Latent Heat of Vaporization Calculator

Calculator

Solve for *

Choose the unknown. Provide the other two.

Substance preset

Presets are typical reference values.

Display precision

Applies to exported files and on-page formatting.

Mass (m) *

Enter a valid mass.

Energy (Q) *

Enter a valid energy value.

Latent heat (Lv) *

Enter a valid latent heat.

Example data table

Substance	Mass (kg)	Latent heat (kJ/kg)	Energy (kJ)	Notes
Water (~100°C)	1.00	2256	2256	Typical at atmospheric pressure
Ethanol	0.50	841	420.5	Approximate at boiling point
Methanol	0.25	1100	275	Reference-style value
Ammonia	2.00	1370	2740	Common refrigeration context
Custom sample	1.20	2000	2400	Demonstrates scaling with mass

Example values are for demonstration and may vary with temperature and pressure.

Formula used

Latent heat of vaporization relates the energy needed for a phase change at constant temperature:

Energy required: Q = m × Lv
Latent heat: Lv = Q / m
Mass vaporized: m = Q / Lv

Here, Q is energy, m is mass, and Lv is latent heat per unit mass.

How to use this calculator

Select what you want to solve for (energy, mass, or latent heat).
Enter the two known quantities and choose their units.
Optionally pick a substance preset to auto-fill typical Lv.
Click Calculate to view results above the form.
Use Download CSV or Download PDF for reports.

Note: If you also heat the liquid to its boiling point, add sensible heat: Q_total = m c ΔT + m Lv.

Why latent heat of vaporization matters

Latent heat of vaporization (Lv) is the energy per unit mass needed to convert a liquid into vapor without changing temperature. It explains why boiling and evaporation can absorb large heat while the thermometer barely moves, and why phase change dominates many heat-balance problems in fluids and climate.

What this calculator computes

This tool links energy (Q), mass (m), and latent heat (Lv). Pick a mode to solve the unknown using Q = m × Lv. Outputs are shown in multiple units for quick reporting, unit checking, and side-by-side comparison across different reference systems. This reduces conversion errors and speeds documentation work.

Units and conversions included

Enter energy in J, kJ, MJ, cal, kcal, or BTU, and mass in g, kg, lb, or metric ton. Lv supports J/kg, kJ/kg, J/g, cal/g, kcal/kg, and BTU/lb. The calculator converts to base units internally before computing.

Typical latent heat values

Lv depends on the substance and conditions. Near normal boiling points, water is about 2256 kJ/kg, ethanol about 841 kJ/kg, methanol about 1100 kJ/kg, ammonia about 1370 kJ/kg, and benzene about 394 kJ/kg. Use these as reality checks when you test inputs.

Temperature and pressure dependence

Lv generally decreases as temperature rises and approaches zero at the critical point. Pressure changes the boiling point, so the effective Lv for a process can shift in vacuum systems or pressurized vessels. For high accuracy, use property tables at your operating state.

Sensible plus latent energy

If the liquid must be warmed to the phase-change temperature, combine sensible and latent terms: Q_total = m c ΔT + m Lv. For small ΔT, the latent term usually dominates; for large ΔT, both can be important, especially for high-heat-capacity liquids.

Where the calculation is used

Lv appears in distillation, steam generation, refrigeration, humidification, and drying. In atmospheric science, evaporation and condensation redistribute heat and influence humidity and cloud development. In food processing and chemical plants, Lv-based estimates help plan energy consumption, heating time, and equipment loads.

Practical tips for clean inputs

Confirm the chosen mode, use consistent units, and apply a preset only when its reference conditions match your problem. If your process is far from the normal boiling point, look up Lv at the relevant temperature and pressure. Finally, compare results to typical values for sanity.

FAQs

1) What is the difference between evaporation and boiling?

Evaporation occurs at the surface at any temperature, while boiling occurs throughout the liquid when vapor pressure matches ambient pressure. Both require latent energy, but boiling is strongly tied to the boiling point.

2) Does latent heat change with temperature?

Yes. For most liquids, Lv decreases as temperature increases and trends toward zero near the critical point. For accurate work, use Lv values tabulated at your operating temperature and pressure.

3) Can I use this calculator for condensation?

Yes. Condensation releases approximately the same magnitude of energy as vaporization absorbs. Use the same Lv, but interpret Q as energy released instead of required input energy.

4) Why do my results look too large?

Check units first. A common mistake is mixing grams with kJ/kg or using kcal where kJ was intended. Convert mass and Lv consistently, or select matching units in the form before calculating.

5) Should I include heating the liquid to boiling?

If the liquid starts below the phase-change temperature, include sensible heating: m c ΔT. This calculator focuses on the phase-change term, so add sensible heat separately when needed.

6) What Lv value should I use for water?

At 100°C and 1 atm, water is commonly approximated as 2256 kJ/kg. At lower temperatures, the value is higher. Use a steam table if your process is not near 100°C.

7) How precise are the preset substance values?

Presets are representative reference values near normal boiling points, suitable for estimates and education. For design or lab-grade accuracy, replace the preset with a property value at your exact temperature and pressure.