States of matter simulation

A states of matter simulation shows the particles of a substance as a solid, a liquid and a gas, and what happens to them when you heat or cool it. In our States of Matter Simulator, hundreds of particles attract each other in a box under a weighted lid. Nothing is scripted: the crystal melts, the liquid boils and the lid rises because of how the particles move, and the flat plateaus of a heating curve appear by themselves.

It opens on solid water, ice, with the heater on. Press play and watch the lattice shake apart.

Try it

States of Matter Simulator

Heat and cool particles and watch them change state

Open the simulatorGo to its page

How to use the states of matter simulator

1. Under Substance and heat, choose a substance: water, nitrogen, oxygen, ethanol or mercury.
2. Set the Heater. To the right it heats, to the left it cools, and in the middle it is off.
3. Press play under Run. Particles are coloured by what they are doing: held in a lattice, moving like a liquid, or flying free like a gas.
4. Watch the readouts: the temperature in kelvin, the state, the heater setting and the height of the lid.
5. Watch the heating curve draw itself: temperature against heat added. Use Start again as a solid, liquid or gas to begin from another state.

The panel lists the substance's real melting and boiling points at 1 atm, and its enthalpies of fusion and vaporisation. Practice and help sets questions on states, plateaus and the energy to melt or boil a mass, with worked solutions.

Solids, liquids and gases: the particle model

The hotter a substance, the faster its particles move on average. Heating gives them more energy, so a solid vibrates harder until its particles break out of the lattice and melt, and a liquid's fastest particles break free and boil.

Reading the heating curve

As you heat a solid, its temperature rises, then stays flat while it melts, rises again, and stays flat again while it boils. On each flat part, the plateau, the energy goes into breaking the attractions between particles, not into making them move faster, so the temperature does not change until the change of state is complete.

• First plateau: melting, at the melting point. Water melts at 273.15 K (0 °C).
• Second plateau: boiling, at the boiling point. Water boils at 373.15 K (100 °C) at 1 atm.
• Longer plateau for boiling: boiling separates the particles completely, which takes far more energy than loosening the lattice. For water, 40.7 kJ/mol against 6.01 kJ/mol.

Turn the heater to cooling and the curve runs the other way: the gas condenses and the liquid freezes, giving out the same energy at the same temperatures. Check your reading:

Worked examples

Example 1: what state is it in?

Ethanol melts at 159 K and boils at 351.4 K. At 200 K it is between the two, so it is a liquid. Nitrogen boils at 77.36 K, so at room temperature, about 293 K, it is a gas. Mercury melts at 234.3 K, so it is a liquid at room temperature, as in old thermometers. Choose each substance and the panel shows these values.

Example 2: the energy to melt ice

How much energy does it take to melt 36 g of ice at 0 °C? The molar mass of water is 18.02 g/mol and its enthalpy of fusion is 6.01 kJ/mol:

Example 3: the energy to boil water

Boiling 50 g of water at 100 °C takes 50 ÷ 18.02 × 40.7 = 113 kJ, more than nine times as much as melting the same mass. In physics, the same data appear as specific latent heats: 6.01 ÷ 18.02 = 0.334 kJ/g, or 334 kJ/kg, for melting ice, and 2,260 kJ/kg for boiling water. Our specific latent heat guide covers that version.

What the simulator does not show

• A model, not a picture of real molecules. The particles are round and attract each other in one simple way. The model is tuned so each substance melts and boils at its real temperatures, but its particles are not shaped like water or ethanol molecules.
• Fixed pressure. The weighted lid keeps the pressure steady, so it shows changes at 1 atm, not how boiling points change with pressure.
• No sublimation or plasma. It covers solid, liquid and gas.

Common mistakes

• Saying the temperature rises during melting. It stays flat until the whole solid has melted.
• Saying particles expand when heated. The particles stay the same size; the spaces between them grow.
• Confusing evaporation and boiling. Evaporation happens from the surface at any temperature; boiling happens throughout the liquid at the boiling point.
• Forgetting kelvin. K = °C + 273.15, so water boils at 373.15 K.

Practise particles in a short timed paper

States of matter and heating curves come up in Grade 8 Physical Science: Chemistry practice, and latent heat in High School Physics. In the UK they appear in GCSE Chemistry Foundation and GCSE Physics Higher. Each daily paper is a short timed paper of 8 questions worth 25 to 35 marks, and the papers mix topics.

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