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Calculating heat from H2 and O2

  1. Feb 9, 2009 #1
    It is known that Hydrogen and Oxygen when combined can combust of course. So my question is : Can I calculate the heat produced from this combustion if I put a certain amount of hydrogen and oxygen?

    Please Explain with an example.
  2. jcsd
  3. Feb 9, 2009 #2
    You certainly can calculate it. Since all H2/O2 molecules are identical, the same amount of energy will be released each time and so we can just quote a standard value from a textbook. I presume the reaction you have in mind is

    2*H2 + O2 --> 2*H2O

    which according to http://en.wikipedia.org/wiki/Hydrogen" [Broken] has an enthalpy of combustion equal to 287 KJ/mol.

    If you have a molar ratio different from 2:1 then complete combustion is impossible and the amount of energy you can extract will differ.
    Last edited by a moderator: May 4, 2017
  4. Feb 9, 2009 #3


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    Staff: Mentor

    Google "heat of combustion hydrogen", then multiply that number by the amount of hydrogen you have.
  5. Feb 10, 2009 #4
    I think I understand this part but I've got a couple of questions.

    1. When you say "complete combustion is impossible" that doesn't mean there's no combustion, there is but with a less or more amount. Right?

    2. if such thing (molar ratio diffrent than 2:1) happened how can I calculate the energy then.

    Again could you give me an example.

    Thanks alot.
  6. Feb 10, 2009 #5
    If I have the amount of hydrogen ( number of moles ) then I can calculate the heat energy. Ok, but let me get this right.. We didn't mention the oxygen because it doesn't have heat of combustion, but if I mix the hydrogen with any element that has heat of combustion I'll just add them to get the final heat of combustion. SO Is that right?
  7. Feb 10, 2009 #6
    Another Question :

    How can you calculate the temperature when you have the heat energy? I think of course it needs another factor like the "initial temprature" but I don't know...

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