Kinetics, Thermodynamics and Equilibrium - Revsworld

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Going up the down escalator: This diagram shows different points at which a system can reach equilibrium: TYPES OF EQUILIBRIUM 1) Chemical Equilibrium: The rate of the forward reaction is equal to the rate of the reverse reaction. The Haber Process: used to manufacture ammonia. Why ammonia? To make lots of different cleaning products. This is a multi-billion dollar industry, all based on this simple equilibrium: N 2 (g) + 3 H 2 (g) 2 NH 3 (g) + heat This reaction produces ammonia, but some of the ammonia decomposes to form its original elements. When the rate of synthesis equals the rate of decomposition, this system will be at equilibrium. It is possible to apply stresses to this equilibrium to force it to produce more ammonia. The ratio of amount of product to the amount of reactant at equilibrium is called the EQUILIBRIUM CONSTANT. It is a number that represents how far the reaction went before reaching equilibrium. K eq = [products] / [reactants], where [ ] stands for concentration. Mass Action Expression: a ratio of the concentration of the products to the concentration of the reactants. Used to determine the degree to which the forward reaction proceeded before equilibrium was established. aA + bB cC + dD, where the lower case letters represent the coefficients of the substances in the reaction [C] c [D] d K eq = --------- [A] a [B] b Products over reactants, coefficients become exponents, concentrations are multiplied © 2009, Mark Rosengarten AE 10
For the equilibrium 2 SO 2 (g)+ O 2 (g) 2 SO 3 (g), the mass action expression would be set up as: K eq = [SO 3 ] 2 / [SO 2 ] 2 [O 2 ] For the equilibrium CaCl 2 (s) Ca +2 (aq) + 2 Cl -1 (aq), the mass action expression would be set up as: K eq = [Ca +2 ] [Cl -1 ] 2 / [CaCl 2 ] For the equilibrium 2 O 3 (g) 3 O 2 (g), the mass action expression would be set up as: K eq = [O 2 ] 3 / [O 3 ] 2 Equilibrium Constant (K eq ): the numerical ratio derived from plugging the equilibrium concentrations of the products and reactants and working through the algebra of the mass-action expression Assume that for the system at equilibrium A + B 2C + energy, the equilibrium concentrations of the species are [A] = 2 M [B] = 5 M [C] = 10 M. What is K eq ? K eq = [C] 2 / [A] [B] = [10] 2 / [2] [5] = 100 / 10 = 10 K eq has no units, it is simply a ratio. Evaluating K eq values The value of K eq tells us how much product is formed before equilibrium is attained. The greater the value of K eq , the greater the concentration of products at equilibrium, therefore, the further the reaction went before reaching equilibrium Imagine that escalator we looked at on the first page (diagrammed on the previous page). Imagine that the bottom of the escalator represents the 100% reactants (what you have when the reaction starts) and the top of the escalator represents 100% products (what you have when the reaction goes to completion without reaching equilibrium). Therefore, the following chart describes K eq and its relationship to how far the reaction went before reaching equilibrium: Value of K eq [Products] [Reactants] before reaching equilibrium. K eq = 0 [Products] < [Reactants] The reaction does not start at all... K eq is less than 1 [Products] < [Reactants] The reaction goes a little way K eq = 1 [Products] = [Reactants] The reaction goes halfway K eq is more than 1 [Products] > [Reactants] The reaction goes most of the way K eq = infinity [Products] > [Reactants] The reaction goes to completion Place the following equilibrium constants in order from which system goes the least far towards completion before reaching equilibrium to which system goes the furthest towards completion before reaching equilibrium: a) K eq = 3.4 X 10 -5 b) K eq = 5.7 X 10 7 c) K eq = 9.3 X 10 -9 d) K eq = 2.1 X 10 9 Correct order: Go by exponents first. c, a, b, d © 2009, Mark Rosengarten AE 11
Page 1 and 2: Kinetics, Thermodynamics and Equili
Page 3 and 4: FACTORS THAT AFFECT REACTION RATE B
Page 5 and 6: 2) Potential Energy Diagrams (HW: p
Page 7 and 8: Potential Energy Diagrams: graph th
Page 9: 3) Equilibrium Systems (HW: p. 28,
Page 13 and 14: The more soluble the salt is, the h
Page 15 and 16: 2) ENTROPY - the randomness (disord
Page 17 and 18: The quantity ∆G is Gibbs Free Ene
Page 19 and 20: A/E Reference Table B Energies of F
Page 21 and 22: Catalysts, inhibitors and surface a
Page 23 and 24: Student Name:______________________
Page 25 and 26: D) For the following blank PE Diagr
Page 27 and 28: H) Graph and label a potential ener
Page 29 and 30: 8) Complete the following chart: K
Page 31 and 32: D) For the formation of PbO: 1) Usi
Page 33: C) Complete the following questions

Kinetics, Thermodynamics and Equilibrium - Revsworld

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