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300 Chapter 15 Chemical Equilibrium [H₂] [I₂] [HI] Initial 0.103 0.104 0.00 Because HI gained 0.193 M, H₂ and I₂ had to lose Change -0.0965 +0.193 0.193/2 = 0.0965 M from the stoichiometry of -0.0965 the balanced reaction. Equil 0.0065 0.0075 0.193 Kc = = (0.0065)(0.0075) 764 Check: The units (none) are correct. The magnitude is reasonable (764) since there are higher concentrations of the products than the reactants. The Reaction Quotient and Reaction Direction 15.47 Given: Kc = 8.5 X 10⁻³; [NH₃] = 0.166 M; [H₂S] = 0.166 M Find: whether solid will form or decompose Conceptual Plan: Calculate Q compare Q and Kc Solution: Q = = (0.166)(0.166) = 0.0276 Q = 0.0276 and Kc = 8.5 X 10⁻³ so Q > Kc and the reaction will shift to the left; so more solid will form. 15.49 Given: 6.55 g Ag₂SO₄, 1.5L solution, Kc = 1.1 X 10⁻⁵ Find: whether more solid will dissolve Conceptual Plan: g mol [Ag₂SO₄] calculate Q and compare to Kc 1 mol Ag₂SO₄ mol [] = Q = vol solution Solution: 0.0210 mol Ag₂SO₄ = 1.5 L solution [Ag⁺] = Ag₂SO₄] = 2(0.0140 = 0.0280 = [Ag₂SO₄] = 0.0140 M Q = = = X 10⁻⁵ Q = Kc, the system is at equilibrium and is a saturated solution. Therefore, if more solid is added, it will not dissolve. Finding Equilibrium Concentrations from Initial Concentrations and the Equilibrium Constant 15.51 (a) Given: [A] = 1.0 M, [B] = 0.0, Kc = 4.0; a = 1,b = 1 Find: [A],[B] at equilibrium Conceptual Plan: Prepare an ICE table, calculate Q, compare Q and Kc, predict the direction of the reac- tion, represent the change with x, sum the table, determine the equilibrium values, put the equilibrium values in the equilibrium expression, and solve for x. Determine [A] and [B]. Solution: A(g) B(g) [A] [B] Initial 1.0 0.00 Change -x +x Equil 1.0 x [B] 0 Q = = = Therefore, the reaction will proceed to the right by x. [A] 1.0 Kc = [A] [B] = (1.0 (x) = 4.0; x = 0.80 Check: Plug the values into the equilibrium expression: 0.80 0.20 4.0 Copyright © 2017 Pearson Education, Inc.