Lessons · Teaching · states of matter, and what changes between them
Same particles, different arrangement
Solid, liquid and gas are the three states of matter. In a solid the particles are close and fixed in place, in a liquid they are close but able to slide, and in a gas they are far apart and moving freely. Heating gives particles more energy and can change the state; the particles themselves never change.
Hone is a place to practise a career, one idea a day. This is one of its lessons, written out in full and free to read without an account.
In beta. This lesson was written for Hone and has not yet been checked by a state certification officer. Practice material, not professional advice. What that means.
What it is for
Ice, water and steam being the same substance is the idea, and it is what makes melting and boiling reversible while burning is not. A pupil who thinks steam is a different substance from ice cannot make sense of the water cycle they learned two lessons ago.
How to think about it
Describe any change of state by what happened to the particles, not by what happened to the appearance. Name the change in both directions: melting and freezing, evaporating and condensing, and sublimation where a solid goes straight to a gas.
Worked example
Solid: particles close together in a fixed arrangement, vibratingFixed shape and fixed volume.
Liquid: close together but free to move past each otherFixed volume, takes the shape of the container.
Gas: far apart and moving freely in all directionsNeither shape nor volume is fixed.
Melting, freezing, evaporating, condensing and sublimation are all reversibleThe substance is the same throughout, which is why they reverse.
Your turn
Name the state in which particles are close together but can slide past each other.
Particles slide past one another in a
Solve one, graded on the server
The trap
Saying particles expand when heated. The particles stay the same size and move further apart or faster. It is the substance that expands, not the particles in it.