For 2NO(g) + O₂(g) ⇌ 2NO₂(g), a mixture momentarily holds [NO] = 0.050 M, [O₂] = 0.20 M, and [NO₂] = 0.10 M. What is the value of Q?

Core Concept

Q copies the equilibrium expression: [NO₂]² divided by ([NO]²[O₂]). Substituting the snapshot values gives (0.10)² over ((0.050)² × 0.20). The numerator is 0.010 and the denominator is 0.0025 × 0.20 = 0.00050, so Q evaluates to 20. Exponents come from coefficients even though the mixture has not reached equilibrium.