The reaction H2(g) + I2(g) ⇌ 2 HI(g) has ∆H = -2.2 kcal/mol (-9.2 kJ/mol). Will the equilibrium concentration of HI increase or decrease when A catalyst is added?

Chemical equilibrium occurs when the rates of the forward and reverse reactions are equal, resulting in constant concentrations of reactants and products. In the given reaction, H2 and I2 combine to form HI, and the system can shift in response to changes in conditions, such as concentration, temperature, or pressure.

A catalyst is a substance that increases the rate of a chemical reaction without being consumed in the process. It works by lowering the activation energy required for the reaction to occur. Importantly, while catalysts speed up the attainment of equilibrium, they do not change the position of the equilibrium itself or the concentrations of reactants and products at equilibrium.

Le Chatelier's Principle states that if a dynamic equilibrium is disturbed by changing the conditions, the system will adjust to counteract the change and restore a new equilibrium. In the context of adding a catalyst, since it does not alter the concentrations of reactants or products, the equilibrium position remains unchanged, and thus the concentration of HI will not increase or decrease.