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Homework Help: Help with enthalpy

  1. Feb 22, 2008 #1
    I am not sure how to find this... estimate the energy change that occurs when carbon monoxide and chlorine combine to make phosgene....

    CO(g) + Cl2(g) ---> Cl2CO(g)

    i have an idea of what to do,except i think its not the right way.
  2. jcsd
  3. Feb 22, 2008 #2
    They do not give enthalpies of formation or Bond dissociation energies?
  4. Feb 22, 2008 #3
    Maybe you want to have a look to the thread " Enthalpy change and activation energy".
  5. Feb 22, 2008 #4
    claudzterz9, you can do that by reacting CO and Cl2 in a calorimeter, by measuring temperatures before and after reaction.
  6. Feb 22, 2008 #5
    take the bond energy values from your data booklet....
  7. Feb 23, 2008 #6
    If your problem is to estimate it from given bond energies, as Kushal wrote, then in the reaction

    CO(g) + Cl2(g) ---> COCl2(g)

    1. You go from a triple bond in CO to a double bond between C and O in COCl2; so you have to compute this difference of energy.
    2. You loose a Cl-Cl bond and you gain 2 C-Cl bonds

    So, calling E1 the energy of the triple bond between C and O, E2 the energy of double bond between C and O in phosgene, E3 the bond energy Cl-Cl and E4 the bond energy C-Cl, you have, as estimated reaction energy:

    E2 - E1 + 2E4 - E3 ~ 128 kJ/mol with the data I've found (but remember there is quite variation on these kind of data).

    Edit. The reaction enthalpy is the same but with sign changed.
    Last edited: Feb 23, 2008
  8. Feb 25, 2008 #7
    the answer u r looking for is -100 KJ/mol..........

    how i got it is by lookin at the avg bond energies for the reactants and the sum for that is 1310 and then i lloked for the the sum of the avg bond energies for the product whih is 1410.....

    subtract the 2 and you get -100 kj/mol
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