The equilibrium concentration?

Question

H2(g) + I2(g) ↔ 2HI Temperature = 731K


1.50 mol of H2 and 1.50 mol of I2 are placed in a 1.00 L vessel. What is the equilibrium concentration of HI in the gaseous mixture?
The equilibrium constant is K = 49.0

Answer 1

Let x moles of of the reactants react. Then at equilibrium, the concentrations of H2 and I2 are (1.5-x) and of HI = 2x.
Then [HI]^2/[H2][I2] = K
and then substitute, simplify, and solve the quadratic (dump the negative root).