Question

What is necessary for nitrogen in the air to combine with oxygen?

Answer 1

Hmmm, are you asking why we treat air as an homogeneous mixture?

Explanation:

`"Dalton's Law of Partial Pressure"` states that in a gaseous mixture, the pressure exerted by a component gas is the same the pressure it would exert if it alone occupied the container. And further that the total pressure is the SUM of the individual partial pressures.

Of course, in a gaseous mixture, the gaseous molecules are more or less independent of each other; they occupy a LARGE volume and are LOW DENSITY materials in comparison with the condensed phases.

In air, we can speak of the partial pressure of each component.

`P_"atmospheric"=P_(N_2)+P_(O_2)+P_"other gases"`

And using the Ideal Gas equation:

`1*atm=(RT)/V{n_(N_2)+n_(O_2)+n_("other gases")}`

Anyway, see here for similar treatment.