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Chemical Equilibrium

Chemical Equilibrium

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Chemical Equilibrium

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  1. Chemical Equilibrium Outline Reversibility of Reactions Homogeneous Equilibrium Le Châtelier’s Principle Equilibrium Constants Heterogeneous Equilibrium Catalyst Chapter 14

  2. What is dynamic equilibrium?

  3. What happens to the reactions rates at equilibrium?

  4. CO (g) + H2O (g)  H2 (g) + CO2 (g)

  5. N2 (g) + 3 H2 (g) 2 NH3 (g)

  6. The Effect of Concentration Changes on Equilibrium When NO2 is added, some of it combines to make more N2O4 Tro: Chemistry: A Molecular Approach, 2/e

  7. The Effect of Concentration Changes on Equilibrium When N2O4 is added, some of it decomposes to make more NO2 Tro: Chemistry: A Molecular Approach, 2/e

  8. Initial and Equilibrium Concentrations forH2 (g) + I2 (g)  2HI (g) @ 445 °C Tro: Chemistry: A Molecular Approach, 2/e

  9. How does temperature affect Kc for exothermic reactions?

  10. How does a catalyst change the equilibrium constant?

  11. Chapter 14: Examples – Le Châtelier’s Principle Answer the following about the following reaction: N2 (g) + 3 H2 (g) 2 NH3 (g) Kc = ? Change Direction of Shift (, , nc) • Add N2 • Remove H2 • Add NH3 • Increase pressure

  12. Chapter 14: Examples – Le Châtelier’s Principle Answer the following about the following reaction: CH4 (g) + H2O (g) CO (g) + 3 H2 (g)∆H = +206 kJ Kc = ? Change Direction of Shift (, , nc) • Increase CH4 • Increase temperature • Reduce volume

  13. How are Q and K related?

  14. Q, K, and the Direction of Reaction

  15. Chapter 14: Examples – Equilibrium The decomposition of phosphorus pentachloride gas produces phosphorus trichloride and chlorine gases. A 1.10 M sample of phosphorus pentachloride is held at 250 ˚C, when equilibrium is attained its concentration is 0.33 M. Calculate Kc. PCl5 (g) PCl3 (g) + Cl2 (g)

  16. Chapter 14: Examples – Equilibrium Suppose that in the equilibrium between hydrogen chloride, hydrogen and chlorine gases the concentration of hydrogen gas is 1.0 x 10-17 M and that of chlorine gas is 2.0 x 10-16 M. Given: H2 (g) + Cl2 (g) 2 HCl (g) • What is the equilibrium molar concentration of hydrogen chloride, given that Kc = 4.0 x 1031 for the reaction? • What is Kp at 28 ˚C?

  17. Chapter 14: Examples – Equilibrium Sulfur trioxide decomposes at high temperatures to sulfur dioxide and oxygen gases in a closed container. At 1000 K, the initial concentration of sulfur trioxide is 5.22 x 10-3 M. At equilibrium the sulfur trioxide concentration is 2.59 x 10-3 M. What is Kc at 1000 K? 2 SO3 (g) 2 SO2 (g) + O2 (g)

  18. Chapter 14: Examples – Equilibrium Nitrogen dioxide decomposes at high temperatures to nitrogen monoxide and oxygen gases. Initially pure nitrogen dioxide gas is at 0.500 atm and 1000 K. If the total pressure is 0.732 atm at equilibrium, what is Kp? 2 NO2 (g) 2 NO (g) + O2 (g)

  19. Chapter 14: Examples – Equilibrium If S2 has an initial concentration of 2.00 M and there is 150. g of carbon, how many grams of carbon disulfide will there be in a 5.00 L flask at equilibrium? Given: S2 (g) + C (s) CS2 (g) Kc = 9.40 at 900 ˚C

  20. Chapter 14: Examples – Equilibrium Calculate the equilibrium concentrations of iodine chloride, iodine, and chlorine gases, when 0.88 mol I2, and 0.88 mol Cl2 are added to a 1.5 L reaction flask. The concentration equilibrium constant for the reaction is 0.11. 2 ICl (g) I2 (g) + Cl2 (g)

  21. Chapter 14: Examples – Equilibrium At 700 K elemental hydrogen and iodine gases react to produce hydrogen iodide gas. Given: H2 (g) + I2 (g) 2 HI (g)Kc = 54 • Write the equilibrium expression for Kc. • What is the concentration equilibrium constant, Kc´, if the reaction is rewritten as: 2 H2 (g) + 2 I2 (g) 4 HI (g) • How are Kc and Kc´ related? • What is the concentration equilibrium constant, Kc´´, if the original reaction is reversed? • How are Kc and Kc´´ related?

  22. Chapter 14: Examples – Equilibrium What is the pressure equilibrium constant for the reaction: 2 P (g) + 5 Cl2 (g) 2 PCl5 (g) Given the following reactions: 2 P (g) + 3 Cl2 (g)  2 PCl3 (g) Kp1 = 1.72 atm PCl3 (g) + Cl2 (g)  PCl5 (g) Kp2 = 3.99 atm PCl3 (g) + Cl2 (g)  PCl5 (g) Kp3 = 2.11 atm

  23. Chapter 14: Examples – Equilibrium If the initial concentration of methane, CH4, is 0.0625 M, what is it’s equilibrium pressure? Given: 2 H2 (g) + C (s) CH4 (g) Kp = 0.263 atm-1 at 1,000 ˚C

  24. What are some special types of equilibrium constants? • Solubility constant, Ksp • Ca(OH)2 (s)  Ca2+ (aq) + 2 OH- (aq) Ksp = [Ca+2][OH-]2 • Water ionization, Kw • 2 H2O (l)  H3O+ (aq) + OH- (aq) Kw = [H3O+][OH-] • Acid ionization, Ka • HCN (aq) + H2O (l)  H3O+ (aq) + CN- (aq) • Ka= [H3O+][CN-]/[HCN] • Base ionization, Kb • NH3 (aq) + H2O (l)  NH4+ (aq) + OH- (aq) • Kb=[NH4+][OH-]/[NH3]

  25. Chapter 14: Examples – Successive Approximation Oxygen gas reacts with itself to form ozone, O3. If 0.211 atm of oxygen are placed in a flask, what are the equilibrium concentrations of all species? Given: 3 O2 (g) 2 O3 (g) Kp = 1.1 x 10-50 atm-1

  26. Chapter 14: Examples – Successive Approximation If a 0.500 L flask containing 1.25 x 10-4 moles of hydrogen sulfide gas is heated to 800 °C, find the equilibrium concentrations. Given: 2 H3S (g) 2 H2 (g) + S2 (g) Kc = 1.67 x 10-7 M

  27. Chapter 14: Examples – Successive Approximation If the initial concentration of reactants are NH3(g) = 2.70 atm; N2 (g) = 3.00 atm; and H2 (g) = 4.60 atm. What are the equilibrium concentrations of all species? Given: 2 NH3 (g) N2 (g) + 3 H2 (g) Kp = 2.7 x 106 atm2

  28. Chapter 14: Examples – Successive Approximation Calculate the equilibrium concentrations of all species when 1.89 moles of A and 1.075 moles of B are placed in a 0.500 L container at 775 K. Given: A (g) + 2 B (g) 2 C (g) + 2 D (g) Kc = 0.011 M

  29. Chapter 14: Examples – Successive Approximation An evacuated flask is filled with sufficient hydrogen and iodine gases so that the concentration of each gas is 0.620 M. It is then heated to 298 K. What is the concentration gas when equilibrium is established? Given: H2 (g) + I2 (g) 2 HI (g) Kc = 794 at 298 K