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Which reaction will have a negative ∆H value

  1. Jul 4, 2016 #1

    TT0

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    1. The problem statement, all variables and given/known data
    Screen Shot 2016-07-04 at 2.14.39 PM.png
    2. Relevant equations


    3. The attempt at a solution
    Negative ∆H means that the product is more stable. Change from solid to gas requires energy so cancel out A and C. Reaction D doesn't make sense. The products of reaction B and E are more stable than the reactant because there is a full shell so it seems to me both would have a ∆H value. Can someone tell me what am I missing?

    Cheers!
     
  2. jcsd
  3. Jul 4, 2016 #2

    Borek

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    Staff: Mentor

    Reaction D does make a perfect sense.

    Ionization always requires energy.
     
  4. Jul 4, 2016 #3

    TT0

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    I thought chlorine didn't monatomic gases. So are you saying D is the answer? If so, why does it release energy?

    Thanks a lot
     
  5. Jul 4, 2016 #4

    Borek

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    Staff: Mentor

    Every diatomic molecule can be split (forced to dissociation) at temperatures high enough. It typically requires a lot of energy (hence the need for high temperatures).
     
  6. Jul 4, 2016 #5

    TT0

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    I see, so D has a positive ∆H value.

    Would you say both B and E have negative ∆H as the products are more stable?

    Cheers!
     
  7. Jul 4, 2016 #6

    Borek

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    Staff: Mentor

     
  8. Jul 4, 2016 #7

    TT0

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    So I guess A is the answer then? As it does not ionise. C is sublimation which requires energy. If A is the answer, isn't energy required for a particle to turn into a gas?

    Thanks!
     
  9. Jul 4, 2016 #8

    Borek

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    Staff: Mentor

    E is not ionization.
     
  10. Jul 4, 2016 #9

    TT0

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    I see. I got confused and forgot ionisation does not mean turning into an ion. Thanks a lot
     
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