1 (311)

Prévia do material em texto

Chapter 15 Chemical Equilibrium 311 15.87 Given: = 0.76; at equilibrium = 1.0 atm Find: Pinitial Conceptual Plan: Prepare an ICE table, represent the with A and the change with x, sum the table, deter- mine the equilibrium values, use the total pressure, and solve for A in terms of x. Determine partial pressure of each at equilibrium, use the equilibrium expression to determine x, and determine A. Solution: C(s) + Pc Initial A constant 0.00 Change -x +2x Equil A 2x = + 1.0 = A - x + 2x A = 1.0 x = (A - x) = (1.0 x) - x = 1.0 2x; = 2x = = (1.0 = 0.76 + 1.52x - 0.76 = 0 Solve the quadratic equation. x = 0.285 or 0.665 so x = 0.285 A = 1.0 x = 1.0 0.285 = 0.715 = 0.72 atm Check: Plug the values into the equilibrium expression: Kₚ = = (A x) = (0.715 0.285) = 0.756 = 0.76; the original equilibrium is constant. 15.89 Given: V = T = 1000 K, Kₚ = 3.9 X 10⁻² Find: mass CaO as equilibrium Conceptual Plan: Kₚ PV = nRT stoichiometry g = n(molar mass) Solution: Because CaCO₃ and CaO are solids, they are not included in the equilibrium expression. Kₚ = Pco₂ = 3.9 X 10⁻²; n = RT PV = (3.9 X 10⁻² = 3.108 X 10⁻⁴ mol CO₂ mol 3.108 10⁻⁴ mol X 1 1 mol X 56.08 1 g CaO = 0.0174 = 0.0174 g CaO Check: The small value of K would give a small amount of products, so we would not expect a large mass of CaO to form. 15.91 Given: = 3.10, initial Pco = 215 torr, = 245 torr Find: mole fraction COCl₂ Conceptual Plan: P in torr P in atm. Prepare an ICE table, represent the change with x, sum the table, 1 atm 760 torr determine the equilibrium values, use the total pressure, and solve for mole fraction. Ptotal 1 atm Solution: = (215 = 0.2829 atm atm CO(g) + Initial 0.2829 0.3224 0 so the reaction shifts to the right. Change -x -x +x Equil 0.2829 x 0.3224 x x = = (0.2829 x x) = 3.10 so 3.10x² - 2.87634x + 0.2827 = 0 Solve using the quadratic equation, found in Appendix I.x = 0.8161 or 0.1117 so x = 0.1117 P is proportional to n under like conditions so the mole fraction can be determined using the pressure values. Copyright © 2017 Pearson Education, Inc.