The diagram summarises the common changes of state.
Evaporation can take place below the boiling point 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 evaporation is at its maximum.
Energy must be transferred from a substance to the environment for these changes of state to happen. This is because forces of attraction form between the particles.
The state of a substance at a given temperature can be predicted if its melting point and boiling point are known. The table summarises how to work this out.
|Given temperature < melting point||Solid|
|Given temperature is between melting and boiling points||Liquid|
|Given temperature > boiling point||Gas|
The melting point of oxygen is -218°C and its boiling point is -183°C. Predict the state of oxygen at -200°C.
Oxygen will be in the liquid state at -200°C (because this is between its melting and boiling points).
The element bromine has a melting point of -7°C and a boiling point of 59°C. Predict the state of bromine at room temperature.
Bromine will be in the liquid state at room temperature, because this is between its melting and boiling points (room temperature is usually around 20°C).