States of Matter

This simulation uses a real molecular dynamics model of 256 particles that attract at long range and repel at short range. At low temperature they lock into a regular crystal and only vibrate, at a middle temperature they slide past each other as a liquid, and at high temperature they fly apart as a gas. The model substance melts near 273 K and boils near 373 K. Particle colour shows speed, and readouts give the phase, temperature, number of neighbours and mean kinetic energy. It supports lessons on the particle model and changes of state.

• Start at 150 K and raise Temperature slowly to see where the crystal melts near 273 K.
• Keep going past 373 K and read the Phase readout when the liquid becomes a gas.
• Compare the Neighbours readout in the solid, liquid and gas states.
• Watch the particle colours change from blue to red as Mean KE increases.
• Set Gravity to 0 and then 1 to see how it affects the gas and the liquid.

1. 1Describe how particles are arranged and move in solids, liquids and gases.
2. 2Explain melting and boiling in terms of particle energy.
3. 3Relate temperature to the average kinetic energy of particles.
4. 4Use the number of neighbours to tell the state of matter.

Questions teachers ask