Fred I really meant "the reaction below", H2 combustion in O2: 2 H2 + O2 ----> 2 H2O
How many joules per mole does this produce, and does this correspond to the enthalpy change or to the Gibbs free energy change of the reaction? The question is only intended to solve the controversy one way or another, I haven't looked up the answer. Admittedly I have my own opinion of what it will be (enthalpy), so in this sense you can call it a trick question. Michel ----- Original Message ----- From: "Frederick Sparber" <[EMAIL PROTECTED]> To: <vortex-l@eskimo.com> Sent: Saturday, June 03, 2006 3:53 PM Subject: Re: Free Radical Chain Reactions > 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" <vortex-l@eskimo.com> >> 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" >> > > >
