Question

When 0.20 mol of hydrogen gas and 0.15 mol of iodine gas are heated at 723 K until equilibrium is established, the equilibrium mixture is found to contain 0.26 mol of hydrogen iodide.

The equation for the reaction is as follows.

H2(g) + I2(g) ↔ 2HI(g)

What is the equilibrium constant Kc of this reaction? Show the way with initial, react, and equilibrium mol.

Answer 1

Technically, one needs a volume since M is substituted into the Kc expression and not mols. You don't have a volume listed. However, the volume cancels as follows:
Kc = (mols HI/v)^2/(mols H2/v)(mols I2/v). That means we can assume any volume or ignore volume (or use 1 L)
(H2) initial = 0.2
(I2) initial = 0.15
(HI) equilibrium = 0.26

........H2 + I2 ==> 2HI
I......0.2..0.15......0
C......-x....-x......2x
E...0.2-x...0.15-x...2x
but you know 2x = 0.26 and that allows you to evaluate mols H2 and mols I2.

Substitute the E line into Kc expression and solve for Kc.

Post your work if you get stuck.