[sparkly]

For this one I got a little farther. I converted the resulting grams of H2 to moles then divided by 2 because its a 2 liter vessel, and got .1415 for both H2 and Br2 And twice that for the HBr.
I just plugged those in to the Kc equation to get a Kc of 4. Am I on the right track?

A mixture of 1.374 grams of H2 and 70.31 grams of Br2 is heated in a 2.00 L vessel at 700 K. These substances react as follows:

H2(g) + Br2(g) <===> 2 HBr(g)

At equilibrium the vessel is found to contain 0.566 grams of H2.

(a) Calculate the equilibrium concentrations of H2, Br2, and HBr.

(b) calculate Kc.

[Las]

looks alright...I got 4 too..