If 2.0 mol nitrogen gas, 4.0 mol hydrogen gas, and 3.0 mol ammonia gas are added to a 20.0 L vessel and then heated to 500 K, what is the mass action expression? Will the system be at equilibrium? a) Kc = [NH₃]²/[N₂][H₂] Yes b) Kc = [NH₃]/[N₂][H₂] No c) Kc = [NH₃]²/[N₂]²[H₂] Yes d) Kc = [NH₃]/[N₂]²[H₂]²