change in its physical state
that occurs without changing its temperature.
The latent heat associatedwith melting a solid or freezing a liquid is called the heat
of fusion; that associatedwith vaporizinga liquid or a solid or condensing a vapour is
called the heat of vaporization.
The latent heat associatedwith melting a solid or freezing a liquid is called the heat
of fusion; that associatedwith vaporizinga liquid or a solid or condensing a vapour is
called the heat of vaporization.
The latent heat is normally expressed as the amount of heat (in units of joules or calories)
per mole or unit mass of the substance undergoing a change of state.
For example, when a pot of water is kept boiling, the temperature
remains at 100 °C (212 °F)
until the last drop evaporates, because all the heat being added to the
liquid is absorbed as
latent heat ofvaporization and carried away by the
escaping vapour molecules. Similarly,
while ice melts, it remains at 0 °C (32 °F), and the liquid water
that is formed with the latent
heat of fusion is also at 0 °C. The heat of fusion for water at 0
°C is approximately 334 joules
(80 calories) per gram, and the heat of vaporization at 100 °C is
about 2,260 joules
(540 calories) per gram. Because the heat of vaporization is so large,
steam carries a
great deal of thermal energy that is released when it condenses, making water
an excellent
working fluid for heat engines.
Watch this video to be more clear.
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