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In 1802, Joseph Guy-Lussac experimented with the relationships between pressure and
temperature and came up with an equation a lot like Charles’s Law:
P/T = Constant.
Generalized Gas Law — We can combine Boyle’s, Charles’s and Gay-Lussac’s laws to
express this generalized gas law:
PV/T = Constant
Where the value of the constant depends on the amount of gas present and T is the
absolute (or Kelvin) temperature.
Ideal Gas Law — The Generalized Gas Law can be written in a slightly different man-
ner:
PV = nRT
When written this way, it is called the Ideal-Gas Law. R is the gas constant and n is
the number of moles of gas. The gas constant can be examined experimentally as R
= 0.082 liter atm/Kelvin moles. Knowing R, the fourth variable can be evaluated if any
three are known.
The gas laws are valid for most gases at moderate temperatures and pressures. At
low temperatures and high pressures, gases deviate from the above laws because the
molecules are moving slowly at low temperatures and they are closer together on the
average at higher pressures.
Ideal vs. Real Gas — Gases are typied as ideal or real. The ideal gas follows certain
gas laws exactly; whereas, a real gas closely follows these laws only at low density.
Ideal behavior can be ascribed to a real gas, if its molecules are separated by very large
distances; so that intermolecular attraction is negligible.
Adiabatic Process (ad-ee-uh-bat-ik) — Adiabatic compression and expansion are
thermodynamic processes in which the pressure of a gas is increased or decreased
without any exchange of heat energy with the surroundings. Any process that occurs
without heat transfer is called an adiabatic process.
The adiabatic compression, or expansion of a gas, can occur if the gas is insulated from
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