Latent heat

• when heat is applied to a material the temperature of that material increases
• if the heat is removed and the material is allowed to cool then there is a decrease in that material’s temperature
• however when heat results in a change of state there will be no temperature change
• latent heat is the heat energy used to change to state of the material
• For example when a block of ice is heated no change in its temperature is observed during the period
• when it melts as the heat energy is used by the melting ice to change state
• when water changes into steam it absorbs heat energy and its temperature does not change
• when a substance changes state from solid to liquid and from liquid to gas it absorbs latent energy during the process
• latent heat of vapourisation-is the heat energy that is absorbed by a liquid as it changes into a vapour

Cooling curves

The cooling curve of naphthalene. Image credit MediaWiki

• When steam is cooled into condenses into a liquid
• If the liquid is cooled further it solidifies
• A cooling curve can be thus obtained
• This is a reverse of the heating curve
• As a vapour changes into a liquid it gives out heat which prevents a drop in temperature
• When the liquid solidifies the temperature remains the same while heat is given out

To access more topics go to the Combined Science Notes page.