States of matter

Matter can be classified in terms of three interconvertible states of matter: solid, liquid and gas1

State	Arrangement of molecules	Force of attraction between molecules
Solid	Held in a rigid lattice	Very strong
Liquid	Held together loosely, but are free to move past each other	Weaker: this allows liquids to flow
Gas	Free to move, travelling rapidly in a straight line until colliding	None: the large distances between the molecules allow the gas to change volume

Phase transitions
1. Melting is from solid to liquid; freezing is from liquid to solid
2. Vaporisation is from liquid to gas; condensation is from gas to liquid
3. Sublimation is from solid to gas; deposition is from gas to solid
Diffusion
1. Everything is made of particles, whose existence is evident by the phenomenon of diffusion, whereby the random movement of particles of a fluid causes a net movement from an area of high concentration to an area of low concentration
2. Bromine gas is a brown gas that diffuses in air
3. Potassium permanganate KMnO₄ is a purple crystal that diffuses in water to form a magenta-rose solution, though, being in a liquid, at a slower rate than in a gas
4. Ammonia and hydrogen chloride are gases that diffuse in air, so when placed at either ends of a tube, travel down the tube until they meet, reacting to form a white surface of ammonium chloride: NH_{3 (g)} + HCl_(g) → NH₄Cl_(s); since hydrogen chloride molecules are heavier than ammonia ones, and speed of diffusion is inversely proportional to mass, the surface forms closer to the hydrogen chloride end