The reaction CO(g) + H2O(g) ⇌ CO2(g) + H2(g) has ∆H = -9.8 kcal/mol (-41 kJ/mol). Does the amount of H2 in an equilibrium mixture increase or decrease when the temperature is decreased?

Verified step by step guidance

1. Identify the type of reaction: The given reaction is exothermic because the enthalpy change (\( \Delta H \)) is negative, indicating that heat is released.
2. Apply Le Chatelier's Principle: In an exothermic reaction, decreasing the temperature shifts the equilibrium to the right, favoring the formation of products.
3. Determine the effect on \( \text{H}_2 \): Since the equilibrium shifts to the right, the concentration of \( \text{H}_2 \) will increase as more products are formed.
4. Consider the equilibrium expression: The equilibrium constant \( K_c \) is affected by temperature changes. For exothermic reactions, \( K_c \) increases as temperature decreases, further supporting the shift towards products.
5. Conclude the effect: Therefore, when the temperature is decreased, the amount of \( \text{H}_2 \) in the equilibrium mixture increases.

Key Concepts

Le Chatelier's Principle

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 temperature changes, if the temperature is decreased, the equilibrium will shift in the direction that produces heat, which can affect the concentrations of reactants and products.

Exothermic Reactions

An exothermic reaction is one that releases heat, indicated by a negative enthalpy change (∆H). In this reaction, since ∆H = -9.8 kcal/mol, it means that heat is released when CO and H2O react to form CO2 and H2. Understanding that this reaction is exothermic is crucial for predicting how temperature changes will affect the equilibrium position.

Equilibrium Constant (K)

The equilibrium constant (K) quantifies the ratio of concentrations of products to reactants at equilibrium for a given reaction at a specific temperature. Changes in temperature can alter the value of K, influencing the concentrations of H2 and other species in the reaction. For exothermic reactions, lowering the temperature typically increases K, favoring the formation of products.