Library / Foundations: Physics / FPH-16
Foundations: Physics
Specific latent heat
Energy to change the state of a mass at constant temperature.
- Ref
- FPH-16
- Rev
- v1
- Field
- Foundations: Physics
- Result
- E [kJ]
Use specific latent heat L in J/kg for a change of state at constant temperature.
Melting or boiling needs energy that goes into breaking bonds, not raising the temperature.
Calculator
kJ
kg
kJ/kg
- Energy in joules83,500 J
- Equivalent temperature rise of the same mass of water79.9 K
What drives the result
Each variable is moved across its typical range while the others stay at the values above. The longest bar is the key driver.
Energy (kJ) current value 83.5 kJ
mMassKey driver
3.3433,400
LSpecific latent heat
25575
- Boiling water takes about seven times more energy per kg than heating it from 0 °C to 100 °C.
- The temperature stays constant during the change of state.
Chart data as tables
Ranked variables
| Variable | Typical range | Lowest result | Highest result | Swing (kJ) | Local step | Change in result |
|---|---|---|---|---|---|---|
| m Mass | 0.01 to 100 kg | 3.34 | 33,400 | 33,400 | +10% | +10 % |
| L Specific latent heat | 100 to 2,300 kJ/kg | 25 | 575 | 550 | +10% | +10 % |
Sweep of Mass
| Mass (kg) | Energy (kJ) |
|---|---|
| 0.01 | 3.34 |
| 0.03162 | 10.56 |
| 0.1 | 33.4 |
| 0.3162 | 105.6 |
| 1 | 334 |
| 3.162 | 1,056 |
| 10 | 3,340 |
| 31.62 | 10,560 |
| 100 | 33,400 |
Sweep one variable
Energy (kJ)Hover, touch, or use the arrow keys on the chart
Variables and how each one contributes
E
Energy
What the equation gives you. Everything else feeds it.
m
Mass
Mass changing state. Directly proportional.
L
Specific latent heat
Ice melting 334, water boiling 2260. Directly proportional.
Worked example with the values above
- Mass 0.25 kg, latent heat 334 kJ/kg.
- Multiply: 0.25 × 334.
- E = 83.5 kJ.
Assumptions and limits
- Temperature constant during the change.
- Pure substance.
Common mistakes
- Using specific heat instead of latent heat.
- Mixing J and kJ.
Statistics and uncertainty
Latent heat values vary by a percent or two between sources and with pressure.
Where it is used
- Energy to melt or vaporise a coolant or fuel.
- Cooling by evaporation.
Maths you need
- States of matter: solid, liquid, gas
- Energy: joules