. MELTING, BOILING & EVAPORATION

8. MELTING, BOILING & EVAPORATION
Key notes:
1. Matter is made up of particles in a constant state of random motion.
2. At higher temperatures, particles in a solid vibrate more vigorously.
3. Inter-particles distance is greatest in gases and smallest in solids.
4. Melting occurs when a substance changes from the solid state to the liquid
state at a constant temperature, called its melting point.
5. During melting, the temperature remains constant even though heat energy is
continuously being supplied because this energy is used to bring about a
change in state.
6. When allowed to cool sufficiently, the substance will change from the liquid
state to the solid state. The constant temperature at which solidification occurs
is called the freezing point.
7. The melting point and freezing point of a substance are the same temperature.
8. Different substance have different melting points.
9. In a cooling curve, the freezing point or melting point of a substance is
indicated by the part of the curve which shows a constant temperature.
10. During freezing/melting, the substance exists in both the solid and liquid
states.
11. When heated, a liquid changes to the gaseous state at a fixed constant
temperature called its boiling point.
12. During boiling, the temperature remains constant because the heat energy
provided is used by the particles to escape from the liquid surface , i.e to bring
about a change of state.
13. Condensation occurs when a vapour is sufficiently cooled and changes to the
liquid state. Energy of the particles is given up to the surroundings.
14. The boiling point and condensation point of a substance are the same
temperature.
15. Evaporation causes cooling.
16. The rate of evaporation is affected by temperature, humidity, surface area and
the presence of wind.
17. Factors that raise the boiling point of a liquid are:
a) An increase in pressure
b) The presence of impurities
O LEVEL PHYSICS REVISION NOTES
18. Factors that lower the melting point of ice are:
a) An increase in pressure,
b) The presence of impurities.