1.
Temperature is a measure of the average kinetic energy of the
particles in a sample of matter. Although the kinetic energies of
individual molecules within a sample of matter may vary, the average
kinetic energy of the sample (and hence the temperature of the sample)
remains constant as long as no energy is added to or removed from the
sample. If two different samples of matter have the same temperature,
their particles have the same average kinetic energy. This is true even
if the two samples are of different kinds of matter and have different
masses.
2.
Heat is the name given to the energy that is transferred from one
object or sample of matter to another by virtue of a difference in their
temperatures. Whenever two samples of matter
having different temperatures come into contact, energy is spontaneously
transferred from the one of higher temperature to the one of lower
temperature until both samples have the same temperature.
3.
The amount of heat required to change the temperature of a sample of
matter by a certain amount depends on both the mass of the sample and
the kind of material of which the sample is made. Whenever
two samples of matter having different temperatures come into contact,
heat is spontaneously transferred from the one of higher temperature to
the one of lower temperature until both have the same temperature.
According to the Law of Heat Exchange, whenever two samples of matter
having different temperatures come into contact, the heat lost by the
sample that was initially at a higher temperature equals the heat gained
by the sample that was initially at a lower temperature. (The
temperature drop of the hotter sample, however, does not necessarily
equal the temperature gain of the cooler sample.)
4.
The physical state of a sample of matter can be changed by adding or
removing heat. Changing a sample of matter
from a solid to a liquid (melting) or from a liquid to a gas
(evaporation) is an endothermic process. Conversely, changing a sample
of matter from a gas to a liquid (condensation) or from a liquid to a
solid (freezing) is an exothermic process. A substance will boil, or
rapidly evaporate, when its vapor pressure is equal to the prevailing
atmospheric pressure. Even though heat is added to a liquid that is
boiling, the temperature of the liquid remains constant until all of the
liquid has changed to a gas (or vapor). Similarly, the temperature of a
substance remains constant as it melts (or freezes). The presence of
impurities in a liquid can raise its boiling point and lower its
freezing point.
