States of Matter

How to use it

Choose a substance, then press Heat and watch. The particles start locked in a solid, vibrating in place. Keep heating and they break free and slide past each other as a liquid, then fly apart as a gas. Press Cool to run it backwards, or Fast ×5 if boiling is taking too long. The graph draws the heating (or cooling) curve as you go.

Before heating, ask students to sketch what they think the graph will look like. Then compare. The flat parts surprise almost everyone.

Why the graph goes flat

All matter is made of tiny particles that are always moving. Temperature is a measure of how fast they move on average. In a solid the particles are held tightly in place and can only vibrate. In a liquid they are still close together but can slide past one another, so a liquid flows and takes the shape of its container. In a gas they are far apart and zoom around freely, filling the whole container.

While a solid is melting, the heat goes into breaking particles free from their places, not into making them move faster, so the temperature stays at the melting point until it has all melted. The same thing happens at the boiling point, and that plateau is much longer because pulling particles completely apart takes far more energy: boiling a gram of water away takes about five times the energy needed to warm it from 0 °C to 100 °C. Cooling runs the same steps in reverse: condensing and freezing give that energy back.

Melting and boiling points shown are at normal air pressure: water 0 °C and 100 °C, ethanol −114 °C and 78 °C, nitrogen −210 °C and −196 °C. Real liquids also evaporate slowly below their boiling point; this simulation shows only boiling. The box shows a handful of particles; a real drop of water holds more than a billion trillion.

Free to use, no account needed. It runs in your browser: nothing you type, and no sound from your microphone, is sent to Fieldbook.