1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

[CHEM] Equlibrium Help !

  1. Nov 16, 2005 #1
    [CHEM] Equlibrium Help plz!

    Hi, I am having trouble with a few questions on my chapter review and I have a test tomorrow. I wasn't at school today so I didn't get the chance to ask questions.

    1. The oxidation of sulfur dioxide to sulfur trioxide is an important reaction. At 1000K, the value of Kc is 3.6x10^-3.
    2 SO2 + O2 <-> 2 SO3
    A closed flask originally contains 1.7 mol/L SO2 and 1.7 mol/L O2. What is [SO3] at equilibrium when the reaction vessel is maintained at 1000K?
    Ok So I set up the ice table and for equilbrium i get 1.7-2x [SO2], 1.7-2x [O2], and 2x for [SO3]. Then...

    Kc = -____[SO3]^2____
    3.6x10^-3 = ____(2x)^2____
    ------------(1.7-2x)^2 (1.7-x)
    (3.6x10^-3)(2.89-6.8x-4x^2)(1.7-x) = 4x^2
    (3.6x10^-3)(4.913-14.45x+13.6x^2-4x^3)= 4x^2

    I didn't go any further because I don't know what to do now that there is an x cubed. Unless I'm doing it wrong, could you please correct me.

    2. Write the chemical equation for the reversible reaction that has the following equilibrium expression.
    Kc = blah blah blah
    Now, the eqn would be: 4 NH3 + 5 O2 <-> 4 NO + 6 H2O
    Assume that, at a certain temperature, [NO] and [NH3] are equal. Also assume that [H2O] = 2.0 mol/L and [O2] = 3.0 mol/L. What is the value of Kc at this temperature.

    What do I do for this question?
    Last edited: Nov 16, 2005
  2. jcsd
  3. Nov 16, 2005 #2

    Physics Monkey

    User Avatar
    Science Advisor
    Homework Helper

    The equation is cubic and would generally be solved numerically (though a nasty formula, analogous to quadratic formula, does exist for cubic polynomials). There are ways to find a good approximate answer which is still correct to several decimal places.

    What would you naively expect the value of x to be? In other words, will x be large (close to 1.7 say), will x be small (near zero), or something more in the middle? To rephrase it one more way, do you expect a lot or a little S03 to be produced?
    Last edited: Nov 16, 2005
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?

Similar Discussions: [CHEM] Equlibrium Help !
  1. Chem Help! (Replies: 2)

  2. Help with Chem ? (Replies: 1)

  3. Stuck on chem hw HELP (Replies: 7)

  4. Chem help! (Replies: 1)