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?

Ch.7 Chemical Reactions: Energy, Rate and Equilibrium

McMurry - Fundamentals of General, Organic, and Biological Chemistry 8th Edition

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McMurry 8th Edition

Ch.7 Chemical Reactions: Energy, Rate and Equilibrium

문제 63

7장, 문제 63

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?

검증된 단계별 안내

Identify the type of reaction based on the given enthalpy change (∆H). Since ∆H = -9.8 kcal/mol, the reaction is exothermic, meaning it releases heat as a product.

Recall Le Châtelier's Principle, which states that if a system at equilibrium is subjected to a change in temperature, pressure, or concentration, the system will adjust to counteract that change and restore equilibrium.

Understand the effect of temperature on an exothermic reaction. Decreasing the temperature removes heat from the system. According to Le Châtelier's Principle, the equilibrium will shift to produce more heat, favoring the exothermic (forward) reaction.

Analyze the forward reaction: CO(g) + H2O(g) ⇌ CO2(g) + H2(g). Since the forward reaction produces H2 as a product, a shift toward the forward reaction will increase the amount of H2 in the equilibrium mixture.

Conclude that when the temperature is decreased, the equilibrium shifts toward the forward reaction, resulting in an increase in the amount of H2 in the equilibrium mixture.

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주요 개념

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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. Lowering the temperature favors the formation of products in exothermic reactions, as the system seeks to produce more heat.

Equilibrium Constant (K)

The equilibrium constant (K) 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 alter the value of K, influencing the position of equilibrium. For exothermic reactions, a decrease in temperature typically increases K, favoring the formation of products, including H2.