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CHEM H2C (3)
Chapter 16

CHEM H2C Chapter 16: Chemical Equilibrium

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University of California - Irvine

Ch.16:ChemicalEquilibrium Textbook: Chemistry Structure and Properties by Nivaldo J. Tro *pictures and definitions from textbook • Thermodynamics: extent of a chemical reaction • Kinetics: speed of a chemical reaction • Equilibrium: how far a reaction goes • Rxn w/ large equilibrium constant --> proceeds nearly to completion • Rxn w/ small equilibrium constant --> barely proceeds at all • 16.1 Fetal Hemoglobin and Equilibrium a. Hb + O 2 ⇌ HbO 2 b. Concentrations of the reactants & products in a rxn at equilibrium are described by the equilibrium constant, K c. Large K: rxn lies far to the right @ equilibrium i. High concentration of products ii. Low concentration of reactants d. Small K: rxn lies far to the left @ equilibrium i. High concentration of reactants ii. Low concentration of products e. K: measure of how far a rxn proceeds f. Systems @ equilibrium respond to changes in ways that maintain equilibrium • 16.2 The Concept of Dynamic Equilibrium a. Reversible: rxn that can proceed in both the forward & reverse directions b. Dynamic equilibrium for a chemical rxn is the condition in which the rate of the forward rxn equals the rate of the reverse rxn c. Concentrations remain constant but the concentrations of reactants & products are not equal to one another • 16.3 The Equilibrium Constant (K) a. aA + bB ⇌ cC + dD b. Equilibrium constant (K): ratio (at equilibrium) of the concentrations of the products raised to their stoichiometric coefficients divided by the concentrations of the reactants raised to their stoichiometric coefficients c. d. Law of mass action: relationship between the balanced chemical equation & the expression of the equilibrium constant e. Expressing Equilibrium Constants for Chemical Reactions i. Ex: 2N 2(g) ⇌ 4NO (2) + O (2) 𝑁𝑂 2] 𝑂2] 1. 𝐾 = [𝑁2 5] 2. Coefficients in the chemical equation become the exponents in the equilibrium constant expression f. The Significance of the Equilibrium Constant i. Large K (K >> 1) 1. Numerator (specifies amounts of products @ equilibrium) is larger than the denominator (specifies amounts of reactants @ equilibrium) 2. Forward rxn is favored ii. Equilibrium constant doesn't say anything about how fast a rxn reaches equilibrium, only how far the rxn has proceeded once equilibrium is reached iii. Small K (K << 1) 1. Reverse rxn is favored 2. More reactants than products @ equilibrium iv. Summarizing: 1. K << 1 Reverse rxn is favored; forward rxn does not proceed very far 2. K ≈ 1 Neither direction is favored; forward rxn proceeds about halfway 3. K >> 1 Forward rxn is favored; forward rxn proceeds essentially to completion g. Relationships between the Equilibrium Constant and the Chemical Equation i. 3 modifications 1. If we reverse the equation, we invert the equilibrium constant 2. If we multiply the coefficients in the equation by a factor, we raise the equilibrium constant to the same factor 3. If we add 2 or more individual chemical equations to obtain an overall equation, we multiply the corresponding equilibrium constants by each other to obtain the overall equilibrium constant • 16.4 Expressing the Equilibrium Constant in Terms of Pressure a. For gaseous rxns, partial pressure of a gas is proportional to its concentration b. Equilibrium constant can be expressed in terms of the partial pressures of the reactants & products c. K pas same expression as K excepc that the partial pressures are used instead of concentration d. e. If Δn = 0, K p K c f. Units of K i. No units • 16.5 Heterogeneous Equilibria: Reactions Involving Solids and Liquids a. Pure solids & liquids aren't included in the equilibrium expression • 16.6 Calculating the Equilibrium Constant from Measured Equilibrium Concentrations
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