Textbook Question
The equilibrium constant for the dissociation of molecular iodine, I2(g) ⇌ 2 I(g), at 800 K is Kc = 3.1 × 10–5. (a) Which species predominates at equilibrium I2 or I?
Ch.15 - Chemical Equilibrium
Chapter 15, Problem 16a,c,d,e,f,g
Write the expressions for Kc for the following reactions. In each case indicate whether the reaction is homogeneous or heterogeneous.
(a) 2 O3(g) ⇌ 3 O2(g)
(c) 2 C2H4(g) + 2 H2O(g) ⇌ 2 C2H6(g) + O2(g)
(d) C(s) + 2 H2(g) ⇌ CH4(g)
(e) 4 HCl(aq) + O2(g) ⇌ 2 H2O(l) + 2 Cl2(g)
(f) 2 C8H18(l) + 25 O2(g) ⇌ 16 CO2(g) + 18 H2O(g)
(g) 2 C8H18(l) + 25 O2(g) ⇌ 16 CO2(g) + 18 H2O(l)
Verified step by step guidance1
Step 1: Identify the phases of each component in the reaction. The reaction given is: 2 C_8H_18(l) + 25 O_2(g) ⇌ 16 CO_2(g) + 18 H_2O(l). Here, C_8H_18 and H_2O are in the liquid phase, while O_2 and CO_2 are in the gaseous phase.
Step 2: Determine if the reaction is homogeneous or heterogeneous. A homogeneous reaction involves reactants and products in the same phase, while a heterogeneous reaction involves different phases. Since this reaction involves both gases and liquids, it is a heterogeneous reaction.
Step 3: Write the expression for the equilibrium constant K_c. For heterogeneous reactions, only the concentrations of gases are included in the K_c expression. Therefore, K_c = [CO_2]^{16} / [O_2]^{25}.
Step 4: Note that the concentrations of pure liquids and solids are not included in the K_c expression because their activities are considered to be 1.
Step 5: Ensure the expression is balanced according to the stoichiometry of the reaction. The exponents in the K_c expression correspond to the coefficients of the gaseous species in the balanced chemical equation.>
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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 the concentrations of 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 into products.
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Equilibrium Constant Expressions
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 concentrations do not change significantly.
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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 activity of pure solids and liquids is considered to be constant. Understanding how to represent different phases in Kc expressions is crucial for accurately writing the equilibrium constant for a given reaction, as seen in the provided reaction involving liquid and gaseous components.
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02:06Kp vs. Kc Formula
Related Practice
Textbook Question
The equilibrium constant for the dissociation of molecular iodine, I2(g) ⇌ 2 I(g), at 800 K is Kc = 3.1×10−5. (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) ⇌ N2O(g) + NO2(g)
(b) CH4(g) + 2 H2S(g) ⇌ CS2(g) + 4 H2(g)
(c) Ni(CO)4(g) ⇌ Ni(s) + 4 CO(g)
(d) HF(aq) ⇌ H+(aq) + F-(aq)
(e) 2Ag(s) + Zn2+(aq) ⇌ 2 Ag+(aq) + Zn(s)
(f) H2O(l) ⇌ H+(aq) + OH-(aq)
(g) 2 H2O(l) ⇌ 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.
(b) Ti(𝑠) + 2Cl2(𝑔) ⇌ TiCl4(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) ⇌ 2 NO2(g) Kp = 5.0 × 1012
(b) 2 HBr(g) ⇌ H2(g) + Br2(g) Kc = 5.8×10−18