6.8 General or Ideal Gas Equation
The General or Ideal Gas Equation is obtained by combining relations such as Boyle’s Law, Charles’ Law and Avogadro’s Law.
PV = nRT where
P Pressure
V  Volume
R  Constant
T  Temperature

This relation is referred to as ’Ideal gas Equation’ as it
holds good only when the gases are behaving as 'ideal' or perfect gases.
R can be calculated as follows :
We know that 1 mole of an ideal gas occupies 22.4 liter at S.T.P. (Standard Temperature & Pressure, i.e 1 atm. pressure and 273 K )
Units of Gas constant R
1) R = 0.082 liter atm deg^{1} mol^{1}
2) R = 8.31 ´ 10^{7} ergs deg^{1} mol^{1}
3) R = 8.31 J deg^{1} mol^{1}
4) R = 2 cal K^{1} mol^{1}
Finally at Glance
No. 
Gas Law 
Mathematical expression 
At constant 
1. 
Boyle’s 
P_{1}V_{1} = P_{2}V_{2} 
Temperature 
2. 
Charles 
V_{1}/ V_{2} = T_{1}/T_{2} 
Pressure 
3. 
PressureTemperature 
P_{1}/T_{1} = P_{2}/T_{2} 
Volume 
4. 
Graham’s 

Temperature
Pressure 
5. 
Gas equation 
PV = nRT 
 
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