Changes in State: Energy Changes (AQA A Level Chemistry)

State Changes

• Changes of state are physical changes that are reversible

• These changes do not change the chemical properties or chemical makeup of the substances involved

• Vaporisation includes evaporation and boiling

• Evaporation involves the change of liquid to gas, but unlike boiling, evaporation occurs only at the surface and takes place at temperatures below the boiling point

• Boiling occurs at a specific temperature and takes place when the vapour pressure reaches the external atmospheric pressure

State Changes

• The relationship between temperature and energy during state changes can be represented graphically

The relationship between temperature and energy during state changes

• Between 1 & 2, the particles are vibrating and gaining kinetic energy and the temperature rises

• Between 2 & 3, all the energy goes into breaking bonds – there is no increase in kinetic energy or temperature

• Between 3 & 4, the particles are moving around and gaining in kinetic energy

• Between 4 & 5, the substance is boiling, so bonds are breaking and there is no increase in kinetic energy or temperature

• From 5 & 6, the particles are moving around rapidly and increasing in kinetic energy