Latent Heat
Calculate latent heat energy absorbed or released during phase transitions (melting, freezing, boiling, condensation) using Q = mL. Free online thermodynamics calculator with substance presets and charts.
About This Calculator
The Latent Heat Calculator computes the heat energy absorbed or released during phase transitions of substances using the fundamental thermodynamics formula Q = m × L. This tool is essential for physics and chemistry students, HVAC and thermal engineers, and anyone studying thermodynamics or working with phase change materials.
The calculator includes preset specific latent heat values for common substances including water (fusion: 334 kJ/kg, vaporization: 2260 kJ/kg), ethyl alcohol, ammonia, copper, iron, aluminum, gold, and many more substances covering both solid-liquid and liquid-gas transitions. You can also enter a custom specific latent heat value for any substance not in the preset list. The formula Q = mL gives the latent heat in joules, where energy is absorbed during melting and boiling (endothermic) and released during freezing and condensation (exothermic).
What is Latent Heat?
Latent heat (from Latin latere meaning "to lie hidden") is the hidden heat energy absorbed or released during a phase change without a change in temperature. When ice melts at 0°C, it absorbs 334 kJ of energy per kilogram to break the crystalline structure — the temperature stays at 0°C until all ice has melted. Similarly, water at 100°C requires 2260 kJ per kilogram to become steam, which is why steam burns are so dangerous (they carry enormous latent heat energy). The reverse process releases the same amount of energy — steam condensing on your skin releases that 2260 kJ/kg directly. This concept is fundamental to understanding weather (evaporation and condensation drive storms), refrigeration cycles, power generation, and countless industrial processes.
Regional Notes
Global (SI units): This calculator uses SI units — mass in kilograms (kg), specific latent heat in J/kg, and results in joules (J) and kilojoules (kJ).
United States: In imperial units, latent heat can be expressed in BTU/lb. Water's latent heat of vaporization is approximately 970 BTU/lb at 212°F. To convert kilojoules to BTU, multiply by 0.9478.
United Kingdom: UK users typically work in SI units (kg, kJ) consistent with this calculator. The construction and HVAC industries may also see latent heat referenced in kW for heating/cooling power ratings.
Frequently Asked Questions
What is latent heat?
Latent heat is the heat energy absorbed or released by a substance during a phase transition (solid to liquid, liquid to gas, or vice versa) without changing its temperature. The energy goes into breaking or forming intermolecular bonds rather than raising the temperature.
How do you calculate latent heat?
Latent heat is calculated using the formula Q = m × L, where Q is the latent heat energy in joules (J), m is the mass of the substance in kilograms (kg), and L is the specific latent heat in J/kg. For water melting at 0°C, Q = mass × 334,000 J/kg.
What is the difference between latent heat of fusion and vaporization?
Latent heat of fusion is the energy required to change a substance from solid to liquid (melting) or released when changing from liquid to solid (freezing). Latent heat of vaporization is the energy required to change from liquid to gas (boiling/evaporation) or released when changing from gas to liquid (condensation). Vaporization typically requires much more energy than fusion.
What is the specific latent heat of water?
Water has a specific latent heat of fusion of 334,000 J/kg (334 kJ/kg) and a specific latent heat of vaporization of 2,260,000 J/kg (2,260 kJ/kg). This means turning 1 kg of ice at 0°C into water requires 334 kJ, and turning 1 kg of water at 100°C into steam requires 2,260 kJ of energy.
What is the difference between specific latent heat and specific heat capacity?
Specific latent heat is the energy per kilogram absorbed or released during a phase change at constant temperature, while specific heat capacity is the energy per kilogram per degree Celsius required to change the temperature of a substance without changing its phase. They describe different physical processes.
What units are used for latent heat?
Latent heat is measured in joules (J) or kilojoules (kJ) in SI units. Specific latent heat is measured in J/kg or kJ/kg. This calculator provides results in both joules and kilojoules for your convenience.
Can latent heat be negative?
Yes, latent heat can be considered negative when heat is released from the substance during exothermic phase changes like freezing (liquid to solid) or condensation (gas to liquid). The magnitude remains the same, but the energy flows out of the substance rather than into it.
How is latent heat used in real-world applications?
Latent heat is essential in refrigeration and air conditioning (evaporation and condensation cycles), steam power plants, sweat evaporative cooling, thermal energy storage using phase change materials, food preservation through freezing, and meteorological phenomena like cloud formation and precipitation.