| HOW DOES FREEZING RELEASE HEAT ENERGY?
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METEOROLOGIST JEFF HABY
When water is freezing it makes sense to think that the water is getting colder. When you think
of the word freezing you think of it being cold. Actually, when
water freezes it stays at a constant temperature. That constant temperature is the freezing
point of 32 F (0 C). Suppose you have a small cup of water that has a temperature of 50 F. You
place that cup of water outside where the temperature is 20 F. There is also a thermometer
in the water to record the temperature. When the water is placed outside the temperature
of the water will gradually cool. The thermometer will start at 50 F and it will gradually cool.
Once the temperature reaches 32 F the temperature will stop cooling. At that point the liquid
will begin to turn to ice. During the entire time the liquid is converting to ice the
temperature will stay at a constant of 32 F. Once all the liquid is frozen then the temperature
will resume the decrease. The temperature of the ice will continue to decrease until it
reaches the same temperature as the outside air which is 20 F.
Liquid water has more energy than frozen water. When water freezes it gives up some of
the water's energy. This energy that is given up is the
latent heat of freezing. When the
water was freezing latent heat of freezing energy was being released. Heat energy was
actually being released. It is this heat energy that prevented the temperature from
continuing to cool once the temperature reached 32 F. The way to think of this is that
the heat energy does not warm the temperature but rather stops the cooling. The cooling
that would have occurred is perfectly offset by the latent heat energy release and thus
the temperature remains constant. When a latent
heat process occurs the temperature remains constant. Energy is being transferred even
through the temperature is constant. A mixture of water and ice will always have
an equilibrium temperature of 32 F. Only when it is only liquid or only ice will the
temperature increase or decrease.
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