equilibrium constant (K)

value of the reaction quotient for a system at equilibrium; may be expressed using concentrations (K_c) or partial pressures (K_p)

when a reversible reaction has attained equilibrium at a given temperature, the reaction quotient remains constant

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Chemistry 2e · 13.2 Equilibrium Constants

Equilibrium Constants: practice problems

12 problems from the book, with its answers. Check your working, or have any of them explained to you on the whiteboard.

Exercises 7
Explain why an equilibrium between Br₂(l) and Br₂(g) would not be established if the container were not a closed vessel shown in Figure 13.4.
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Exercises 9
Among the solubility rules previously discussed is the statement: All chlorides are soluble except Hg₂Cl₂, AgCl, PbCl₂, and CuCl.
(a) Write the expression for the equilibrium constant for the reaction represented by the equation $AgCl (s) ⇌ Ag^{+} (a q) + Cl^{-} (a q) .$ Is K $_{c}$ > 1, < 1, or ≈ 1? Explain your answer.
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Exercises 11
Benzene is one of the compounds used as octane enhancers in unleaded gasoline. It is manufactured by the catalytic conversion of acetylene to benzene: $3 C_{2} H_{2} (g) ⇌ C_{6} H_{6} (g) .$ Which value of would make this reaction most useful commercially? ≈ 0.01, ≈ 1, or ≈ 10. Explain your answer.
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Exercises 13
For a titration to be effective, the reaction must be rapid and the yield of the reaction must essentially be 100%. Is K $_{c}$ > 1, < 1, or ≈ 1 for a titration reaction?
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Exercises 15
Write the mathematical expression for the reaction quotient, Q $_{c}$ , for each of the following reactions:
(a) $CH_{4} (g) + Cl_{2} (g) ⇌ CH_{3} Cl (g) + HCl (g)$
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Exercises 17
The initial concentrations or pressures of reactants and products are given for each of the following systems. Calculate the reaction quotient and determine the direction in which each system will proceed to reach equilibrium.
(a) $2 NH_{3} (g) ⇌ N_{2} (g) + 3 H_{2} (g) K_{c} = 17;$ [NH₃] = 0.20 , [N₂] = 1.00 , [H₂] = 1.00
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Exercises 19
The following reaction has K $_{P}$ = 4.50 $\times$ 10⁻⁵ at 720 K.
$N_{2} (g) + 3 H_{2} (g) ⇌ 2 NH_{3} (g)$
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Exercises 21
Which of the systems described in Exercise 13.15 are homogeneous equilibria? Which are heterogeneous equilibria?
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Exercises 23
For which of the reactions in Exercise 13.15 does K $_{c}$ (calculated using concentrations) equal K $_{P}$ (calculated using pressures)?
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Exercises 25
Convert the values of K $_{c}$ to values of K $_{P}$ or the values of K $_{P}$ to values of K $_{c}$ .
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Exercises 27
What is the value of the equilibrium constant expression for the change $H_{2} O (l) ⇌ H_{2} O (g)$ at 30 °C? (See Appendix E.)
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Exercises 29
Write the reaction quotient expression for the ionization of NH₃ in water.
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Key terms · 5

equilibrium constant (K): value of the reaction quotient for a system at equilibrium; may be expressed using concentrations (K_c) or partial pressures (K_p)
heterogeneous equilibria: equilibria in which reactants and products occupy two or more different phases
homogeneous equilibria: equilibria in which all reactants and products occupy the same phase
law of mass action: when a reversible reaction has attained equilibrium at a given temperature, the reaction quotient remains constant
reaction quotient (Q): mathematical function describing the relative amounts of reactants and products in a reaction mixture; may be expressed in terms of concentrations (Q_c) or pressures (Q_p)

Learn 13.2 on the whiteboard

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Read 13.2 in the textbook · This section on openstax.org

Equilibrium Constants: practice problems

12 problems from the book, with its answers. Check your working, or have any of them explained to you on the whiteboard.

Exercises 7

Explain why an equilibrium between Br₂(l) and Br₂(g) would not be established if the container were not a closed vessel shown in Figure 13.4.

Exercises 9

Among the solubility rules previously discussed is the statement: All chlorides are soluble except Hg₂Cl₂, AgCl, PbCl₂, and CuCl.

(a) Write the expression for the equilibrium constant for the reaction represented by the equation $AgCl (s) ⇌ Ag^{+} (a q) + Cl^{-} (a q) .$ Is K $_{c}$ > 1, < 1, or ≈ 1? Explain your answer.

Exercises 11

Benzene is one of the compounds used as octane enhancers in unleaded gasoline. It is manufactured by the catalytic conversion of acetylene to benzene: $3 C_{2} H_{2} (g) ⇌ C_{6} H_{6} (g) .$ Which value of would make this reaction most useful commercially? ≈ 0.01, ≈ 1, or ≈ 10. Explain your answer.

Exercises 13

For a titration to be effective, the reaction must be rapid and the yield of the reaction must essentially be 100%. Is K $_{c}$ > 1, < 1, or ≈ 1 for a titration reaction?

Exercises 15

Write the mathematical expression for the reaction quotient, Q $_{c}$ , for each of the following reactions:

(a) $CH_{4} (g) + Cl_{2} (g) ⇌ CH_{3} Cl (g) + HCl (g)$

Exercises 17

The initial concentrations or pressures of reactants and products are given for each of the following systems. Calculate the reaction quotient and determine the direction in which each system will proceed to reach equilibrium.

(a) $2 NH_{3} (g) ⇌ N_{2} (g) + 3 H_{2} (g) K_{c} = 17;$ [NH₃] = 0.20 , [N₂] = 1.00 , [H₂] = 1.00

Exercises 19

The following reaction has K $_{P}$ = 4.50 $\times$ 10⁻⁵ at 720 K.

$N_{2} (g) + 3 H_{2} (g) ⇌ 2 NH_{3} (g)$

Exercises 21

Which of the systems described in Exercise 13.15 are homogeneous equilibria? Which are heterogeneous equilibria?

Exercises 23

For which of the reactions in Exercise 13.15 does K $_{c}$ (calculated using concentrations) equal K $_{P}$ (calculated using pressures)?

Exercises 25

Convert the values of K $_{c}$ to values of K $_{P}$ or the values of K $_{P}$ to values of K $_{c}$ .

Exercises 27

What is the value of the equilibrium constant expression for the change $H_{2} O (l) ⇌ H_{2} O (g)$ at 30 °C? (See Appendix E.)

Exercises 29

Write the reaction quotient expression for the ionization of NH₃ in water.

Key terms · 5

equilibrium constant (K): value of the reaction quotient for a system at equilibrium; may be expressed using concentrations (K_c) or partial pressures (K_p)
heterogeneous equilibria: equilibria in which reactants and products occupy two or more different phases
homogeneous equilibria: equilibria in which all reactants and products occupy the same phase
law of mass action: when a reversible reaction has attained equilibrium at a given temperature, the reaction quotient remains constant
reaction quotient (Q): mathematical function describing the relative amounts of reactants and products in a reaction mixture; may be expressed in terms of concentrations (Q_c) or pressures (Q_p)

Learn 13.2 on the whiteboard

The tutor teaches the whole section, drawing it out step by step and answering your questions as you go.

Read 13.2 in the textbook · This section on openstax.org