Solids, Liquids and Gases
All materials can exist in different states of matter depending upon temperature and pressure. The three states of matter are solid, liquid and gas, and they have different properties.
Solids have a definite volume and shape, high density, not compressible, low expansion on heating, cannot flow and movement of particles slow.
Liquids have a definite volume but no definite shape, medium density, slightly compressible, medium expansion on heating, flow easily and movement of particles medium.
Gases have no definite volume and no definite space, low density, easily compressed, large expansion on heating and flow/diffuse easily and fast movement of particles.
Particle Theory
The particle theory provides a theory to explain the different properties of solids, liquids and gases. It assumes that the particles in a substance stay the same whether it's a solid, a liquid or a gas; and what changes is the arrangement of the particles and their energy:
Solid - the particles arranged regularly with strong forces between particles; particles only vibrate
Liquid - particles arranged irregularly with strong forces between particles; particles move more than in solids
Gas - irregular arrangement of particles with no/very weak forces between particles; particles move rapidly
Generally particles are more closely packed in solids than in liquids, and more closely packed in liquids than in gases. There are two implications of this. The first is that solid is more dense than liquid which is in turn more dense than gas. The second is that the spacing between the particles has an effect on the particles movement. In a solid, the particles only vibrate about their fixed positions. In a gas, the particles are moving rapidly and in all directions, collide frequently with each other and with the walls of the container. In liquids there is more movement of particles than in solids but less movement than in gases. There is no pattern to the movement of particles in solids, liquids and gases. The particles are in random movement.
Changes of State
Change of state does not change the particles of the substance, just their arrangement or energy level.
When a solid is heated, its particles gain more energy which makes the particles move more, weakening the forces holding the soild together. This makes the solid expand. At the melting point, the particles have enough energy to break free from their positions and the solid turns into a liquid.
When a liquid is heated, the particles get even more energy. This energy makes the particles move faster which weakens the bonds holding the liquid together. At the boiling point, the particles have eneough energy to break their bonds and the liquid turns into a gas.
Soild ----melting----> liquid ------boiling------> gas
Solid <---freezing--- liquid <---condensing--- gas
A solid can sublimate into a gas and the gas resublimate into a solid. The is known as sublimation and desublimation respectively.
When a gas in a sealed container is heated, both the gas temperature and the gas pressure are raised. The gas pressure is due to the particles hitting a surface. The particles are moving very fast and randomly in all directions and bouncing off the walls of the container so there is pressure on the sides of the container.
Evaporation and Diffusion
Evaporation is like boiling and involves a change from liquid to gas but occurs at any temperature, not necessarily at the boiling point. Evaporation is when some of the particles near the surface of the liquid gained enough energy to break free and turns into a gaseous state.
Diffusion is the movement of particles to fill in any space available. Diffusion does not involve a change in state and is just particles spreading out. Diffusion occurs only in gases and liquids except the process is much more slowly in liquids because the particles in a liquid are moving moe slowly than in a gas, and that the particles in a liquid are closer together slowing the spreading.