1. Thermal Physics IGCSE Revision Lectures 1.The Kinetic Model of Matter 2.Heat versus Temperature 3.Measuring Temperature 4.Heat Processes 5.Heat Capacity 6.Latent Heat

2. 1. The Kinetic Model of Matter All matter is made of atoms or molecules. These have energy. This energy is found in the chemical bonds and in their kinetic energy. Their chemical energy defines the state of the material The kinetic energy defines their temperature, pressure and volume.

3. Particles What happens to the kinetic energy of the particles when a gas is heated? The heat energy is transferred to the kinetic energy of the gas particles. What sort of graph would you get if you plotted ‘Kelvin temperature (T k )’ against ‘the average kinetic energy (KE ave )of the particles’. Zero Kelvin temperature equals zero gas molecule kinetic energy. At what temperature is zero Kelvin? -273°C TkTk KE ave

4. Pressure(P) and temperature(T) T P P  T As long as it is Kelvin temperature P – pressure (Pascals) T – Temperature(K) P 1 /T 1 = P 2 /T 2 Recall: (P = F/A)

5. 2. Heat versus Temperature These are NOT the same thing. Heat is a type of energy. It flows from a hot place to a cold. Temperature is a measure of the average kinetic energy of the molecules.

6. 3. Measuring Temperature

7. Boiling Boiling occurs when vapour is produced in the body of the liquid. The bubble contains only water vapour, not air!

8. Evaporation Since the average speed of the remaining molecules must now be lower, the temperature of the liquid drops (since temperature is a measure of the kinetic energy of the molecules).

9. 4. Heat Processes

10. Heat can travel by Conduction Hot particles vibrate more, so collide with adjacent particles. The heat energy travels from hot to cooler areas. hot cold

11. 1.Conduction in metals  Metals have atoms inside them and lots of free electrons.  The free electrons can move around and vibrate.  The heat energy is passed on by neighbouring particles vibrating along the metal.  There are too few free electrons in a non-metal for this to happen. Energy : heat transfer

12. 4.Radiation Heat can move by travelling as Infra Red waves These are electromagnetic waves, like light waves, but with a longer wavelength. This means that infra red waves act very much like light waves:  They can travel through a vacuum  They travel at 300,000,000 m/s  They can be reflected  They can ’ t travel through opaque materials. Energy : heat transfer

13. Infrared radiation Infrared radiation can travel through a vacuum (and through air)

14. 2.Why does take-away food often come in aluminium containers? 3.Why do elephants have big ears? 4.Radiation Energy : heat transfer 1.How does a cup of tea lose heat by conduction, convection, evaporation and radiation?

15. 5. Heat Capacity This is the measure of a substance’s capacity to absorb heat. A large heat capacity means the substance can absorb a lot of heat but only change temperature by a small amount. E H = c.m.(T f – T i )

16. 6. Latent Heat

17. Latent heat When the molecules of a substance settle into the regular patter of a solid, energy is released as bonds are formed. This energy released is called latent heat. This stops the temperature from falling. (“latent” = “hidden”)

18. Solid  Liquid Liquid Liquid  Gas Gas Solid Temperature Time Melting  Freezing  Boiling  Condensing  Changes of State

19. Example The specific latent heat of fusion (melting) of ice is 334 000 J/kg. How much energy is needed to melt 5kg of ice at 0°C to 5 kg of water at 0°C? Energy = mL = 5 x 334 000 = 1670000 J