5 STEPS TO A 5: 500 AP Chemistry Questions to Know by Test Day! (2012)
Chapter 8. Equilibrium (Questions 301–330)
301. Which of the following stresses when applied to the reaction above will result in an increased amount of MgO(s)?
I. Remove Mg(s)
II. Increase the pressure (decrease the volume)
III. Add O2(g)
(A) I only
(B) II only
(C) III only
(D) II and III only
(E) I, II, and III
302. Suppose the reaction represented above is at equilibrium. Which of the following changes will result in an increased amount of O2(g)?
(A) Increasing the pressure
(B) Decreasing the volume
(C) Adding more N2(g)
(D) Decreasing the temperature
(E) Removing NOCl(g)
303. Which of the following statements is true regarding the equilibrium reaction represented above?
(A) Increasing the pressure will shift the equilibrium to the right.
(B) Increasing the temperature will shift the equilibrium to the right.
(C) Adding more C(s) will shift the equilibrium to the right.
(D) Decreasing the temperature will result in the formation of more O2(g).
(E) Adding more O2 will result in the formation of more heat.
304. In which of the following reactions at equilibrium will there be no change in response to a change in the volume of the reaction vessel? (Assume constant temperature.)
(A) SO2Cl2(g) ⇔ SO2(g) + Cl2(g)
(B) H2(g) + Cl2(g) ⇔ 2 HCl(g)
(C) 2 SO2(g) + O2(g) ⇔ 2 SO3(g)
(D) 4 NH3(g) + 5O2(g) ⇔ 4 NO(g) + 6 H2O(g)
(E) 2 N2O(g) + O2(g) ⇔ 2 NO(g)
305. A closed rigid container contains distilled water and H2(g) at equilibrium. Which of the following actions would increase the concentration of H2(g) in the water?
I. Decreasing the temperature of the water
II. Vigorous shaking
III. Injecting more H2(g) into the container
(A) I only
(B) II only
(C) III only
(D) I and III only
(E) I, II, and III
Questions 306–308 refer to the following chemical reaction at equilibrium.
306. Suppose the reaction above occurs in a closed, rigid tank. After it has reached equilibrium, pure N2(g) is injected into the tank at a constant temperature. After it has re-established equilibrium, which of the following has a lower value compared to its value at the original equilibrium?
(A) The amount of NH3(g) in the tank
(B) The amount of H2(g) in the tank
(C) The amount of N2(g) in the tank
(D) Keq for the reaction
(E) The total pressure in the tank
307. Which of the following changes, if occurred alone, would cause a decrease in the value of Keq for the reaction represented above?
(A) Adding a catalyst
(B) Lowering the temperature
(C) Raising the temperature
(D) Decreasing the volume
(E) Increasing the volume
308. When the reaction represented above is at equilibrium, the ratio
can be increased by which of the following?
I. Increasing the pressure
II. Decreasing the pressure
III. Increasing the temperature
IV. Decreasing the temperature
(A) I only
(B) I and III only
(C) I and IV only
(D) II and III only
(E) II and IV only
Questions 309–311 refer to the following reaction.
309. The molar equilibrium concentrations for the reaction mixture represented above at 298 K are [X] = 4.0 M, [Y] = 5.0 M, and [Z] = 2.0 M. What is the value of the equilibrium constant, Keq, for the reaction at 298 K?
(A) 0.06
(B) 2.50
(C) 16.0
(D) 62.5
(E) 105.5
310. Which of the following changes to the equilibrium system shown above will result in an increased quantity of Z?
I. Increasing the pressure
II. Decreasing the temperature
III. Adding more X(g)
(A) I only
(B) II only
(C) III only
(D) II and III only
(E) I, II, and III
311. Changes to the equilibrium system above that will increase the ratio of
include which of the following?
I. Decreasing the pressure
II. Increasing the temperature
III. Adding more X(g)
(A) I only
(B) II only
(C) I and III only
(D) II and III only
(E) I, II, and III
312. The diagram above represents a mixture of F2 and F gases in a 1.0-L container at equilibrium according to the equation F2 ⇔ 2 F at a temperature above 1,200 K. Which of the following is true of the equilibrium constant for this reaction at this temperature?
(A) K < 0
(B) K = 0
(C) 0 < K < 1
(D) K = 1
(E) K > 1
313. At 500 K, the Keq for the reaction above is 2.5 × 1010. What is the value of Keq for the reverse reaction at 500 K?
(A) –2.5 × 1010
(B) 2.5 × 10−10
(C) 2.5 × 10−11
(D) 4.0 × 1010
(E) 4.0 × 10−11
314. A soluble compound XY3 dissociates in water according to the equation above. If, in a 0.06-m solution of the compound, 30.0 percent of XY3 dissociates, which of the following is closest to the number of moles of particles of solute per 1.0 kg of water?
(A) 0.018
(B) 0.060
(C) 0.072
(D) 0.114
(E) 0.240
315. What is the molar solubility of BaSO4(s) in water? (The Ksp for BaSO4(s) is 1.1 × 10−10.)
(A) 5.5 × 10−11 M
(B) 1.10 × 10−10 M
(C) 1.05 × 10−5 M
(D) 5.5 × 10−5
(E) 5.5 × 10−10 M
316. What is the molar solubility of CaF2(s) in water? (The Ksp for CaF2(s) is 4.0 × 10−11.)
(A) (4.0 × 10−11)1/2 M
(B) (1.0 × 10−11)1/2 M
(C) 4.0 × 10−11 M
(D) (4.0 × 10−11)1/3 M
(E) (1.0 × 10−11)1/3 M
317. A saturated solution of metal hydroxide M(OH)2, has a pH of 10.0 at 25°C. What is the Ksp value for M(OH)2?
(A) 5 × 10−31
(B) 1 × 10−20
(C) 5 × 10−13
(D) 2.5 × 10−9
(E) 1 × 10−8
318. Iron (II) hydroxide is sparingly soluble. Its solvation in water is represented by 
. True statements about the solubility of iron (II) hydroxide include:
I. Increasing the pH reduces its solubility
II. Decreasing the pH reduces its solubility
III. The value of Ksp for the reaction is specific to the pH of the solution in which it is dissolved.
(A) I only
(B) II only
(C) III only
(D) I and II only
(E) I, II, and III
319. A solution contains 0.2 M Ba2+ and 0.2 M Ca2+. Which of the following CrO42– concentrations will precipitate as much Ba2+ as possible without precipitating any CaCrO4? (The Ksp of BaCrO4 = ~1 × 10-10 and the Ksp of CaCrO4 = ~7 × 10−4.)
(A) 3.5 × 10−3 M
(B) 7 × 10−4 M
(C) 1.5 × 10−7 M
(D) 5 × 10−10 M
(E) 7 × 10−14 M
320. The figure above shows two completely sealed containers, a 10-mL tube, and a 1,000-mL bowl, each filled to a fraction of its volume with methanol. In a laboratory at 1 atm and 25°C, the vapor pressure of the methanol is
(A) lower in Container 1 because the volume of methanol is lower.
(B) higher in Container 1 because the volume of the container above the methanol is smaller.
(C) higher in Container 2 because the surface area of the methanol is larger.
(D) higher in Container 2 because the volume of the container above the methanol is greater.
(E) equal in Containers 1 and 2 because they are at the same temperature.
321. The vaporization of a liquid is represented in the equation above. Which of the following most accurately accounts for the fact that the vapor pressure of liquids increases with increasing temperature?
(A) Vaporization is exothermic.
(B) A liquid at a particular temperature continues to vaporize until it has completely evaporated.
(C) If a chemical system at equilibrium experiences a change in temperature, the equilibrium shifts to counteract the change.
(D) The condensation of gases takes longer than the vaporization of liquids.
(E) The condensation of gases releases more energy than is absorbed by vaporizing liquids.
322. Which of the following best accounts for the fact that, at the same altitude, the partial pressure of water vapor in the atmosphere can increase significantly with increasing temperature, but the partial pressures of N2, O2, Ar, and CO2 stay relatively constant?
(A) The vapor pressures of N2, O2, Ar, and CO2 are much greater than that of H2O.
(B) The water cycle (evaporation, condensation, precipitation) causes water to constantly change between liquid and gas phases.
(C) The conditions required for atmospheric N2, O2, Ar, and CO2 to be in equilibrium with their liquid phases do not exist on the earth’s surface.
(D) Water in the atmosphere constantly forms water droplets around condensation nuclei whereas N2, O2, Ar, and CO2 only condense in or above the stratosphere.
(E) Water vapor is constantly being added to the atmosphere by cellular respiration and combustion.
323. Consider a closed, adiabatic system consisting of a mixture of liquid and solid substance Z at equilibrium at its melting point. Which of the following statements is true regarding the system?
(A) The entropy of the system is at a maximum.
(B) The entropy of the system is at a minimum.
(C) The entropy of the system will increase over time.
(D) The entropy of the system is zero.
(E) The entropy of pure substances does not change if at a constant temperature.
Questions 324–328 refer to the information in the table below.
324. Which of the following is true regarding the strengths of HOCl and HOBr?
(A) HOBr is a stronger acid because Br is a larger atom than Cl, and loses its proton more easily than HOCl.
(B) HOCl is a stronger acid because Cl is more electronegative than HOBr.
(C) The strengths of HOCl and HOBr are dependent on the pH of their respective solutions.
(D) The strengths of HOCl and HOBr are dependent on their respective concentrations.
(E) HOBr is the stronger acid because the negative log of its Ka, the pKa, is larger than that of HOCl.
325. Which of the following statements is the most accurate prediction about the strength of acid HOI?
(A) HOI is the strongest acid because I is a larger atom than Br and Cl, and therefore the proton dissociates more readily in solution.
(B) HOI is the strongest acid because the O−H bond in HOI is stronger than the OH bond in HOCl or HOBr.
(C) HOI is the weakest acid because its conjugate base, OI−, is less stable than the conjugate bases of HOCl and HOBr.
(D) The strength of HOI is dependent on the concentrations and pH of its solution.
(E) HOI is the stronger acid than HOBr and HOCl because the negative log of its Ka, the pKa, is larger than the pKa of HOBr and HOCl.
326. Which of the following is the correct name for HOCl?
(A) Hydrochloric acid
(B) Hypochloric acid
(C) Hypochorous acid
(D) Perchlorous acid
(E) Hydrogen chloride
327. The hydrolysis of KOCl is represented above. Which of the following is the correct set up for determining the equilibrium constant of the reaction?
(A) 2.9 × 10−8 = [OH−][HOCl]/[OCl−]
(B) 2.9 × 10−8 = [OH−][HOCl]/[OCl−][H2O]
(C) 1 × 10−14 = [OH−][2.9 × 10−8]/[OCl−]
(D) Kb = 1.0 × 10−14/2.9 × 10−8
(E) Kb = 2.9 × 10−8/1.0 × 10−14
328. Which of the following shows the correct way to calculate the [OH−] concentration in a 1.5-M solution of KOCl at 298 K? Assume the Khydrolysis = 3.4 × 10−7.
Questions 329 and 330 refer to the reaction A ⇔ B. The concentrations of A and B throughout the reaction are shown in the figure below.
329. Which of the following statements is true regarding the progress of the reaction?
(A) At point X, the rate of A→B equals the rate B→A.
(B) From 0.0 to 0.8 sec, the concentration of Reactant A is increasing.
(C) From 0.0 to 0.8 sec, the rate of A→B exceeds the rate of B→A.
(D) After 1 sec, the reaction has gone to completion.
(E) If the reaction was observed after 10 minutes, the concentrations of A and B would be equal.
330. Suppose at time 1.5 sec, more B was added to the system (enough to momentarily raise the concentration to 0.25 M). In which of the following ways is the system expected to respond?
(A) The forward reaction would be pushed to completion, consuming all of Reactant A.
(B) The equilibrium state would be overwhelmed and the excess B would precipitate.
(C) The equilibrium state would be overwhelmed forcing the reverse reaction to go to completion.
(D) The concentration of A would increase.
(E) The equilibrium would adjust to consume the excess B and produce a new ratio of [A]/[B].