[sweetdaisy186]

Given the following equilibrium, determine the value of K_c if the final concentration of CH₄ = 5.56 M, starting with [CH₄ = 4.00 M, [H2S = 8.00 M, [CS2 = 4.00 , and [H2] = 8.00 M.

The equation is CS₂ (g) + 4 H₂ --> CH₄ + 2H₂S (g) K_c=?

edit: to correct the spelling of 'equilibrium'

[sweetdaisy186]

I guess it would help if I gave my explaination right? LOL, sry

Anyways, I did the ICE table and came up with this

I       4                          8                   4                      8
C      -x                        -4x                 +X                    + 2x
E                                                       5.56

okay, so in the book they have in order of the chart from left to right 2.44, 1.76, 5.56, and 11.12 for E. I don't understand how you can calculate that answer because wouldn't 4+X=5.56 and give you an X of 1.56? So, then wouldn't you just take the 1.56 and add 2 to the last one, substract 4 from the second one and make the first one a -1.56? That is my theory, but since the book got a Kc of 29.40, I know that is wrong. I can calc. the Kc once I have the right E values, but I don't understand why my E values are wrong. Thanks!

[Donaldson Tan]

after u have solved for X, find the equilibrium concentration for all species, then proceed to evaluate Kc.

[sweetdaisy186]

That is what I have been doing, but I'm not getting the right answers. I am plugging in the 1.56 that I got for x into the ICE table and not getting the correct values. I don't understand why.  

[Donaldson Tan]

initially,
[CH4] = 4.00 M, [H2S] = 8.00 M, [CS2] = 4.00 , and [H2] = 8.00 M.

at equilibrium,
[CH4] = 5.56M
=> X = 5.56-4.00 = 1.56 (you r right that X = 1.56M)
[H2S] = 8.00 + 2X = 11.12M
[H2] = 8.00 - 4X = 1.76M
[CS2] = 4.00 - X = 2.44M

substituting the above values into the Kc expression, u get Kc = 29.366 ~ 29.4M^-2

you are correct. you ought to be more confident of yourself  :thmbup:

[sweetdaisy186]

Thanks for your *delete me* Yes, I do need more confidence in myself. This is something that I need to work on. *blushes* Thanks again!