AQA A Level Chemistry復習筆記1.4.1 Changes in State: Energy Changes
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
- Vaporization?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
Exam Tip
Be careful to match the bond breaking or making processes to the flow of energy during state changes. Remember that to break bonds, energy is always needed to overcome the forces of attraction between the particles
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