Final answer:
The forward equilibrium expression for aA + bB ↔ cC + dD is Kc = [C]^c × [D]^d / ([A]^a × [B]^b), and the reverse expression is the reciprocal of the forward expression. For gaseous reactions, partial pressures are used in place of concentrations to formulate the equilibrium expressions Kp.
Step-by-step explanation:
The forward and reverse equilibrium expressions for the chemical reaction aA + bB ↔ cC + dD are important for understanding dynamic equilibrium in chemistry. The forward equilibrium expression, also known as the equilibrium constant expression (Kc), for this reaction would be Kc = [C]^c × [D]^d / ([A]^a × [B]^b), where square brackets represent the concentration of each substance. Conversely, the reverse equilibrium expression is the reciprocal of the forward expression, which is Kc = 1 / ([C]^c × [D]^d / ([A]^a × [B]^b)).
When considering reactions involving gases, the equilibrium expressions use partial pressures instead of concentrations. Thus, the forward expression would be Kp = (PC)^c × (PD)^d / ((PA)^a × (PB)^b), and the reverse would be Kp = 1 / ((PC)^c × (PD)^d / ((PA)^a × (PB)^b)).
Dynamic equilibrium is reached when the rates of the forward and reverse reactions are equal, resulting in no net change in concentrations of reactants and products, although the reactions continue to occur in both directions.