Intermediate Topic 265 of 1102 States of Matter & Solutions
Enthalpy of Fusion
Heat required to melt one mole of solid at its melting point.
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In-depth explanation of Enthalpy of Fusion
The enthalpy of fusion is the heat energy needed to melt one mole of a solid at its melting point, with the temperature remaining constant during melting. The energy goes into weakening the ordered arrangement of particles rather than into raising their kinetic energy. Its value is smaller than the enthalpy of vaporization because the particles in a liquid are still close together, so less energy is needed than to separate them into a gas. Enthalpy of fusion is used in heat packs and in calculating the energy needed to melt ice. Freezing releases the same amount of energy in the reverse direction.
Going deeper: Enthalpy of Fusion
Key ideas: Use q = n ΔHfus for melting; the energy is released in freezing. Ice: 6.01 kJ/mol or 334 J/g. Typical ordering is ΔHfus much smaller than ΔHvap, with the ratio often around 1 to 5 to 1 to 10. Trouton-like estimates also exist for entropy of fusion.
Common mistakes and connections: Students often forget to include the fusion step in heating calculations, or confuse specific heat with latent heat. For ice at -10 C to water at 20 C, three terms are needed: warming ice, melting, warming water. Temperature stays constant during the phase change. Links to heating curves, calorimetry and the freezing point depression of solutions.
Visualization of Enthalpy of Fusion
Hfus is the heat to melt one mole at its melting point; it is much smaller than Hvap because melting only loosens the lattice. The interactive lesson shows this as a live animation or chart.
Worked example and use case
Melting one mole of ice at 0°C requires 6.01 kJ, which is why ice absorbs heat from a drink while melting without raising the temperature of the ice.
Frequently asked questions about Enthalpy of Fusion
What is Enthalpy of Fusion?
Heat required to melt one mole of solid at its melting point.
Is Enthalpy of Fusion a beginner, intermediate or advanced topic?
Enthalpy of Fusion is a intermediate topic in States of Matter & Solutions. It builds on the vocabulary of beginner topics in this area.
What should I learn before Enthalpy of Fusion?
Study these earlier topics in States of Matter & Solutions first: Cohesion and Adhesion, Meniscus, Enthalpy of Vaporization.
What comes after Enthalpy of Fusion?
The next topics in States of Matter & Solutions are Heating Curve and Sublimation.
Can I practise Enthalpy of Fusion with quizzes?
Yes. The interactive lesson includes a self-check question on Enthalpy of Fusion, and the States of Matter & Solutions quiz draws on every topic in this area.
Where Enthalpy of Fusion fits in States of Matter & Solutions
Enthalpy of Fusion is topic 46 of 109 in States of Matter & Solutions.