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Ch.7 Chemical Reactions: Energy, Rate and Equilibrium
McMurry - Fundamentals of General, Organic, and Biological Chemistry 8th Edition
McMurry8th EditionFundamentals of General, Organic, and Biological ChemistryISBN: 9780134015187Not the one you use?Change textbook
All textbooksMcMurry 8th EditionCh.7 Chemical Reactions: Energy, Rate and EquilibriumProblem 62a
Chapter 7, Problem 62a

For the following equilibria, use Le Châtelier's principle to predict the direction of the reaction when the pressure is increased by decreasing the volume of the equilibrium mixture.
a. C(s) + H2O(g) ⇌ CO(g) + H2(g)

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Identify the states of matter for each species in the equilibrium reaction: C(s) is a solid, H2O(g) is a gas, CO(g) is a gas, and H2(g) is a gas. Le Châtelier's principle primarily applies to gases when considering pressure changes.
Count the number of moles of gas on each side of the equilibrium. On the left side, there is 1 mole of gas (H2O(g)), and on the right side, there are 2 moles of gas (CO(g) and H2(g)).
Recall Le Châtelier's principle: When the pressure is increased (by decreasing the volume), the equilibrium will shift in the direction that reduces the total number of gas molecules to counteract the change.
Compare the number of gas molecules on each side. Since the left side has fewer gas molecules (1 mole) than the right side (2 moles), the equilibrium will shift toward the side with fewer gas molecules to reduce pressure.
Conclude that the reaction will shift to the left (toward the reactants) when the pressure is increased by decreasing the volume of the equilibrium mixture.

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Key Concepts

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

Le Châtelier's Principle

Le Châtelier's Principle states that if a dynamic equilibrium is disturbed by changing the conditions, the system will adjust itself to counteract that change and restore a new equilibrium. This principle is crucial for predicting how a reaction will respond to changes in concentration, temperature, or pressure.
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The following is an endothermic reaction where Kc = 6.73 x 103.For each of the choices below predict in which direction the reaction will proceed

Equilibrium and Reaction Quotient

In a chemical reaction at equilibrium, the rates of the forward and reverse reactions are equal, resulting in constant concentrations of reactants and products. The reaction quotient (Q) helps determine the direction in which the reaction will shift when conditions change, allowing us to predict how the system will respond to pressure changes.
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Chemical Equilibrium Concept 1

Effect of Pressure on Gaseous Reactions

In reactions involving gases, increasing the pressure by decreasing the volume favors the side of the equilibrium with fewer moles of gas. This is because the system will shift to reduce the pressure, thus understanding the mole ratio of gaseous reactants and products is essential for predicting the direction of the shift.
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Related Practice
Textbook Question

Oxygen can be converted into ozone by the action of lightning or electric sparks:

3 O2(g) ⇌ 2 O3(g)

For this reaction, ∆H = +69kcal/mol (+285 kj/mol) and K = 2.68 × 10-29 at 25 °C.

b. Are the reactants or the products favored at equilibrium?

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Textbook Question

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?

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Textbook Question

When the following equilibria are disturbed by increasing the pressure, does the concentration of reaction products increase, decrease, or remain the same?

a. 2 CO2(g) ⇌ 2 CO(g) + O2(g)

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Textbook Question

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

c. A catalyst is added?

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Textbook Question

Hydrogen chloride can be made from the reaction of chlorine and hydrogen:

Cl2(g) + H2(g) → 2 HCl(g)

For this reaction, K = 26 × 1033 and ∆H = -44 kcal/mol(-184 kJ/mol) at 25 °C.

a. Is the reaction endothermic or exothermic?

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Textbook Question

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

b. H2 is removed?

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