What happenes to the temperature during a phase change?

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1 Answer
SCooke · Truong-Son N.
Dec 13, 2016

The compound temperature remains constant, the surrounding temperature changes.

Explanation:

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.
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