnitude is according to its unique heats of vaporization or fusion.
- Freezing (heat of fusion,
#DeltaH_"fus"#) and condensation are exothermic (heat of vaporization, #DeltaH_"vap"#), since they involve slowing down molecular motion, and thus energy is released and #DeltaH < 0#.
- Melting (heat of fusion,
#DeltaH_"fus"#) and vaporization (heat of vaporization, #DeltaH_"vap"#) are endothermic, since they involve speeding up molecular motion, and thus energy is absorbed and #DeltaH > 0#.