AP MCQ 07ABCDEFGHIJKLMN PART 1 Question 01: It is observed that when hexaaquacobalt(II) ions are exposed to chloride ions, that the reaction shown below occurs, and when equilibrium has been established, that the beaker’s contents are purple in color. What does the observation of a purple color alone, suggest about the equilibrium reaction mixture? [Co(H2O)6]2+(aq) (red) + 4Cl-(aq) ⇌ [CoCl4]2-(aq) (blue) + 6H2O(l) The equilibrium mixture is made up of 50% red species and 50% blue species The equilibrium contains both red and blue species but in unknown amounts The equilibrium mixture lies heavily to the left The equilibrium mixture lies heavily to the right Question 02: Which expression correctly characterizes the relationship between Q and K at equilibrium? Q = K Q = -K Q-1 = K Q = K-1 Question 03: What is true of any reversible reaction reaction that has reached equilibrium? All products and reactants will have the same concentrations The reaction has stopped There is a specific ratio of products to reactants at a specific temperature Less products will be produced if the reaction is cooled Questions 04-06: The chemical reaction below has Kc = 5.0 at a temperature of 2000 K. H2(g) + CO2(g) ⇌ H2O(g) + CO(g) In an experiment, 2.0 moles of H2(g), 2.0 moles of CO2(g), 1.0 mole of H2O(g) and 1.0 mole of CO(g) are brought together in a 1.0 L container at 2000 K. Question 04: What happens to the concentration of CO2(g), as the mixture approaches equilibrium? It remains at 2.0 M, since the reaction mixture is already at equilibrium because Kc is fixed at a fixed temperature It remains at 2.0 M, since the reaction is already at equilibrium It decreases since the reaction will proceed forward in order to reach equilibrium It increases since the reaction will proceed backward in order to reach equilibrium Question 05: Once equilibrium has been established at 2000 K, what would be the effect on Kc, and the effect on the concentration of CO(g), if a sample of hydrogen gas were injected into the reaction vessel in such a way that the temperature remained constant and the system was allowed to reach equilibrium once more? [CO(g)] increases and K decreases [CO(g)] increases and K remains constant [CO(g)] increases and K increases [CO(g)] decreases and K remains constant Question 06: What is the Kc for the reaction shown below? 2H2O(g) + 2CO(g) ⇌ 2H2(g) + 2CO2(g) 10 25 1/10 1/25 Question 07: A weak diprotic acid, H2X, is known to dissociate in two separate steps. If the equilibrium constant for step 1 (the loss of one H+ ion) is called A, and the equilibrium constant for step 2 (the loss of the second proton from HX-) is called B, What is the equilibrium constant for the reaction below? H2X ⇌ 2H+ + X- (A)+(B) (A)/(B) (A)(B) (B)/(A) Question 08: Which of the following changes cause the equilibrium constant K, for any reaction, to change? Adding products to the equilibrium mixture Adding reactants to the equilibrium mixture Changing the temperature Increasing the pressure while keeping all other variables the same Question 09: 1 mole of PCl5(g) introduced into and evacuated container and is heated until the following equilibrium is established. Which of the following statements is true? PCl5(g) ⇌ PCl3(g) + Cl2(g) At equilibrium the total moles in the container will be greater than 1 PCl3 and Cl2 will be present in differing amounts The amount of PCl5(g) will remain constant As the reaction proceeds from the initial conditions to the equilibrium position, the mole fraction of PCl3(g) decreases Question 10: At a particular temperature, the equilibrium partial pressures of SO2(g), O2(g) and SO3(g) in the equilibrium mixture shown below, are found to be 1.0 atm, 0.5 atm and 3.0 atm respectively. What is the value of Kp at this temperature? 2SO2(g) + O2(g) ⇌ 2SO3(g) 0.5/9.0 3 6 18 Δ
