Just when I thought I had done my chemestry homework for my column on water gas powered cars, I get blasted by someone that's obviously getting ready for a p-chem mid-term.
"Hey Jay,
I really liked the article you wrote about water gas, but I think you made a fairly big gaffe when you said "Hydrogen ... exist as a diatomic molecule with two atoms double bonded to each other in a pair like hydrogen ( H=H )..." because the Lewis structure for dihydrogen is ( H-H ). Natural hydrogen only has one electron( H. ), so two hydrogen can only form one bond( H. + .H -> H-H ) unless someone adds two extra electrons and some sort of outside pressure to keep it in this unnatural state.(unfilled outside octet).
I'm also a little confused about what you mean when you said, "The two atoms are now held together with two H-bonds making the molecule slightly harder to break apart and combust." Are you talking about water here or dihydrogen? If you're talking about water, the statement makes sense, but if you're talking about dihydrogen, that's just wrong. Dihydrogen has a low bond energy (432kJ/mol) compared to water (2*459kJ/mol), which is why it is such a good fuel. Even compared to a hydrocarbon (C-H=411kJ/mol), dihydrogen isn't that bad, it's just much more volatile (think Hindenburg).
Josh Silver
jsilver@eecs.berkeley.edu
PS: how do you go from calculating how much water you need per minute to run a 2 liter engine to screwing up lewis structures?"
Lewis Structures? It was a decade ago that I last heard that term, but if I'm not mistaken, it refers to how molecules are boned to each of its atomic components based on the number of free or valence electrons used in its bonding. I don't have my old notes, but the number of electrons involved significantly affect the bonding energy and distance between each atoms nucleus. But your not reading SCC's website for chemistry lessons. So I'll save the explination. Bottom line is I was wrong in my claim that Hydrogen gas (H-H) is double bonded. But the claim that a double bond takes more energy to break should be correct if it was indeed a double bond. What's more important though is the assertion that converting water to hydrogen for combustion is energetically inefficent. That part is still right.
So that makes the score engineering editor 0 : potential chemist 1. But just to make sure I have some legitimate grounds in making my claims, I posted my molecular calcuations for hydrogen combustion on this blog. Hopefully I did that homework right, especially considering I copied it from a chemistry professor friend of mine.
-JC <?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" /><o:p></o:p>