
Boiling water. Image credit chemistryland.com
ZIMSEC O Level Combined Science Notes: 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.
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