5 • Quantity of Heat - Latent Heat

Define Latent Heat (L)

The amount of heat required to change the state of a body

Define the SI Unit for Latent Heat (L)

J

Label This Formula

Energy Needed to Change State (Latent Heat)

heat added or removed

L - latent heat

Define Specific Latent Heat (l)

The amount of heat required to change the state of 1kg of a body

Define the SI Unit for Specific Latent Heat (l)

Jkg-1

Label This Formula

Energy Needed to Change State (Specific Latent Heat)

heat added or removed

m - mass

l - specific latent heat

What page of the log tables can you find the Energy Needed to Change State Formulae?

58

Define Specific Latent Heat of Fusion

The amount of heat required to change 1kg of a solid to 1kg of a liquid at its melting point

Label This Diagram

The Latent Heat Scale

a - temperature (°C)

b - time (s)

c - 0°C

d - 100°C

e - latent heat of fusion

f - liquid

g - latent heat of vaporisation

h - steam

Define Specific Latent Heat of Vaporisation

The amount of heat required to change 1kg of liquid to 1kg of vapour at its boiling point

Demonstrate the process of Perspiration

• Water evaporates from skin surface

• Removes latent heat

• Cools us down

Label This Diagram

The Heat Pump

a - cold

b - hot

c - compressor

d - valve

e - gas

f - liquid

Demonstrate the process of the Heat Pump

• Liquid expands at valve into gas

• Taken in latent heat

• Gas compresses at compressor to liquid

• Gives out latent heat