4.3 UNDERSTANDING SPECIFIC LATENT HEAT

CHANGE OF PHASE & LATENT HEAT

The change of one phase to another phase of matter happens at a SPECIFIC TEMPERATURE and

PRESSURE. The change happens with the ABSORPTION or RELEASE of heat followed by a

change in the volume and density of the substance

MATTER

LIQUID GASSOLID

Total energy absorbed or released when a substance changes its physical state

completely at a constant temperature.

(a)LATENT HEAT OF FUSIONThe heat absorbed by melting solid

(b)LATENT HEAT OF VAPORISATIONThe heat absorbed during boiling

LATENT HEAT(hidden heat)

ABSORBS

Latent heat of fusion

Latent heat of vaporisation

RELEASES RELEASES

ABSORBS

FUSION (Melting)

SOLIDIFICATION (Freezes)

CONDENSATION (Condenses)

VAPORISATION (Boiling)

HEATING &COOLING CURVES

HOW TO CALCULATE?

Specific latent heat of fusion,lSPECIFIC LATENT HEAT OF FUSION, l is the

quantity of heat energy required to change 1kg solid to liquid at a constant temperature.

Q=heat energy,J m=mass,Kg l=specific latent heat

fusion,l P=power of electric,W t=heating time,s

SPECIFIC LATENT HEAT

If heat energy supplied by an electric immersion heater

Q=Pt #Pt=ml

SPECIFIC LATENT HEAT OF VAPORISATION,L

• Is defined as the quantity of heat energy required to change a 1 kg liquid to vapour at a constant temperature.

Q=mlif supplied by immersion heater,

Q=PtPt=ml

#When question involve change in temperature, Q=mc< #when

question involve change in phase,Q=ml#when involve both use, Q=mc< and Q=ml