Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Chem - Equilibrium

  1. Mar 16, 2006 #1
    Reaction: [itex]CH_4 + 2H_2S <-> CS_2 + 4H_2[/itex]
    [itex]k_{eq} = 100[/itex] at a certain temperature

    An unkown amount of reactants were intorduced into a 1.0L bulb and at equilibrium 0.10 mol of [itex]CH_4[/itex] and 0.30 of [itex]H_2S[/itex] were found. Calc [itex]\[CS_2\][/itex] at equilibrium.

    I don't seem to have enough information here. I can form the equation for [itex]k_{eq}[/itex] but I have two unknowns...
    Last edited: Mar 16, 2006
  2. jcsd
  3. Mar 16, 2006 #2


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    Lousy problem statement: the idiot who wrote it mentally equates "reactants" with materials on "left-hand side of equation." Help?
  4. Mar 16, 2006 #3


    User Avatar

    Staff: Mentor

    Reactants or substrates? If reactants, there is no way to solve the question. If substrates, it is easy.

    Two unknowns - you mean amounts of CS2 and H2?

    Oops, Bystander was faster :)
  5. Mar 16, 2006 #4
    cscott I tried to resolve this. But before I show how I think this might be done, I want to make sure that I am right. Is the amount of [itex]\[CS_2\][/itex] at equilibrium 0.323 mol ?
  6. Mar 16, 2006 #5
    That idiot would be me :uhh:. Sorry.

    I've never heard of "substrates" before. We just barely learned that the reactions go both ways :tongue:, so I guess that's why I associated reactants with the LHS.


    I didn't get the answers for this practice sheet yet. Maybe you can show your method anyway?
    Last edited: Mar 16, 2006
  7. Mar 16, 2006 #6


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    Huh? You didn't write the problem, you're trying to solve it. All I was doing was translating what was meant by "reactants" as a hint for you.
  8. Mar 16, 2006 #7
    The problem originally stated the two molecules on the LHS instead of "reactants". I was just being lazy.

    I'm still not sure how to get the concentration of [itex]H_2[/itex] at equilibrium to in turn get it for [itex]CS_2[/itex]
  9. Mar 16, 2006 #8
    Ok. Here it goes.

    First, let's identify the initial amount of the various substances, reactants and products:
    CH4 -> n mol
    H2S -> m mol
    CS2 -> 0 mol
    H2 -> 0 mol

    At equilibrium according to the stoichiometric coefficients of the substances their amount should be:
    CH4 -> n - x mol
    H2S -> m - 2x mol
    CS2 -> x mol
    H2 -> 4x mol

    Nevertheless, the problem gives us the amount at equilibrium of CH4 and H2S which are respectively 0.10 mol and 0.30 mol.

    Then, we must apply the chemical equilibrium formula using the equilibrium constant given by the problem:

    100 = x(4x)^4) / (0.10 x 0.30^2)

    Now, it's math.
    x will be equal to 0.323 mol

    Hope I could help.
  10. Mar 16, 2006 #9
    Thanks PPonte.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook