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Homework Help: Chemical equation; reaction; balancing problem.

  1. Sep 21, 2009 #1
    1. The problem statement, all variables and given/known data

    All of a sample of Mg(OH)2 was converted to Mg3N2 by:

    Mg3N2 -> Mg(OH)2

    Give the mole ration of Mg(OH)2 to Mg3N2 in that reaction.

    3. The attempt at a solution

    Well I'm having trouble just making heads or tails of the equation in the first place. Should I sart balancing by adding the missing elements/ions, ie, the N2, and OH-?
    1. The problem statement, all variables and given/known data

    2. Relevant equations

    3. The attempt at a solution
  2. jcsd
  3. Sep 21, 2009 #2


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    Gold Member

    1] 3Mg(OH)2+2NH3=Mg3N2+6H2O

    2] 3Mg(OH)2+N2O=Mg3N2+3H2O+2O2

    the first is more appropriate [not sure if it's possible to have oxygen gas as a product of a chemical reaction]
  4. Sep 22, 2009 #3


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    Staff: Mentor

    You don't have to balance any reaction - number of moles of Mg doesn't change, so it will be always 3 moles of Mg(OH)2 giving one mole of Mg3N2.

    Such approach is quite effective and fast when you do stoichiometric questions - there is no need to waste time on balancing other elements, when you can predict molar ratio of reagent and substrate just from formulas and mass conservation.

  5. Sep 23, 2009 #4
    Thanks guys.
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