Final answer:
The equilibrium constant expression for the reaction 2H₂(g) + S₂(g) → 2H₂S(g) is Keq = [H₂S]2 / ([H₂]2 × [S₂]), where the brackets indicate equilibrium concentrations of the gases in molarity.
Step-by-step explanation:
The equilibrium constant expression for a reaction system describes how the concentrations of reactants and products relate to each other when the reaction is at equilibrium. For the reaction 2H₂(g) + S₂(g) → 2H₂S(g), the equilibrium constant expression, Keq, can be written as:
Keq = [H₂S]2 / ([H₂]2 × [S₂])
In this expression, [H₂], [S₂], and [H₂S] represent the equilibrium concentrations of hydrogen, sulfur, and hydrogen sulfide gases, respectively. Given that the reaction takes place in a 1.00-liter vessel, the equilibrium constant can be directly related to the molarity of the gas species. In the scenario provided, you use the molarities 0.5 M for H₂, 0.02 M for S₂, and 68.5 M for H₂S.