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Homework Help: Enthalpy change and activation energy

  1. Feb 21, 2008 #1
    Please can someone help.

    I am having trouble with the following question involving the production of nitric acid:

    What is the value for the enthaply change for reaction 2NO(g) + O2(g) 2NO2(g)

    and what is the activation energy for the forward reaction.

    I think the answer for the value of the enthalpy change is ΔH = -115 kJ mol-1 but am not sure.

    Could someone let me know if this is correct and help with the activation energy bit.


  2. jcsd
  3. Feb 21, 2008 #2
    Nitric acid?? Nitrogen dioxide.

    Your enthalpy for 2NO + O2 ---> 2NO2 looks plausible to me. This is a third order reaction and seems to involve a pre-equilibrium
    NO + O2 ---> NO3 followed by a collision of the latter with
    NO to form the nitrogen dioxide. The activation energy is reported as negative:
    E = -1.1 Kcal/mole (Benson, "The Foundations of Chemical Kinetics", McGraw-Hill, 1960) as
    measured by M. Bodenstein (Helv. Chim. Acta, 18, 743 (1935). Maybe this work is not the last word on this reaction, in which case you'll need to do some research in the library.
  4. Feb 22, 2008 #3
    [tex]2NO + O_2 --> 2NO_2[/tex]

    [tex]\Delta H^0_f (NO) = +\ 90.29\ kJ\ mol^{-1}:[/tex]

    [tex]\Delta H^0_f (NO_2) = +\ 33.10\ kJ\ mol^{-1}:[/tex]

    [tex]\Delta H^0_{reaction} = 2\cdot 33.10\ -\ 2\cdot 90.29 =\ -\ 114.38\ kJ\ mol^{-1}[/tex]
    Last edited: Feb 22, 2008
  5. Mar 7, 2008 #4
    the kinetic of the following reaction

    Hello, I am carrying a study on a column absorption of nitric acid, but I did not find the kinetic of the following reaction:
    2NO2 <-------> N2O4
    3NO2+H2O <----> 2HNO3+NO
    3HNO2+H2O <-----> ZABHNO3+2NO
    and 3HNO2+H2O <-----> HNO3+2NO
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