What happenes to the temperature during a phase change?

1 Answer


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#.