Homework Help: Chemistry

Posted by Presh on Saturday, March 16, 2013 at 2:38pm.

A 5.00L reaction vessel is filled with 1.00mol of H2, 1.00mol of I2, and 2.50mol of HI. If equilibrium constant for the reaction is 129 at 500k, what are the equilibrium concentrations of all species?
H2(g) + I2(g) <-> 2HI(g) Kc = 129

Chemistry - DrBob222, Saturday, March 16, 2013 at 2:53pm
(H2) = 1.00/5.00 = 0.2M
(I2) = 1.00/5.00 = 0.2M
(HI) = 2.50/5.00 = 0.5M

.........H2 + I2 ==> 2HI
I........0.2...0.2...0.5
C........-x....-x....+2x
E.......0.2-x..0.2-x..0.5+2x

Kc = (0.5+2x)^2/(0.2-x)(0.2-x)

Note: In the C line, how do we know it is -x. -x, and +2x instead of +x +x, and -2x;i.e., how do we which way the reaction will occur. You run a Qrxn = (HI)^2/(H2)(I2)= (0.5)^2/(0.2)^2 = about 6. Compare with K = 129 and that means the numerator is too small and denominator is too large so the reaction must go to the right.
Chemistry - Presh, Saturday, March 16, 2013 at 5:56pm
What does x equal out too?

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