Home / Learn / Chemistry / States of matterTool #L28 (formerly #1064)

States of matter

Heat or cool water, ethanol, oxygen or iron and watch the particles vibrate in place, slide past each other or fly apart. Stop at the melting and boiling points, change °C to kelvin, and race diffusion in liquids and gases.

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A teaching model: the particles are drawn far bigger and far fewer than real ones, and their motion is a cartoon of how real particles behave, not a simulation of the forces between them. Melting and boiling points are rounded values at normal air pressure.

Try this

  • Heat ice from −40 °C. The particles shake harder and harder, then break out of their pattern at 0 °C.
  • Stop exactly at 0 °C or 100 °C: two states live together while the substance melts or boils.
  • Compare ethanol with water: ethanol boils at a much lower temperature, so its particles escape more easily.
  • Oxygen is a gas in the room; you would need to cool it below −183 °C to make it liquid.
  • In Diffusion, time a cold liquid and a hot gas. Hotter particles move faster, so they mix sooner.

Check yourself

What it does

Everything is made of tiny particles that are always moving. How strongly they hold on to each other, and how fast they move, decides whether a substance is a solid, a liquid or a gas. This page puts a few particles in a box and lets you heat or cool them. In a solid they only shake about fixed places; heat them to the melting point and they break free and slide past each other as a liquid; heat them to the boiling point and they fly apart as a gas that fills the box. A second view shows diffusion: two colours of particles spreading into each other once a divider is lifted.

It follows the school topics on matter: Class 8 Science, the particulate nature of matter (states of matter and the particle model), and Class 9 Science, Matter in Our Surroundings (characteristics of particles, states of matter, change of state, melting and boiling points, the kelvin scale, diffusion and evaporation). Next, heating curve shows why the temperature stops rising while ice melts, and kinetic theory shows how gas particles make pressure. For the maths of particles wandering, see random walk.

How to use it

  1. Pick a substance. Its rounded melting and boiling points are shown under the slider.
  2. Press Heat (+10 °C) or Cool (−10 °C), or drag the temperature slider. The buttons stop exactly at the melting and boiling points so you can see two states together.
  3. Read the state, the spacing of the particles and how they move. Switch the Level to Class 9 to add the temperature in kelvin and the average energy of a particle.
  4. Choose Diffusion, pick gases or liquids and a temperature, and press Lift the divider. The page shows how mixed the colours are and how many seconds they took to reach 80%. Start again puts the divider back.
  5. Pause freezes the particles.

Worked example

The page opens with water at 20 °C: a liquid. Press Cool twice: at 0 °C the water is at its melting point, part solid and part liquid; once more and it is ice at −10 °C, with its particles locked in a pattern. Heat it back up and keep going: at 100 °C it boils, and at 110 °C it is steam.

On the Class 9 level at 20 °C the page shows 293 K (20 + 273; 293.15 K with the exact 273.15) and an average particle energy of (3/2)kT = 6.07 × 10⁻²¹ J. At 313 K (40 °C) the energy is about 7% higher, and it would double at 586 K.

Check yourself

Five questions, fresh each time: change °C to kelvin and back, decide the state of a substance from its melting and boiling points, a question about the particle model, and one about diffusion. Nothing is saved.

Tips

  • During melting and boiling the temperature stays the same even though you keep heating: the heat goes into pulling particles apart (latent heat).
  • Evaporation happens at any temperature, from the surface only; boiling happens all through the liquid at the boiling point.
  • Gases diffuse much faster than liquids because their particles move freely and have lots of space between them.

FAQ

Are real particles this big? No. A drop of water holds about 10²¹ particles. The picture uses a few dozen, drawn huge, and a simple made-up motion that shows the idea.

Why do the boiling points change on a mountain? Lower air pressure lets particles escape more easily, so water boils below 100 °C. The page uses normal air pressure.

Is this from NCERT? No. It is an independent study aid that follows the same school topics, with its own pictures and numbers.

Where the numbers come from

  • Particle model of solids, liquids and gases, melting and boiling at constant temperature, Kelvin scale K = °C + 273.15, mean kinetic energy (3/2)kT with the Boltzmann constant k = 1.380649 × 10⁻²³ J/K (SI, exact), diffusion faster at higher temperature: standard science.
  • Melting and boiling points at normal pressure are rounded general values: water 0 and 100 °C, ethanol −114 and 78 °C, oxygen −218 and −183 °C, iron 1,538 and 2,862 °C.
  • The particle motion is a teaching cartoon written for this page (seeded random kicks, a soft push between particles), checked by tests that solids stay near their places, liquids stay in the bottom, gases fill the box and two gases mix once the divider is lifted.

Standard scientific values, such as constants, atomic weights and melting points, are facts found in every textbook; we name where ours were checked. If you are an author or publisher and want a value, a credit or a table changed or removed, tell us and we will act quickly.

Last updated 2026-11-09.

Change log for States of matter

  1. Add #1066 Gas in a box Details on GitHub
  2. Add #1064 States of matter particle box Details on GitHub

Every change to fibub

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