Theory adiabatic
equation
Contrary to liquids and
solids, the volume of gases depends to a large extent on pressure and
temperature. The state of a gas is determined by volume, pressure, and
temperature. If one of these quantities is kept constant, there are simple
relations between the remaining two quantities. For constant volume (iso
volumetric change of state) we have GayLussac's law:
(1)
, V=const.
where p0 is
the pressure at 273.15 K, is
the coefficient of expansion, and t is the temperature in degrees
Centigrade. Extrapolating this law to low temperatures (t<0) we find that
there is an absolute zero point of our temperature scale, at which the
pressure is zero. This point is reached at 273.15°C. As all gases condense
before they reach this zero point, there will be deviations from equation
(1) at very low temperatures. So this law is valid only for ideal gases,
which by definition show no interaction between their molecules (
no condensation), and whose molecules can be considered as mass points (
no volume).
If you perform a change
of state in a gas while hindering any heat exchange with the surrounding
matter, compression will change both pressure and temperature. This process
is called an adiabatic one. In this case we have
(2)
(3)
where
is the ratio of the specific heat capacities at constant pressure, cp,
and at constant volume, cV:
= cp/cV
In German it is called
Adiabatenexponent and it depends on the number of atoms that form the
gas molecules.
http://de.wikipedia.org/wiki/Adiabatenexponent
http://en.wikipedia.org/wiki/Adiabatic_process
