Latent heat of a phase transition
Energy changes phase at the specified coexistence conditions.
Key knowledge
For mass m undergoing a specified equilibrium transition at fixed pressure, the latent heat magnitude is Q = mℓ. Fusion and vaporization absorb heat; their reverse transitions release it.
Values and equations
|Q_phase| = mℓ
- Q_phase
- Heat transferred for the phase change J
- m
- Transformed mass kg
- ℓ
- Specific latent enthalpy magnitude J kg⁻¹
Conditions and scope
- ℓ is specific latent enthalpy at the stated pressure and coexistence temperature; only pressure–volume work is allowed and sensible heating is accounted separately.
- The sign of heat into a system must be specified; no pressure-independent universal ℓ is assumed.
- Use a closed system with negligible changes of bulk kinetic and gravitational potential energy, and a mechanically quasistatic transition at constant pressure; no additional work modes are included.
- The heat-absorption labels for fusion and vaporization assume positive specific enthalpy change for those forward transitions. Heat-transfer direction follows the actual phase enthalpy change; the displayed magnitude alone does not determine its sign.
Sources · 4
References
Sources retain their recorded scope. A source link alone does not establish verification of every statement.
- University Physics 2: Phase ChangesSamuel J. Ling, Jeff Sanny and William Moebs / OpenStax, Rice UniversityTextbook chapter
Massachusetts Institute of Technology2 sources
- Thermal Properties of Matter · Physics (2026–27 reprint)National Council of Educational Research and Training (NCERT)Textbook chapter · PDF
Evidence and review
Fusion/vaporization heat equations and reverse-transition discussion.
Phase-change heat equals the enthalpy change for the stated stationary closed system with negligible bulk kinetic and gravitational potential energy changes and quasistatic constant-pressure work.
2026-10-10 · Independent Chemistry, Biology and Earth/Cosmos editor (AI editorial review). Source checks and independent AI editorial review of compact reference claims, equations, units, conditions and conceptual mappings. This is not human specialist certification, laboratory accreditation, whole-book verification, or a claim that all possible foundational knowledge is present.
Foundational review
2026-10-10 · Fresh primary-source inspection of the complete compact record, including every statement, equation, quantity and material condition, followed by independent AI editorial review. This check does not certify all linked lessons or every passage of every cited publication.
Sources from other places
Scope or convention differs
Ordinary equilibrium melting and vaporization use pressure-dependent latent heat with magnitude mℓ; the reverse process releases heat.
The compact school formula does not state every work-path restriction; ARK keeps the fixed-pressure, closed-system qualifications.
National Council of Educational Research and Training (NCERT)
- Thermal Properties of Matter · Physics (2026–27 reprint) IndiaEnglish
10.8 Change of state, equation10.13
- Thermal Properties of Matter · Physics (2026–27 reprint)
Entry details
Permanent link to this entry ↗- Record identity
- physics-latent-heat
- Revision
- foundations-audit.1
- Structured reference record
- University reference · University core expansion