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15.78 You can choose starting concentrations for reactants in the Chemical Equilibrium simulation (eChapter 15.1). (a) Write the equilibrium-constant expression for the reaction in the simulation. (b) Calculate the value of the equilibrium constant. (c) Does this reaction lie to the right or to the left?

15.79 Using the equilibrium constant that you calculated in the previous question for the reaction in the Chemical Equilibrium simulation (eChapter 15.1), predict what the equilibrium concentrations of reactants and products will be if you start with 0.0007 M Fe³⁺(aq) and 0.0004 M SCN^-(aq). Use the simulation to check your answer.

15.80 The significance of an equilibrium constant's magnitude is illustrated in the Equilibrium Constant simulation (eChapter 15.2). Select the A B reaction and carry out several experiments with varying starting concentrations and varying equilibrium constants. Because reactants are favored when K_eq is very small, is it possible to enter a very small value for K_eq, start with only A (no B), and still have only A at equilibrium? Explain.

15.81 In Exercise 15.26 you calculated K_eq for the reaction N₂O₄(g) 2NO₂(g). (a) Which of the reactions in the Equilibrium Constant simulation (eChapter 15.2) best represents the equilibrium between N₂O₄(g) and 2NO₂(g)? (b) Using the simulation, enter the K_eq value from Exercise 15.26 and experiment with various starting concentrations of reactant and products. Can you select starting concentrations of reactants and products such that no change in concentrations is observed? Explain.

15.82 Consider the A B and A 2B reactions in the Equilibrium Constant simulation (eChapter 15.2). Assume that A and B are both gases; A B is an exothermic reaction; and A 2B is an endothermic reaction. For both reactions, state the effect that each of the following changes would have on the value of K_eq, the concentration of B at equilibrium, and the rate of the reaction: (a) increased temperature; (b) increased pressure; and (c) addition of a catalyst.