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Ch.15 - Chemical Equilibrium
All textbooksMcMurry 8th EditionCh.15 - Chemical EquilibriumProblem 126
Chapter 15, Problem 126

Methanol (CH3OH) is manufactured by the reaction of carbon monoxide with hydrogen in the presence of a Cu/ZnO/Al2O3 catalyst: CO(g) + 2H2(g) ⇌ CH3OH(g) ΔH° = -91 kJ. Does the amount of methanol increase, decrease, or remain the same when an equilibrium mixture of reactants and products is subjected to the following changes? (a) The temperature is increased. (b) CO is added. (c) Helium is added. (d) The catalyst is removed.

Verified step by step guidance
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Step 1: Consider the effect of temperature on the equilibrium. Since the reaction is exothermic (ΔH° = -91 kJ), increasing the temperature will shift the equilibrium to favor the endothermic direction, which is the reverse reaction. This will decrease the amount of methanol.
Step 2: Analyze the effect of adding CO. According to Le Chatelier's principle, adding more CO will shift the equilibrium to the right to counteract the change, increasing the amount of methanol produced.
Step 3: Evaluate the impact of adding helium. Adding an inert gas like helium at constant volume does not change the partial pressures of the reactants or products, so the equilibrium position remains unchanged, and the amount of methanol stays the same.
Step 4: Consider the role of the catalyst. Removing the catalyst will slow down the rate at which equilibrium is reached but does not affect the position of the equilibrium. Therefore, the amount of methanol at equilibrium remains the same.
Step 5: Summarize the effects: (a) Methanol decreases with increased temperature, (b) Methanol increases with added CO, (c) Methanol remains the same with added helium, (d) Methanol remains the same if the catalyst is removed.

Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Le Chatelier's Principle

Le Chatelier's Principle states that if a dynamic equilibrium is disturbed by changing the conditions, the position of equilibrium shifts to counteract the change. This principle helps predict how the concentration of reactants and products will change in response to alterations in temperature, pressure, or concentration.
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Le Chatelier's Principle

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 concentration or temperature can affect the value of K, thereby influencing the position of equilibrium and the amounts of reactants and products present.
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Catalysts and Reaction Rates

A catalyst is a substance that increases the rate of a chemical reaction without being consumed in the process. While catalysts speed up the attainment of equilibrium, they do not affect the position of equilibrium or the concentrations of reactants and products at equilibrium, as they influence both forward and reverse reactions equally.
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Related Practice
Textbook Question
Consider the exothermic reactionCoCl 2-1aq2 + 6 H O1l2 ∆ Co1H O2 2 + 1aq2 + 4 Cl-1aq2 which interconverts the blue CoCl 2- ion and the pinkCo 2 +CoCl 2- increase or decrease when the following changes occur?(c) The solution is diluted with water.
Textbook Question
The following reaction is important in gold mining: 4 Au1s2 + 8 CN-1aq2 + O21g2 + 2 H2O1l2 ∆ 4 Au1CN22-1aq2 + 4 OH-1aq2For a reaction mixture at equilibrium, in which direction would the reaction go to reestablish equilibrium after each of the following changes?(a) Adding gold