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Thread: Oxyhydrogen Calorific Value

  1. #1 Oxyhydrogen Calorific Value 
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    Can anyone point me to a reliable source for the calorific value of igniting Oxyhydrogen? I am looking for a figure in megajoules.Just trying to avoid all these incomplete and badly researched sites out there, I need to find a good source for this information if possible.Thanks and much obliged!


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  3. #2  
    Bullshit Intolerant PhDemon's Avatar
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    The figure you want is the enthalpy of combustion of hydrogen, under conditions of STP it is roughly -286 kJ/mol. You can calculate it at different temperatures using Kirchhoff's law (it does not depend on pressure).


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  4. #3  
    Brassica oleracea Strange's Avatar
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    According to Wikipedia: "241.8 kJ of energy (LHV) for every mole of H2 burned."
    Oxyhydrogen - Wikipedia, the free encyclopedia

    (I had never heard of oxyhydrogen before.)
    ei incumbit probatio qui dicit, non qui negat
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  5. #4  
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    Thanks - I had found that, not sure how reliable it is though. I need to convert it into Mj/L (megajoules per liter) and Mj/m3 (megajoules per meter cubed) - any tips....?

    Oxyhydrogen is a better term for the fuel economy virus better known as HHO or Browns Gas (there are some people out there ideas for applications, and apparently it works well with Diesel) but I however want it for a different purpose.
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  6. #5  
    Bullshit Intolerant PhDemon's Avatar
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    1 MJ =1000 kJ. As for the volume, if you know the temperature and pressure you can calculate the molar volume by assuming it is an ideal gas (usually a fairly good assumption) from PV=nRT, where P is the pressure, V the volume, n the number if moles, R is the gas constant and T is the temperature (make sure everything is in SI units though). If you use pressure in Pa, T in Kelvin and the gas constant in the correct units, V will be in m3, multiply this by 1000 to get the volume in litres. If memory serves one mole of gas at atmospheric pressure and 25 C has a volume of ~24 litres.
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  7. #6  
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    thanks PhDemon - thats a great help! One thing - where will I find the mass of one mole of Oxyhydrogen...?
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  8. #7  
    Bullshit Intolerant PhDemon's Avatar
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    As oxyhydrogen is a mixture the average molar mass will depend on the proportion of H2 and O2. The molar mass of H2 is 2, the molar mass of O2 is 32 so the molar mass of the mixture is (2 x mole fraction of H2) + (32 x mole fraction of O2) for a 2:1 (by moles or by volume) H2:O2 mixture it will be 12

    However, as the energy values you have been given are per mole of H2 burned you can calculate the energy output just by considering the mass of H2 burned, the molar mass of H2 is 2 as I said earlier.
    Last edited by PhDemon; June 19th, 2014 at 08:48 AM. Reason: corrected brain fart
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  9. #8  
    Brassica oleracea Strange's Avatar
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    Quote Originally Posted by PhDemon View Post
    so the molar mass of the mixture is (2 x mole fraction of H2) + (16 x mole fraction of O2) for a 2:1 (by moles or by volume) H2:O2 mixture it will be 666
    I see what you did there.
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  10. #9  
    Bullshit Intolerant PhDemon's Avatar
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    The brain fart has been corrected
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  11. #10  
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    Thanks for that! I will try to put something together and post back for peer review. Much obliged!
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