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Energy of Phase Changes

Phase changes involve the transformation of a substance from one state of matter to another, accompanied by energy absorption or release.

Key Concepts​

  • Endothermic Phase Changes: Energy is absorbed from the surroundings
    • Examples: Melting (solid → liquid), Vaporization (liquid → gas), Sublimation (solid → gas)
  • Exothermic Phase Changes: Energy is released to the surroundings
    • Examples: Freezing (liquid → solid), Condensation (gas → liquid), Deposition (gas → solid)

Energy Considerations​

  • Heat of Fusion (ΔH_fus): Energy required to melt 1 mole of a solid
  • Heat of Vaporization (ΔH_vap): Energy required to vaporize 1 mole of a liquid
  • Calorimetry Equations: q = m × ΔH for phase changes (no temperature change occurs)

Importance​

  • Helps understand energy flow during phase changes
  • Critical for thermodynamics, material science, and chemical engineering
  • Essential in industrial processes, heating/cooling, and everyday phenomena

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