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Ch.15 - Chemical Equilibrium
All textbooksBrown 15th EditionCh.15 - Chemical EquilibriumProblem 16b
Chapter 15, Problem 16b

Write the expressions for 𝐾𝑐 for the following reactions. In each case indicate whether the reaction is homogeneous or heterogeneous.
(b) Ti(𝑠) + 2Cl2(𝑔) β‡Œ TiCl4(𝑙)

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1
Identify the states of each reactant and product in the reaction: Ti(solid), Cl2(gas), and TiCl4(liquid).
Recognize that the reaction is heterogeneous because it involves reactants and products in different phases (solid, gas, and liquid).
Write the expression for the equilibrium constant, Kc, using the concentrations of the gaseous and aqueous species. Exclude solids and pure liquids from the expression.
For the reaction Ti(s) + 2Cl2(g) β‡Œ TiCl4(l), the expression for Kc is based only on the concentration of Cl2(g) since Ti(s) and TiCl4(l) do not appear in the expression.
The final expression for Kc is: Kc = 1/[Cl2]^2, where [Cl2] represents the concentration of chlorine gas.

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Key Concepts

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

Equilibrium Constant (Kc)

The equilibrium constant, Kc, 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. It is calculated using the formula Kc = [products]^[coefficients] / [reactants]^[coefficients]. Understanding Kc is essential for predicting the direction of a reaction and the extent to which reactants are converted to products.
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Homogeneous vs. Heterogeneous Reactions

Homogeneous reactions occur when all reactants and products are in the same phase (solid, liquid, or gas), while heterogeneous reactions involve reactants and products in different phases. This distinction is important because it affects how concentrations are expressed in the Kc expression. For example, in a heterogeneous reaction, solids and liquids are not included in the Kc expression, as their activities are considered constant.
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Phase Representation in Kc Expressions

In Kc expressions, only the concentrations of gaseous and aqueous species are included, while pure solids and liquids are omitted. This is because the concentration of pure substances does not change during the reaction. For the given reaction, Ti(s) is a solid and TiCl4(l) is a liquid, so they will not appear in the Kc expression, which will only include the gaseous reactants.
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Related Practice
Textbook Question

The equilibrium constant for the dissociation of molecular iodine, I2(g) β‡Œ 2 I(g), at 800 K is Kc = 3.1Γ—10βˆ’5. (b) Assuming both forward and reverse reactions are elementary reactions, which reaction has the larger rate constant, the forward or the reverse reaction?

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Textbook Question

Write the expression for Kc for the following reactions. In each case indicate whether the reaction is homogeneous or heterogeneous.

(a) 3 NO(g) β‡Œ N2O(g) + NO2(g)

(b) CH4(g) + 2 H2S(g) β‡Œ CS2(g) + 4 H2(g)

(c) Ni(CO)4(g) β‡Œ Ni(s) + 4 CO(g)

(d) HF(aq) β‡Œ H+(aq) + F-(aq)  

(e) 2Ag(s) + Zn2+(aq) β‡Œ 2 Ag+(aq) + Zn(s)

(f) H2O(l) β‡Œ H+(aq) + OH-(aq)

(g) 2 H2O(l) β‡Œ 2 H+(aq) + 2 OH-(aq)

Textbook Question

Write the expressions for Kc for the following reactions. In each case indicate whether the reaction is homogeneous or heterogeneous.

(a) 2 O3(g) β‡Œ 3 O2(g)

(c) 2 C2H4(g) + 2 H2O(g) β‡Œ 2 C2H6(g) + O2(g)

(d) C(s) + 2 H2(g) β‡Œ CH4(g)

(e) 4 HCl(aq) + O2(g) β‡Œ 2 H2O(l) + 2 Cl2(g)

(f) 2 C8H18(l) + 25 O2(g) β‡Œ 16 CO2(g) + 18 H2O(g)

(g) 2 C8H18(l) + 25 O2(g) β‡Œ 16 CO2(g) + 18 H2O(l)

Textbook Question

Which of the following reactions lies to the right, favoring the formation of products, and which lies to the left, favoring the formation of reactants?

(a) 2 NO(g) + O2(g) β‡Œ 2 NO2(g) Kp = 5.0 Γ— 1012

(b) 2 HBr(g) β‡Œ H2(g) + Br2(g) Kc = 5.8Γ—10βˆ’18