IDEAL GAS EQUATION

This is the combined gas equation of three laws and is known as ideal gas equation.

At constant T and n : V 1

P   Boyle’s law

At constant P and n : V T Charle’s law

At constant P and T : V n Avogadro law

Where R is proportionality constant known as universal gas constant.

Numerical value or R

R = 0.0821 litre atm K-1 mol-1

R = 0.0831 litre bar K-1 mol-1

R  = 8.314 J K-1mol-1

R = 1.987 ≈ 2 cal K-1 mol-1

R = 8.314 x 107 erg K-1 mol-1

If tempurature, volume and pressure of a fixed amount of gas vary from T1 , V1 and P1 to T2 , V2 and P2 then we can write,

This equation is also known as combined gas law.

• Dalton’s Law of Partial Pressure
When two or more non-reactive gases are enclosed in a vessel, the total pressure exerted by the gaseous mixture is equal to the sum of the partial pressure of individual gases.
Let P1 ,P2, and P3 be the pressure of three non reactive gases A, B, and C. When enclosed separately in the same volume and under same condition.
PTotal = P1+ P2 + P3
Where, PTotal = P is the total pressure exerted by the mixture of gases.

• Aqueous Tension
Pressure of non reacting gases are generally collected over water and therefore are moist. Pressure of dry gas can be calculated by substracting vapour pressure of water from total pressure of moist gas.
P2Dry gas = PTotal – Aqueous Tension

• Partial Pressure in terms of Mole Fraction
Let at the temperature T, three gases enclosed in the volume V, exert partial pressure P1 , Pand Prespectively, then

Where,    (n = n1 + n2 + n3)

                    P1 = n1 Ptotal