States of Matter – Interactive PhET Simulation

Explore states of matter

The physical state of a substance depends on the arrangement, movement and interactions of its particles and on the conditions of temperature and pressure.

This interactive PhET simulation allows you to observe particles in the solid, liquid and gaseous states, heat and cool substances, and investigate what happens at the particle level during changes of state. PhET’s current HTML5 version also allows students to explore the effects of temperature and pressure.

Look at what the particles are actually doing. Compare their arrangement and movement in each state, then predict what will happen before heating, cooling or changing the pressure. Use the particle model to explain the macroscopic changes you observe.

 
 
 

States of Matter is provided by PhET Interactive Simulations, University of Colorado Boulder, and is used under the CC BY-NC 4.0 licence.

Try these challenges

1. Compare the three states
Observe the particles in a solid, liquid and gas. Compare their arrangement, separation and movement.

2. Heat a solid
Gradually increase the temperature. What happens to the movement of the particles before the substance melts?

3. Investigate melting
Watch what happens as the solid becomes a liquid. The particles themselves have not changed — so what has changed?

4. Produce a gas
Continue heating. Compare the separation and movement of the particles in the gas with those in the liquid.

5. Reverse the changes
Cool the substance again. Can you observe condensation and freezing? Explain these changes in terms of particle energy and intermolecular attractions.

6. Change the pressure
Investigate the effect of changing pressure. Under what conditions can increasing pressure encourage particles to move closer together?

7. Explore intermolecular attractions
Use the Interaction Potential section to investigate how potential energy varies with particle separation. Look for the separation corresponding to minimum potential energy.

The key question

Keep asking:

How does the balance between particle kinetic energy and attractive forces determine the physical state of a substance?

The particles themselves do not become solid, liquid or gaseous — it is their arrangement, separation and movement that change.

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