In reply to Michel Jullian's message of Sun, 4 Jun 2006 12:38:24 +0200: Hi, [snip] >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? :)))
According to:- >http://webbook.nist.gov/chemistry/form-ser.html.en-us.en delta Hgas = -241.826 kJ/mole and deltaHliquid = -285.830 kJ/mole. IOW both answers are correct, depending on whether the water forms as a vapor or as a liquid. As I understand it the difference is the heat of condensation + any heat derived from the cooling of the liquid. You need to look at the specific circumstances of any given experiment to determine which answer is "correct". In a car engine the water clearly forms as a vapor, and exits the engine as such. Unless waste heat is recovered from the exhaust, the energy of condensation is lost. Regards, Robin van Spaandonk http://users.bigpond.net.au/rvanspaa/ Competition provides the motivation, Cooperation provides the means.
