6.2.1

# Thermal Energy Transfer

Test yourself

## Internal Energy

Internal energy is the sum of the randomly distributed kinetic energies and potential energies of all the particles in a gas.

### Particle energies

• Kinetic energy comes from the random movements of particles in a gas.
• Potential energy comes from the interactions between the particles.

• The internal energy can be increased by adding energy to the system.
• If you add heat to a system it increases in energy but NOT always in temperature.

## Specific Heat Capacity

The specific heat capacity is the amount of energy needed to raise one kilogram of material by 1 degree Kelvin.

### Heat capacity

• Energy required = mass x specific heat capacity x change in temperature
• $Q=mc{\Delta\theta}$

### Temperature

• All temperatures should be calculated in Kelvin.
• For changes in temperature, the change in degrees is the same as the change in Kelvin.

## Specific Latent Heat

The energy required to change the state of an object is the specific latent heat.

### Changing state

• To make an object go from a solid to a liquid or a liquid to a gas you need to add some energy. This energy is the latent heat.
• The energy goes into weakening the intermolecular bonds NOT into changing the temperature. The equation for the energy is:
• The energy needed = mass x specific latent heat
• $Q=ml$

### Kinetic energies

• When the latent heat is added to a solid to melt it, the bonds between molecules are weakened.
• Because all of the energy goes into weakening the bonds, there is no gain in kinetic energy and there is no gain in temperature.