3.2 Internal energy

Question 1

Internal energy

Answer 1

The total energy (kinetic + potential) stored inside a system by the particles that make up the system due to their motion and positions.

Question 2

Specific heat capacity

Answer 2

ΔE = mcΔt

ΔE = change in energy, in joules (J)
m = mass, in kilograms (kg)
c = specific heat capacity, in joules per kilogram per degree Celsius (J/kg °C)
Δt= change in temperature, in degrees Celsius (°C)

The amount of energy required to raise the temperature of 1 kg of the substance by 1 °C

Question 3

Latent heat

Answer 3

The energy needed for a substance to change state is called the latent heat
When a change of state occurs, the energy transferred to or away from a substance changes the internal energy of the substance but not its temperature.
This means that whilst the substance is changing state (e.g. from liquid to gas), the temperature of the substance remains constant, despite the fact that energy is still being transferred to the substance.
This is because the energy is being used to overcome intermolecular forces of attraction between the molecules instead of increasing the kinetic energy of the molecules (and hence the temperature).

Question 4

Specific latent heat

Answer 4

The amount of energy required to change the state of 1 kg of a substance with no change in temperature.
There are two types of specific latent heat:
Specific latent heat of fusion and vaporisation.
E = mL

E = thermal energy required for a change in state, in joules (J)
m = mass, in kilograms (kg)
L = specific latent heat, in joules per kilogram (J/kg)

Question 5

Latent heat of fusion

Answer 5

The energy required to convert 1 kg of a substance between a solid and a liquid state with no change in temperature.
This applies when melting a solid or freezing a liquid.

Question 6

Latent heat of vaporisation

Answer 6

The energy required to convert 1 kg between a liquid and a gaseous state with no change in temperature.
This applies when vaporising a liquid or condensing a gas