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Ch.16 - Chemical Equilibrium
Tro - Chemistry: A Molecular Approach 5th Edition
Tro5th EditionChemistry: A Molecular ApproachISBN: 9780134874371Not the one you use?Change textbook
All textbooksTro 5th EditionCh.16 - Chemical EquilibriumProblem 34
Chapter 16, Problem 34

Find and fix the mistake in the equilibrium expression. PCl5(g) ⇌ PCl3(l) + Cl2(g) Kc = [Cl2]/[PCl5]

Verified step by step guidance
1
insert step 1> Identify the chemical reaction given: PCl5(g) ⇌ PCl3(l) + Cl2(g).
insert step 2> Recall that the equilibrium constant expression, Kc, is based on the concentrations of the gaseous and aqueous species involved in the reaction.
insert step 3> Note that PCl3 is in the liquid state, and pure liquids and solids do not appear in the equilibrium expression.
insert step 4> Write the correct equilibrium expression for the reaction: Kc = [Cl2]/[PCl5].
insert step 5> Verify that the expression only includes the gaseous species, which are Cl2 and PCl5.

Key Concepts

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

Equilibrium Expression

The equilibrium expression is a mathematical representation of the concentrations of reactants and products at equilibrium. It is derived from the balanced chemical equation and reflects the ratio of product concentrations to reactant concentrations, each raised to the power of their coefficients. For gaseous and aqueous species, concentrations are used, while solids and liquids are omitted from the expression.
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Equilibrium Constant Expressions

Phase of Substances in Equilibrium

In equilibrium expressions, only gases and aqueous solutions are included, while solids and liquids are excluded. This is because the concentration of pure solids and liquids does not change during the reaction and does not affect the equilibrium position. In the given reaction, PCl3 is a liquid, so it should not appear in the equilibrium expression.
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Phase Diagram Example

Correct Form of Kc

The correct form of the equilibrium constant Kc for the reaction PCl5(g) ⇌ PCl3(l) + Cl2(g) should only include the gaseous species. Therefore, the correct expression is Kc = [Cl2]/[PCl5]. The presence of PCl3 in the original expression is incorrect, as it is a liquid and should not be included in the equilibrium constant calculation.
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Kp vs Kc Relationship
Related Practice
Textbook Question

Consider the reaction: N2(g) + 3 H2(g) ⇌ 2 NH3(g) Complete the table. Assume that all concentrations are equilibrium concentrations in M.

T (K) [N2] [H2] [NH3] Kc

500 0.115 0.105 0.439 _

575 0.110 _ 0.128 9.6

775 0.120 0.140 _ 0.0584

Textbook Question

Consider the following reaction: H2(g) + I2(g) ⇌ 2 HI(g) Complete the table. Assume that all concentrations are equilibrium concentrations in M.

T (°C) [H2] [I2] [HI] Kc

25 0.0355 0.0388 0.922 _

340 _ 0.0455 0.387 9.6

445 0.0485 0.0468 _ 50.2

Textbook Question

Calculate Kp for each reaction.

b. N2(g) + 3 H2(g) ⇌ 2 NH3(g) Kc = 3.7⨉108 (at 298 K)

c. N2(g) + O2(g) ⇌ 2 NO(g) Kc = 4.10⨉10-31 (at 298 K)

Textbook Question

Consider the reaction: 2 NO(g) + Br2(g) ⇌ 2 NOBr(g) Kp = 28.4 at 298K In a reaction mixture at equilibrium, the partial pressure of NO is 108 torr and that of Br2 is 126 torr. What is the partial pressure of NOBr in this mixture?

Textbook Question

Calculate Kp for each reaction. a. N2O4(g) ⇌ 2 NO2(g) Kc = 5.9⨉10-3 (at 298 K)