Internal energy is made up of kinetic energy and potential energy.
9.2 Melting and Solidification
Melting is the change of state from solid to liquid, without a change in temperature
During melting, the temperature remains constant at the melting point.
Thermal energy is absorbed by the substance.
Solidification is the change of state from liquid to solid, without a change in temperature.
During solidification, the temperature remains constant at the freezing point.
Thermal energy is released by the substance.
9.3 Boiling and Condensation
Boiling is the change of state from a liquid into vapour, occurring at a constant temperature called the boiling point.
During boiling, the temperature remains constant at its boiling point.
Thermal energy is being absorbed by the substance.
Condensation is the process whereby vapour changes into liquid at the same constant temperature. Heat is given out during condensation.
During condensation, the temperature remains constant at the condensation point. Thermal energy is released by the substance.
9.4 Evaporation
Factors affecting the rate of evaporation
- Temperature
- Humidity of the surrounding air
- Surface area of the liquid
- Movement of air
- Pressure
- Boiling point of the liquid
Heating a liquid will increase the rate of evaporation because it means a greater number of molecules at the surface layer are energetic enough to escape.
2. Humidity of the surrounding air
Rate of evaporation decreases with increasing humidity (Water vapour present in the air).
3. Surface area of the liquid
Larger surface area = Increase in evaporation
4. Movement of air
Rate of evaporation increases when the surrounding air is moving.
Moving air removes the molecules of the liquid as soon as they escape from the surface of something.
5. Pressure
Reducing the atmospheric pressure increases the rate of evaporation.
Example: Things can dry faster on mountaintops than at sea level.
6. Boiling point of the liquid
Liquids with lower boiling point evaporates faster.
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