Latent Heat Calculator
Free calculate energy required for phase changes (fusion, vaporization) using q = ml. Get instant, accurate results with our easy-to-use calculator.
Input Parameters
Results
Enter values to calculate
What is Latent Heat?
Latent heat is the energy required to change the phase of a substance (solid to liquid, liquid to gas) without changing its temperature. It's "hidden" because it doesn't cause a temperature change.
There are two main types: latent heat of fusion (melting/freezing) and latent heat of vaporization (boiling/condensation). Vaporization typically requires much more energy than fusion.
Latent heat explains why ice at 0°C requires energy to melt, why sweating cools you (evaporation absorbs heat), and why phase changes occur at constant temperature. It's fundamental in thermodynamics and heat transfer.
Latent Heat Formula
Where:
- • Q = Heat energy (J)
- • m = Mass (kg)
- • L = Latent heat (J/kg)
Types:
- • L_f = Latent heat of fusion (melting)
- • L_v = Latent heat of vaporization (boiling)
How to Calculate Latent Heat
-
1
Identify the phase change
Determine if you're calculating fusion (melting) or vaporization (boiling) energy.
-
2
Find the latent heat value
Look up the specific latent heat (L_f or L_v) for your substance. Water: L_f = 334 kJ/kg, L_v = 2256 kJ/kg.
-
3
Convert mass to kilograms
Ensure mass is in kg for consistent units with J/kg.
-
4
Apply the formula
Calculate Q = m × L
Practical Examples
Example 1: Melting Ice
How much energy is needed to melt 2 kg of ice at 0°C? (L_f = 334 kJ/kg)
Solution:
Q = m × L_f = 2 kg × 334 kJ/kg
Q = 668 kJ = 668,000 J
Example 2: Boiling Water
How much energy is needed to vaporize 1 kg of water at 100°C? (L_v = 2256 kJ/kg)
Solution:
Q = m × L_v = 1 kg × 2256 kJ/kg
Q = 2256 kJ (much more than melting!)
Applications
Refrigeration
Understanding how refrigerants absorb heat during phase changes to cool spaces efficiently.
Weather
Explaining how evaporation cools surfaces, why condensation releases heat, and cloud formation processes.
Manufacturing
Metal casting, welding, and processes requiring precise control of phase changes and energy input.
Chemistry
Understanding phase diagrams, distillation, and separation processes based on different boiling points.
Frequently Asked Questions
Why doesn't temperature change during phase change?
All energy goes into breaking molecular bonds (solid→liquid) or overcoming intermolecular forces (liquid→gas), not into increasing kinetic energy (temperature).
Why is latent heat of vaporization larger than fusion?
Vaporization requires breaking all intermolecular bonds and overcoming atmospheric pressure, while fusion only requires breaking the rigid structure. Typically L_v ≈ 5-7× L_f.
Does latent heat depend on temperature?
Yes, slightly. Latent heat decreases as temperature increases. However, for most practical purposes, it's treated as constant at the phase change temperature.
What happens to latent heat during reverse processes?
The same amount of energy is released. Freezing releases L_f, condensation releases L_v. This is why steam burns are so severe - condensation releases huge amounts of heat.
How is latent heat different from specific heat?
Specific heat (c) is energy to change temperature: Q = mcΔT. Latent heat (L) is energy to change phase at constant temperature: Q = mL. They're different processes.