Michel Jullian wrote: > > BTW Fred, have you given some thought to our enthalpy vs Gibbs controversy? > Which energy can be recovered from the reaction below do you think, the > enthalpy change or the Gibbs free energy change? > Is that a trick question, Michel?
The H-H bond is 498 Kjoule/mole the same as the O-O bond and the O-H bond.. Hence overall, H-H + O-O ----> H-O-H + O nets Zip Gibbs or Enthalpy. But, O + Fe ---> Fe-O: Fe-O (390 KJ/mole) minus Fe-Fe (100 KJ/Mole) equals a Gibbs Free Energy of 390-100 = 290 KJ when you oxidize iron with O radicals. :-) OTOH, H-O-H 2 x 498 KJ/Mole + Ni ----> NiO (382 KJ/mole) + H-H = 498 - 382 = 116 KJ/mole. Easy to Compare Enthalpy with the Ellingham (enthalpy) Diagrams. http://www.chem.mtu.edu/skkawatr/Ellingham.pdf Fred. > > Michel > > ----- Original Message ----- > From: "Frederick Sparber" <[EMAIL PROTECTED]> > To: "vortex-l" <[email protected]> > Sent: Friday, June 02, 2006 4:52 PM > Subject: Re: Free Radical Chain Reactions > > > > Actually 2 H2 + O2 ----> 2 H2O has about 14 reaction steps. > > > > http://www.cheresources.com/reactionkinetics3.shtml > > > > "Another important consideration is the formation of chain reactions. The > > basic premise of chain reaction mechanisms is also that free radicals play > > a leading role in the destruction of reactant molecules. The chain > > reaction mechanism itself consists of several steps: initiation, > > propagation, branching (not always present), and termination. This can be > > illustrated, for certain range of temperature and pressure, by some of the > > reactions in the following Hydrogen oxidation mechanism:" > > > > "To summarize, reaction mechanisms can be assembled from elementary > > reactions using free radicals as the means for decomposition of the > > reactant, and intermediate products. Chain branching reactions, if they > > occur, take a very important role in the mechanism as they lead to the > > formation of increasing concentrations of radicals. Reaction time and > > temperature have a bearing on radical concentration, and the type of > > reaction initiating the consumption of the reactant" >
