Why does temperature stay constant during a phase transition even as heat is added?

Energy goes into breaking intermolecular bonds (latent heat), not increasing KE.

Why do gases expand to fill their container but liquids don't?

Gas molecules have enough KE to overcome intermolecular attractions; liquid molecules don't.

Why does sweating cool you down? (evaporation).

Evaporation requires latent heat — energy is taken from your body, lowering its temperature.

Pro 🔒~15 min

States of Matter: Basics

Explore solid, liquid, and gas at the molecular level

How it works

Matter exists in solid, liquid, and gas phases depending on temperature and pressure. In a solid, molecules vibrate around fixed positions; in a liquid, they flow past each other; in a gas, they move freely. Phase transitions require energy (latent heat) without temperature change — energy breaks intermolecular bonds. The kinetic energy of molecules is proportional to absolute temperature (KE = 3/2 k_B T).

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Step-by-step

Use the temperature slider to heat or cool the substance.
Watch how molecular motion changes with temperature.
Observe the phase transition: molecules break free from their lattice at the melting point and escape the liquid at the boiling point.
The temperature-time graph shows the plateau during phase changes.

Key formulas

$KE_{avg} = \frac{3}{2}k_B T$ Average kinetic energy of molecules
$Q = mL$ Latent heat during phase transition

Frequently asked questions

Why does temperature stay constant during a phase transition even as heat is added?: Energy goes into breaking intermolecular bonds (latent heat), not increasing KE.
Why do gases expand to fill their container but liquids don't?: Gas molecules have enough KE to overcome intermolecular attractions; liquid molecules don't.
Why does sweating cool you down? (evaporation).: Evaporation requires latent heat — energy is taken from your body, lowering its temperature.