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Chemistry: Algebra Combining Equations [Enthalpy]

  1. Oct 22, 2005 #1
    Hi, I am stuck on this one question for a lab analysis I am doing. I missed the class where the teacher explained this and a lot more stuff. I also recall a question like this on a test I wrote on friday:rofl:

    Anyway here it is:

    Algebraically combine equations (2), (3), and (4) and their corresponding [Change in Enthalpy] values, to get (1) and [Change in Enthalpy] of combustion of magnesium.

    I just need to know how to do it, I can plug in the values after right?

    Let me know! thanks in advance!
  2. jcsd
  3. Oct 22, 2005 #2


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    Have you learnt about Hess's Law?
    "[URL [Broken]
    Your question requires a direct application of Hess's Law.
    Last edited by a moderator: May 2, 2017
  4. Oct 22, 2005 #3
    Ya I have learned Hess' law but I'm still unsure....

    So do I change the signs then add them together to get the enthalpy of equation 1?
    Last edited: Oct 23, 2005
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