16-02-2013, 01:53 PM
Classical gas laws
Boyle's Law:
Boyle's law states that the volume V of a gas varies inversely with its pressure P . The equation below expresses Boyle's law mathematically:
PV = C
C is a constant unique to the temperature and mass of gas involved. plots pressure versus volume for a gas that obeys Boyles law
The subscripts 1 and 2 refer to two different sets of conditions. It is easiest to think of the above equation as a "before and after" equation. Initially the gas has volume and pressure V 1 and P 1 . After some event, the gas has volume and pressure V 2 and P 2.
Charles' Law:
Charles' law states that, at a constant pressure, the volume of a mixed amount of gas is directly proportional to its absolute temperature:
= k
Where k is a constant unique to the amount of gas and pressure. Just as with Boyle's law, Charles' law can be expressed in its more useful form:
=
The subscripts 1 and 2 refer to two different sets of conditions, just as with Boyle's law.
A plot of the temperature in Kelvin vs. volume gives :
Avogadro's Law:
Avogadro's law states that the volume of a gas at constant temperature and pressure is directly proportional to the number of moles of gas present. It's mathematical representation follows:
fracVn = k
k is a constant unique to the conditions of P and T . n is the number of moles of gas present.
1 mole (mol) of gas is defined as the amount of gas containing Avogadro's number of molecules. Avogadro's number ( N A ) is
N A = 6.022×1023
1 mol of any gas at 273 K (0_C) and 1 atm has a volume of 22.4 L. The conditions 273 K and 1 atm are the standard temperature and pressure (STP).