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March 27, 2017

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I'm doing chemical equilibrium, and there's a question in my lecture notes. Can someone check my answers and tell me if i'm right or wrong? Thanks!

The Kc expression for this reversible reaction:

3Fe(s) + 4H2O (g) --><-- Fe3O4(s) + 4H2 (g)


is [H2]^4 / [H2O]^4

Am I correct? My lecture notes apparently said that the reaction has a Kp expression but it didn't say anything about Kc expression. I just thought it can also have a Kc expression, not sure if i'm right.

  • Chemistry - ,

    And this one too! I thought it should also have a Kc expression but my notes only mentioned the Kp expression:
    ( that weird arrow is the forward backward arrow for a reversible reaction)



    H2(g) + Br2(l) --><-- 2HBr2(g)

    Kc = [HBr]^2 / [Br][H2]

    Please tell me if im right! I reasoned that there should be a Kc expression since for Kc expressions you should exclude water (when used as a solvent) and solids, so i thought that's applicable for these equations...

    please help thanks!

  • Chemistry - ,

    What is included in the Kp expression - partial pressures of the components.

    The partial pressure of a solid does not change, so does not appear in Kp. This is the same with Kc as solids do not appear in Kc.

    Liquids do not appear in Kp either.

  • Chemistry - ,

    Um. that does not answer my question of whether liquids, aqueous, and gases appear in Kc expressions or not.

  • Chemistry - ,

    OK

    Gases appear in Kc expressions as concentrations.

    In aqueous and other solvent systems the solute appears as a concentration in Kc expressions.

    Pure materials such as solids and solvents (including water) do not appear in the equilibrium expression.

    A substance such as water will of course appear if they are one of the products or reactants. For example in

    H2(g)+O2(g)<=> H2O(g)

    note the gas phase.

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