Particles spread out from where they are in high concentrations to where they are in lowconcentrations
Diffusion is evidence that something spreads out – this something is a particle
Coloured compounds can be diluted many times before the colour disappears, which is evidence that particles must be very small
States of matter
Solids
Liquids
Gases
A substance can usually exist in all three states, dependent on temperature (and pressure)
Melting
Solid → Liquid (when heating up)
Freezing
Liquid → Solid (when cooling down)
Boiling
Liquid → Gas (when heating up)
Condensing
Gas → Liquid (when cooling down)
Solid
Close arrangement, Ordered, Vibrate around fixed positions
Liquid
Close arrangement, Random, Move freely past each other
Gas
Far apart arrangement, Random, Move completely freely
Melting of a solid
Particles gain kinetic energy, moving faster, until they have enough energy to overcome the forces holding them together and start to move past each other forming a liquid
Boiling of a gas
Particles lose kinetic energy, moving more slowly, forces of attraction start to form between the particles, the forces start to hold the particles together as a liquid
Ammonium Chloride Tube
Two gases, ammonia and hydrogen chloride, diffuse from the ends of the sealed tube, where they meet the compound ammonium chloride forms as a white smoke
The hydrogen chloride molecules must be heavier, as they diffused slower
If you heat up the tube
The white smoke forms faster because the particles move faster and collide more often