For H₂(g) + I₂(g) ⇌ 2HI(g), K = 50 at some temperature. A vessel holds [H₂] = 0.10 M, [I₂] = 0.10 M, and [HI] = 0.50 M. Which way does the net reaction proceed?

Core Concept

Evaluating the quotient gives Q = (0.50)² ÷ (0.10 × 0.10) = 0.25 ÷ 0.010 = 25. Since 25 sits below K = 50, the mixture carries too little HI relative to equilibrium. The forward reaction runs fastest until enough HI accumulates to lift Q up to 50.