For the reaction below, Kc = 0.154 at 2000 K.

Question

2 CH4(g) ⇌ C2H2(g) + 3 H2(g)

A 0.750 L equilibrium mixture at 2000 K contains 0.650 mol each of CH4(g) and H2(g).

What is the equilibrium concentration of C2H2(g)?

Answer 1

A 0.750 L equilibrium mixture at 2000 K contains 0.650 mol each of CH4(g) and H2(g).
(CH4) = (C2H2) = 0.650 mols/0.750 L = approx 0.9 but you need to use a more accurate number.
....................2 CH4(g) ⇌ C2H2(g) + 3 H2(g)
E....................0.9....................x..............0.9
Kc = (C2H2)(H2)^3/(CH4)^2
You know Kc, H2, and CH4, solve for C2H2