Pi = partial pressure and ni number of moles of component i.

Ideal gases obey Dalton’s law

(4)

For ideal gas mixture

                                                                                (5)

V is volume,  m is no of components, R is universal gas constant, n_i is number of moles of component iI and T is temperature p is partial pressure.

Thus for mixture of n component

                                                                                            (6)

Pt is total pressure as given by equation 4 and nt is total number of moles of gas in the mixture. The ratio between partial pressure and total pressure is

                                                                                           (7)

Here   is mole fraction of component in the mixture. The ratio between volume of a component with total volume at constant temperature and pressure is

Therefore for ideal gases volume percent equals mole percent.

Calculate the partial pressure of  and   on complete combustion of  with pure stoichiometric amount of oxygen.

   

 
  


  .


  atmoshpere


   atmosphere


 

Thus, in ideal gases partial pressure and volume fraction of a component is same.