Since PbO to Pb+(1/2)O2 releases 217.3kJ and CO to C+(1/2)O2 releases 110.5kJ, what I think is that PbO+CO to Pb+(1/2)O2+C+(1/2)O2 releases 327.8kJ. Now, the book says PbO+CO to Pb+C+O2 releases 327.8kJ.

My question is, why does is there no energy involved making Pb+(1/2)O2+C+(1/2)O2 into Pb+C+O2? Wouldn't there be some energy released joining the two halfs of oxygen?

  • $\begingroup$ why did the O become (1/2)O2? $\endgroup$
    – 12345bird
    May 13, 2020 at 10:18
  • 3
    $\begingroup$ It's like how half a dozen eggs + half a dozen eggs = one dozen eggs. It's not a dozen of half-eggs (that would be a tragedy!). $\endgroup$ May 13, 2020 at 18:03
  • $\begingroup$ oh ok, thanks! thats a funny analogy! $\endgroup$
    – 12345bird
    May 14, 2020 at 16:51

1 Answer 1


There are no two halfs of oxygen. The half denotes that there is $\frac{1}{2}$ a mole of oxygen produced for every mole of $\ce{PbO}$ (or $\ce{CO}$) reacting. So there is no such "joining of oxygen halves" going on.

  • $\begingroup$ ok thanks, I get it! the 1/2 is just a simplification so we dont have to multiply everything by 2. $\endgroup$
    – 12345bird
    May 14, 2020 at 16:52

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