Ideal gas

From the experimental observations p-v-T behaviour of the gases given by,

pṽ = ṜT

Where Ṝ is the universal gas constant value of  Ṝ is 8.3141 J / mol K

ṽ is the molar specific volume m³/gmol

Dividing upper equation by the molecular weight µ.

pv = RT

Where v is specific weight m³/gmol

R is the characteristic gas constant

We also get this the equation in terms of total volume V of gas, 

PV = nṜT

PV = mRT

Where n is the number of moles and m is the mass of the gas. An equation can be written for two states of the gas is 

P₁V₁ / T₁ = P₂V₂ / T₂

All equation is called the ideal gas equation of state. At very low pressure or density, all gases and vapours approach ideal gas behaviour.