FORM 4: 4.3 UNDERSTANDING SPECIFIC LATENT HEAT

LATENT HEAT

Latent heat is the heat absorbed or the heat released at constant temperature during a change of phase.

The latent heat absorbed is used to break up the bonds between the particles.

LATENT HEAT OF FUSION

Latent heat of fusion is the heat absorbed by a melting solid.

LATENT HEAT OF VAPORISATION

Latent heat of vaporisation is the heat absorbed during boiling.

SPECIFIC LATENT HEAT, l

The specific latent heat of a substance, l is the amount of heat required to change the phase of 1 kg of the substance at a constant temperature.

SPECIFIC LATENT HEAT OF FUSION

The specific latent heat of fusion of a substance is defined as the amount of heat required to change 1 kg of the substance from solid to liquid phase without a change in temperature.

SPECIFIC LATENT HEAT OF VAPORISATION

The specific latent heat of vaporisation of a substance is defined as the amount of heat required to change 1 kg of the substance from liquid to gaseous phase without a change in temperature.

HEATING CURVE

Part	Change in temperature	Phase
AB	increase	solid
BC	unchanged	solid and liquid
CD	increase	liquid
DE	unchanged	liquid and gas

COOLING CURVE

Part	Change in temperature	Phase
PQ	decrease	gas
QR	unchanged	gas and liquid
RS	decrease	liquid
ST	unchanged	liquid and solid