1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Thermochemistry - please help, test tomorrow

  1. Oct 26, 2004 #1
    [tex]N_2_{(g)} + \frac{5}{2}O_2 \longrightarrow N_2O_5 + \mathfrm 533 kJ energy[/tex]
    533kJ energy is released as heat

    We are given that 101.7g N2 , 102.97g O2 reacted. And this happens at T= 25C and P = 1atm

    what is the delta H and delta U for this process per mol N2(g). And how much work is done by the surrounding?

    Thanks
    (H<- enthalpy , U<- internal energy of the system )
    :confused:
     
    Last edited: Oct 26, 2004
  2. jcsd
  3. Oct 26, 2004 #2

    chem_tr

    User Avatar
    Science Advisor
    Gold Member

    First of all, you need to write the coefficients correctly for the reaction.

    [tex]N_2_{(g)} + \frac{5}{2}O_2 \longrightarrow N_2O_5 + \mathfrm 533 kJ energy[/tex]

    Then find the molar amounts of nitrogen and oxygen gas, by using N=14 and O=16 gram/mol.

    If a thermal energy is given to the environment, then it is an exothermic reaction, thus [itex]\Delta H[/itex] must be negative, and must have the dimension [tex]\frac {mol}{L}[/tex].

    I have no idea what [itex]\displaystyle \Delta U[/itex] is, so another friend will help you in the following days, I think.
     
    Last edited: Oct 26, 2004
  4. Oct 26, 2004 #3
    i found the number of moles for each gas, but we are not given the volume;As you say [itex]\Delta H[/itex] = [tex]\frac {mol}{L}[/tex]. And how is -533kJ usefull in this problem?
    Thanks
     
  5. Oct 26, 2004 #4
    H = U + pv, so therefore [tex]\Delta H = \Delta U + \Delta (pV)[/tex]. First off, what is [tex]\Delta U[/tex]?

    You can't find [tex]\Delta (pV)[/tex] directly. But for an ideal gas, what is pV equal to ?
     
    Last edited: Oct 26, 2004
  6. Oct 26, 2004 #5
    For an ideal gas: PV=nRT
    but how do I get U, (H=U+PV ) if i also need H
     
  7. Oct 26, 2004 #6
    I just realized something, you say the reaction occurs at 1 atm and 25 C, so it is both a constant temperature and constant pressure reaction ?
     
  8. Oct 27, 2004 #7
    1 mole of a gas = 24 L (24dm^3)

    So you have your mass, so just change that into number of moles, then multiply by 24 L. That will find your Volume.
     
  9. Oct 27, 2004 #8
    OK I don't know how you did on your test but

    1) For an isothermal reaction for an ideal gas, [tex]\Delta U = C_v\Delta T[/tex] and since presumably [tex]\Delta T = 0[/tex], it follows that [tex]\Delta U = 0 [/tex]

    2) Under constant pressure, [tex]\Delta H = q[/tex]. If you don't know what [tex]\Delta H[/tex] is, go back and look at the thermodynamics section in your first-year chemistry book.

    3) Well now since you know q and [tex]\Delta U[/tex] , you can solve for w, right ?
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Thermochemistry - please help, test tomorrow
  1. Blue lake test .HELP (Replies: 1)

Loading...