Change of state
The diagram summarises the common changes of state.
Explaining change of state
Melting, evaporating and boiling
The capacity of a system to do work or the quantity required for mechanical work to take place. Measured in joules (J). For example, a man transfers 100 J of energy when moving a wheelbarrow. must be transferred, by heating, to a substance for these changes of Solid, liquid or gas. Evaporation is a change of state from liquid to gas. to happen. During these changes the A general term for a small piece of matter. For example, protons, neutrons, electrons, atoms, ions or molecules. gain energy. This is used to overcome A push or a pull. The unit of force is the newton (N). of When two or more things come together, eg the north pole of a magnet is attracted to the south pole of a magnet. between particles:
- some of these forces are overcome during The process that occurs when a solid turns into a liquid when it is heated.
- all of the remaining forces are overcome during The process in which a liquid changes state and turns into a gas. or boiling
Evaporation can take place below the The temperature at which a substance rapidly changes from a liquid to a gas. of a substance. This is why damp clothes dry when they are hung from a washing line. Boiling happens at the boiling point, when the rate of The process in which a liquid changes state and turns into a gas. is much faster.
Condensing and freezing
Energy must be transferred from a substance to the environment for A change of state in which gas becomes liquid by cooling. and A change of state in which liquid becomes solid by cooling. to happen. During these changes of state the particles lose energy as forces of attraction form between them.
Limitations of the particle model 鈥 Higher tier
The particle model does not take into account:
- the size and shape of particles
- the space between particles
For example, at room temperature and pressure, the distance between helium atoms is over 50 times more than the diameter of helium atoms. This is much more than you normally see in diagrams.
In addition, the particle model does not take into account the forces between particles. For example, some weak forces of attraction remain between particles in the gas state.