Question

At what temperature would you expect dinitrogen pentoxide to sublime?

N2O5(s)-->N2O5(g)

N2O5(s)= DELTA H -43.1
N2O5(s)= S (J*K1-*MOL1-)= 178.2

N2O5(g)= DELTA H 13.3
N2O5(g)= S (J*K1-*MOL1-)=355.7


where do i start here?

Answer 1

I believe it is done this way.
N2O5(s) ==> N2O5(g)
I assume the dH values are kJ/mol. Also I assume these are delta Hformation values.
dHrxn = (dH products) - (dH reactants)
dSrxn = (S products) - (S reactants). Remember to change S values to kJ.
Then dGrxn = dHrxn - TdSrxn
Finally, set dGrxn = 0 and solve for T (in kelvin). The answer is approximately 45 C.