Latent Heat
Latent heat is the heat required to change a substance in
solid state into liquid or vapor or change liquid into vapor without change in
temperature.
Matter change from
one form to another, this is called change of state, the five sate of matter are solid, liquid , gas and
plasma and bose-estein condensates,
substance change from one of the following state to another, , in this process heat is either
absorbed or released by the substances. This process occur at the melting or
boiling point of the substances involved.
this heat is called the latent or hidden heat, because it does not show any change in the
temperature of the substance, at boiling or melting point of substances, the temperature does not change despite the
amount of heating, where those this heat go?
This heat went into breaking the inter-molecular force of attraction between
these substances to free the individual molecules that made up the substance.
Specific Heat Latent Heat
Specific latent heat is the quantity of heat required to
change 1kg mass of a substance from one state to another at constant
temperature.
There are two types of specific latent heat, specific latent
heat of fusion and specific latent heat of vaporization.
Latent heat of fusion
is the quantity of heat required to change a substance from solid state to
liquid state at melting point. This process occurs at the melting point of
substance or freezing point in case of ice. The temperatures remain the same
but the substance change from one state to another. Melting point is the
temperature at which a substance change from solid to liquid, freezing point is
the temperature at which liquid water change to solid ice. If there are impurities in a solid, it may
melt at temperature below its melting point; this is why salts are sprinkled on
snow to quick it melting.
Latent heat of vaporization is the quantity of heat required
to a substance from solid state to liquid state at boiling point. It occurs at
the boiling point of the liquid. Boiling point is the temperature at which the
saturated vapor pressure is equal to atmospheric pressure. If a substance does
not boil at the boiling point it means it is impure, impurities increases the boiling
point of most liquid.
Mathematically
If M is the mass of the substances,
Q is the amount of heat to cause the change.
L is latent heat. Then Q =ML
Determination Of
Specific Latent Heat Of Fusion
·
To determine the specific latent of fusion
of an ice follow the following procedure
·
put an ice into a well-lagged calorimeter hafly
filled with water
·
stir the water vigorously to ensure even
distribution of temperature
·
Note and record the initial and final temperature
of the calorimeter and content.
·
note heat loss by water and calorimeter = heat
required to melt the ice
To determine the specific latent heat of vaporization of
water follow the following steps
·
pass a
dry steam into the water in a
well-lagged calorimeter for some seconds,
·
Note and record the initial and final
temperature of the various mixture and their masses.
·
Note heat loss by steam = heat gained by water
and calorimeter.
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