For the water–gas shift reaction CO1g2 + H2O1g2 ∆ CO21g2 + H21g2, ΔH° = - 41.2 kJ does the amount of H2 in an equilibrium mixture increase or decrease when the temperature is increased? How does Kc change when the temperature is decreased? Justify your answers using Le Châtelier's principle.

Key Concepts

Le Châtelier's Principle

Le Châtelier's Principle states that if a dynamic equilibrium is disturbed by changing the conditions, the position of equilibrium shifts to counteract the change. This means that if a system at equilibrium experiences a change in concentration, temperature, or pressure, the equilibrium will shift in a direction that minimizes the effect of that change.

Equilibrium Constant (Kc)

The equilibrium constant (Kc) is a numerical value that expresses the ratio of the concentrations of products to reactants at equilibrium for a given reaction at a specific temperature. Changes in temperature can affect the value of Kc; for exothermic reactions, increasing temperature typically decreases Kc, while decreasing temperature increases Kc, reflecting the shift in equilibrium position.

Exothermic Reactions

An exothermic reaction is a chemical reaction that releases heat, resulting in a negative change in enthalpy (ΔH). In the context of the water-gas shift reaction, the release of heat means that increasing the temperature will favor the reactants, leading to a decrease in the amount of H2 in the equilibrium mixture, while decreasing the temperature will favor the formation of products, increasing Kc.