Phase Change Calculator

Calculate energy requirements for phase transitions and temperature changes

Substance Properties

Select a substance or enter custom properties

kg
J/(kg·K)
J/(kg·K)
J/(kg·K)
J/kg
J/kg
°C
°C
Process Parameters

Define initial and final states

°C
°C
Total Energy Required
2,634,640 J
For the entire process
Sensible Heat
374,640 J
Temperature change energy
Latent Heat
2,260,000 J
Phase change energy
Solid
Liquid
Gas
0°C
100°C
120°C
Understanding Phase Changes

Phase changes occur when matter transitions between solid, liquid, and gas states.

  • Melting: Solid to liquid (absorbs energy)
  • Freezing: Liquid to solid (releases energy)
  • Vaporization: Liquid to gas (absorbs energy)
  • Condensation: Gas to liquid (releases energy)
  • Sublimation: Solid to gas (absorbs energy)
  • Deposition: Gas to solid (releases energy)
Phase Change Formulas
Q = m × c × ΔT (Sensible heat)
Q = m × L (Latent heat)
Where:
Q = Heat energy (Joules)
m = Mass (kg)
c = Specific heat capacity (J/kg·K)
ΔT = Temperature change (K or °C)
L = Latent heat (J/kg)
Water Phase Change Example

Heating 1kg of ice at -20°C to steam at 120°C:

  1. Heat ice from -20°C to 0°C: Q = 1 × 2100 × 20 = 42,000 J
  2. Melt ice at 0°C: Q = 1 × 334,000 = 334,000 J
  3. Heat water from 0°C to 100°C: Q = 1 × 4184 × 100 = 418,400 J
  4. Vaporize water at 100°C: Q = 1 × 2,260,000 = 2,260,000 J
  5. Heat steam from 100°C to 120°C: Q = 1 × 1996 × 20 = 39,920 J
  6. Total energy: 3,094,320 J
Phase Change Facts
  • During phase changes, temperature remains constant despite energy input
  • Water has unusually high latent heat values due to hydrogen bonding
  • Sweating cools us because evaporation requires heat energy
  • Pressure affects phase change temperatures (higher pressure = higher boiling point)
  • Dry ice sublimates directly from solid to gas at atmospheric pressure

About Phase Changes

Phase changes are transitions between different states of matter (solid, liquid, gas). During these transitions, heat is absorbed or released without changing temperature. This heat is called latent heat.

Phase Change Formula

Q = m × L

Where:

Q = Heat transferred (J or kJ)

m = Mass (kg)

L = Latent heat (J/kg or kJ/kg)

Types of Phase Changes

1

Melting (Fusion): Solid to liquid. Heat absorbed (endothermic).

Latent heat of fusion (Lf)

2

Freezing: Liquid to solid. Heat released (exothermic).

Magnitude: |Lf|

3

Vaporization: Liquid to gas. Heat absorbed (endothermic).

Latent heat of vaporization (Lv)

4

Condensation: Gas to liquid. Heat released (exothermic).

Magnitude: |Lv|

5

Sublimation: Solid to gas. Heat absorbed (endothermic).

Latent heat of sublimation (Ls)

6

Deposition: Gas to solid. Heat released (exothermic).

Magnitude: |Ls|

Key Concepts

Latent Heat
L
Heat per unit mass for phase change
Endothermic
Absorption
Heat absorbed during melting, vaporization, sublimation
Exothermic
Release
Heat released during freezing, condensation, deposition

Real-World Applications

Refrigeration

Phase changes in refrigerants absorb heat from surroundings

Sweating

Evaporation of sweat cools the body

Cooking

Water boiling and steam condensation

Note: During phase changes, temperature remains constant until the entire substance has changed phase. This is because the heat energy is used to overcome intermolecular forces rather than increase kinetic energy.

Substance Properties

Substance Melting Point (°C) Boiling Point (°C) Latent Heat (kJ/kg)
Water 0 100 334 (F)
2260 (V)
Ethanol -114 78 109 (F)
838 (V)
Oxygen -219 -183 14 (F)
213 (V)
Iron 1538 2862 247 (F)
6340 (V)
Mercury -39 357 11.4 (F)
296 (V)
Nitrogen -210 -196 25.7 (F)
199 (V)
Copper 1085 2562 205 (F)
4790 (V)
Silver 962 2162 105 (F)
2360 (V)
Gold 1064 2856 67 (F)
1700 (V)

Frequently Asked Questions

Latent heat is the energy absorbed or released by a substance during a phase change without a change in temperature. It's called "latent" because it doesn't cause a temperature change.

There are two main types:

  • Latent heat of fusion: Energy required to change from solid to liquid
  • Latent heat of vaporization: Energy required to change from liquid to gas

For water, the latent heat of fusion is 334 kJ/kg and latent heat of vaporization is 2260 kJ/kg.

Temperature remains constant during a phase change because the energy being added or removed is used to break or form intermolecular bonds rather than increase molecular kinetic energy.

During phase transitions:

  • For melting: Energy breaks the rigid bonds of the solid structure
  • For vaporization: Energy overcomes intermolecular forces to separate molecules
  • For freezing/condensation: Energy is released as bonds form

This phenomenon is why phase change graphs show horizontal lines at melting and boiling points.

Sensible heat and latent heat are two types of thermal energy transfer:

Sensible Heat Latent Heat
Changes temperature Changes phase (no temperature change)
Measured by temperature change Measured by mass change during phase transition
Formula: Q = m × c × ΔT Formula: Q = m × L
Example: Heating water from 20°C to 80°C Example: Melting ice at 0°C to water at 0°C

Pressure significantly affects phase change temperatures:

  • Boiling point: Increases with pressure (water boils at 120°C in a pressure cooker)
  • Freezing point:
    • Most substances: Increases with pressure
    • Water: Decreases with pressure (ice skating works because pressure melts ice)
  • Sublimation: Lower pressure favors sublimation (freeze-drying)

This is why phase diagrams show how melting and boiling points change with pressure.

The triple point is the unique combination of temperature and pressure where all three phases (solid, liquid, gas) coexist in equilibrium.

Key characteristics:

  • Represents the only conditions where solid, liquid, and gas can coexist
  • Phase boundaries converge at this point
  • Substance can transition directly between any two phases
  • For water: Triple point at 0.01°C and 611.657 Pa (0.006 atm)
  • Used as a reference point for temperature scales

Water has unusually high latent heat values due to its hydrogen bonding:

  • Strong intermolecular forces: Hydrogen bonds require more energy to break
  • Molecular structure: Bent shape creates polarity and stronger attractions
  • High specific heat: Related to its ability to absorb large amounts of heat

Comparison with other substances:

  • Water vaporization: 2260 kJ/kg
  • Ethanol vaporization: 841 kJ/kg
  • Ammonia vaporization: 1370 kJ/kg

This property makes water excellent for temperature regulation in biological systems and climate systems.