Latent Heat Calculator

Latent heat of fusion (Lf) is the energy for solid↔liquid transitions (melting/freezing). Latent heat of vaporization (Lv) is for liquid↔gas transitions (boiling/condensation). Lv is always much larger than Lf because completely separating molecules into a gas requires more energy than merely disrupting the solid structure.

During a phase change, all input energy goes into breaking or forming intermolecular bonds rather than increasing molecular kinetic energy. Since temperature is a measure of average kinetic energy, it remains constant until the phase change is complete.

Steam at 100°C carries an additional 2,260 kJ/kg of latent heat compared to liquid water at 100°C. When steam contacts skin and condenses, it transfers this enormous latent heat plus the sensible heat, delivering about 7 times more energy per gram than hot water cooling from 100°C to body temperature.

Refrigerators use a refrigerant that evaporates inside the cooling coils (absorbing latent heat from the interior) and condenses outside (releasing latent heat to the room). This exploits the large latent heat of vaporization to efficiently transfer heat from cold to hot regions.

Latent heat depends on the strength of intermolecular forces. Water has an unusually high latent heat of vaporization due to extensive hydrogen bonding. Metals have varying latent heats of fusion depending on metallic bond strength. Substances with weaker intermolecular forces (noble gases, nonpolar molecules) have lower latent heats.

Water molecules form up to four hydrogen bonds each, creating an extensive 3D network. Vaporization requires breaking all these hydrogen bonds to completely separate molecules. This gives water one of the highest latent heats of vaporization (2,260 kJ/kg) among common substances.

Water vapor carries latent heat from ocean surfaces into the atmosphere. When this vapor condenses into clouds and rain, it releases enormous amounts of latent heat, warming the surrounding air and driving atmospheric circulation. Hurricanes are powered primarily by latent heat released during water vapor condensation.

Yes, you need to sum five stages: (1) heating ice to 0°C (Q=mcΔT), (2) melting ice (Q=mLf), (3) heating water from 0°C to 100°C (Q=mcΔT), (4) vaporizing water (Q=mLv), (5) heating steam above 100°C (Q=mcΔT). For 1 kg of ice at -10°C to steam at 110°C, the total is about 3,070 kJ.

Specific latent heat (L) is energy per unit mass (J/kg), while molar latent heat is energy per mole (J/mol). For water: Lv = 2,260,000 J/kg = 40,660 J/mol (dividing by molar mass 0.018 kg/mol). Molar values are preferred in chemistry; specific values in engineering.