How can Gay-Lussac's law can be derived from the combined gas law?

1 Answer
Jul 24, 2017

If memory serves, that is the P/TPT relation, which is at constant volume and mols of gas.

We could start from the "combined gas law", but it came from the ideal gas law, so it would be simpler to start from the ideal gas law:

PV = nRTPV=nRT

Define the initial and final states, with constant VV and nn
(V_1 = V_2 -= VV1=V2V, n_1 = n_2 -= nn1=n2n):

P_1V = nRT_1P1V=nRT1 " "bb((1)) (1)

P_2V = nRT_2P2V=nRT2 " "bb((2)) (2)

By division,

((2))/((1)) = (P_2cancel(V))/(P_1cancel(V)) = (cancel(nR)T_2)/(cancel(nR)T_1)

Therefore,

P_2/P_1 = T_2/T_1

or

color(blue)(P_2/T_2 = P_1/T_1)

which is Gay-Lussac's Law.