An experiment is conducted in which a quantity of H2(g) is chemically generated in a closed headspace of volume V1 at absolute temperature T1, thereby raising the total pressure from Pa (the initial air pressure) to Pf (the total final pressure of H2(g) + air).
Compose an algebraic expression for the volume (V2) that this sample of H2(g) would occupy if it were isolated (pure -- i.e. no air) at absolute temperature T2 and partial pressure P2.
Note that your expression may contain no other variables than those given above, namely: V1, T1, T2, Pa, Pf, and P2.