: Michel Jullian wrote > > > Fred wrote: > >> So here is CHEMIX's thermochemistry answer for the reaction we discussed > >> (copy-paste): > >> > >> 2H2(g) + O2(g) = 2H2O(l) + 571.6kJ > >> > >> which solves the controversy (produced energy is equal to -dH=572kJ/mol, > > not > >> to -dG=474kJ/mol), doesn't it Fred? :))) > >> > > I'm not sure, Michel. The heat of formation from the elements dH is > > 2 x 498,000 for 2 H2 molecules from 4 H atoms and 498,000 for an O2 > > molecule > > from 2 O atoms. > > Then you have to break 3 x 498,000 = 1.49E6 kJ to form 2 H2Omolecules > > from 4 H atoms + 2 O atoms ---> H-O-H + H-O-H (4 x 498 kJ) - (3 x 498 kJ) > > = 498 kJ > > > > Which implies that 571.6 kJ - 498 kJ = 73.6 kJ is the heat given up > > by the two H2O molecules when cooled from a hot gas to liquid H2O > > in the calorimeter???. > > _Moles_ of atoms/molecules you mean Fred. Yes that's about it. Had you used > more accurate bond energies, instead of 73.6 kJ you would have found 88 kJ, > i.e. twice the water condensation energy 44kJ per mole of H2O (1 mole of H2O > = 18g = 6.02*10^23 molecules of H2O) > > Controversy solved? > Yes, but to show how the dH values vary check out this URL on Hess' Law.
http://wine1.sb.fsu.edu/chm1045/notes/Energy/HessLaw/Energy04.htm Fred > > Michel > >
