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Chapter 13: Chemical Equilibrium

Chapter 13: Chemical Equilibrium. Introduction to Equilibria Equilibrium Constants Heterogeneous Equilibria Applications of the Equilibrium Expression – solving equilibrium problems! LeChatelier’s Principle. Figure 13.5 N 2 + 3H 2 2 NH 3. Figure 13.4. Table 13.1. EXAMPLE 1:.

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Chapter 13: Chemical Equilibrium

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  1. Chapter 13: Chemical Equilibrium • Introduction to Equilibria • Equilibrium Constants • Heterogeneous Equilibria • Applications of the Equilibrium Expression – solving equilibrium problems! • LeChatelier’s Principle

  2. Figure 13.5 N2 + 3H2 2 NH3

  3. Figure 13.4

  4. Table 13.1

  5. EXAMPLE 1: In a sealed, 10.5 L vessel at 184°C, equilibrium is reached for the following reaction: 2 NO2 (g) 2 NO (g) + O2 (g) At equilibrium, the vessel is found to contain 1.353 g NO2, 0.0960 g of NO, and 0.0512 g of O2. Find the values of Kc and Kp for this reaction.

  6. EXAMPLE 2: A 0.682 gram sample of ICl(g) is placed in a 625 mL reaction vessel at 682 K. When equilibrium is reached for the reaction below, 0.0383 g of I2 is found in the mixture. Find Kc for this reaction. 2 ICl(g) I2 (g) + Cl2 (g)

  7. EXAMPLE 3: If 0.850 moles of N2 and 0.850 moles of O2 gases are placed in a 8.00 L vessel at 3900°C, the following reaction occurs: N2 (g) + O2 (g) 2 NO (g) The equilibrium constant for this reaction, K, is 0.0123 at 3900°C. Find the equilibrium concentrations of all three gases.

  8. EXAMPLE 4: If 1.00 mole of carbon dioxide gas is exposed to a hot carbon surface at 800°C in a 1.00 L vessel, the following reaction occurs with an equilibrium constant, K, of 14.0. Find the equilibrium concentration of each gas. C(s) + CO2 (g) 2 CO (g)

  9. EXAMPLE 5: What if both reactants and products are included in the initial mixture? Find the equilibrium concentrations of all three gases if 2.0moles of H2, 2.0 moles of I2, and 2.0 moles of HI are placed in a 500 mL vessel at room temperature. At this temperature, K = 49.7. H2 (g) + I2 (g) 2 HI (g)

  10. Dealing with Cubic Equations Some problems can give a cubic equation to solve. In some cases, we can deal with this by assuming the change in concentration to be very small compared to the initial concentrations. We must consider the size of K and the direction of the shift to know when this assumption is good.

  11. Example 6: Cubic, small K At 35°C, K = 1.6 x 10-5 for the reaction below. 2 NOCl (g) 2 NO (g) + Cl2 (g) If 3.0 moles of pure NOCl are placed in a 2.0 L flask at 35°C, find the concentrations of all species in the flask at equilibrium.

  12. Example 7: Cubic, large K At 25°C, K = 7.16x102 for the reaction below. 2 SO2Cl (g) 2 SO2 (g) + Cl2 (g) If 2.00 moles of SO2Cl are placed in a 1.00L flask at 25°C, find the concentrations of all species in the flask at equilibrium.

  13. Example 8: Quadratic, large K If 0.10 mole of Fe(NO3)3 is added to 1.0 L of 2.0 M KSCN, find the equilibrium concentrations of Fe3+, SCN-, and FeSCN2+. K = 1.1 x 103. Fe 3+ (aq) + SCN-(aq) FeSCN2+(aq)

  14. Example 9: Cubic, large shift If 2.0 atm of SO2 and 1.0 atm of O2are placed in otherwise evacuated container, what will be the partial pressures of all gases in the container at equilibrium? 2 SO2 (g) + O2 (g) 2 SO3 (g) Kp = 0.25 at25°C

  15. Example 10: LeChatelier’s Principle Consider the following reaction: PCl3 (g) + Cl2 (g) PCl5 (g) ; DH = -92 kJ Indicate whether the number of moles of PCl3 will increase, decrease or remain the same when the following changes are made to the system at equilibrium. a) The temperature is decreased. b) Cl2 is added. c) PCl5 is added. d) The volume is decreased. e) The total pressure is increased by the addition of argon gas. f) A catalyst is added.

  16. Example 11: LeChatelier’s Principle Consider the following reaction: CoCl42- (aq) + 6 H2O(l) Co(H2O)62+ (aq) + 4 Cl- (aq) Indicate whether the reaction will shift to the left, to the right, or not at all when each of the following changes is made to this system while it is at equilibrium. a) NaCl is added. b) AgNO3 is added forming a precipitate of AgCl(s). c) H2O is added.

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