P3 - Specific Latent Heat

What is specific latent heat?

The amount of energy required to change the state of 1 kg of a substance with no change in temperature.

When does temperature stay constant during heating?

During a change of state (e.g. melting or boiling).

What happens to energy during a change of state?

It is used to break or weaken intermolecular forces, not to increase temperature.

What is the specific latent heat of fusion?

The energy needed to change 1 kg of a substance from a solid to a liquid with no change in temperature.

What is the specific latent heat of vaporization?

The energy needed to change 1 kg of a substance from a liquid to a gas with no change in temperature.

What is the equation for energy change during a change of state?

Energy = mass × specific latent heat

What are the units for energy in the latent heat equation?

Joules (J)

What are the units for mass in the latent heat equation?

Kilograms (kg)

What are the units for specific latent heat?

Joules per kilogram (J/kg)

What must happen to the particles during melting or boiling?

The particles must overcome or break the forces of attraction between them.

Why is no temperature change seen during melting or boiling?

Because energy goes into breaking intermolecular forces instead of increasing kinetic energy.

Is the specific latent heat equation given in the exam?

Yes, the equation is provided in the AQA Physics and Combined Science formula sheet.

Do you need to memorise specific latent heat values for different substances?

No, you will be given any required values in the exam.

How much energy is needed to melt 1 kg of ice?

334,000 J (this is the specific latent heat of fusion for water).

How do you calculate energy needed to boil a liquid?

Multiply the mass by the specific latent heat of vaporization.

What's the key difference between specific heat capacity and specific latent heat?

Specific heat capacity involves temperature change; specific latent heat involves a change of state with no temperature change.

Why does boiling require more energy than melting for the same substance?

Because more energy is needed to completely separate particles during vaporization than to allow them to slide past each other during melting.