AP Chem Unit 8 Test MC
The synthesis of NH3 is represented by the equation above. Based on the equilibrium constant K, and ΔH rxn given above, which of the following can best be used to justify that the reaction is thermodynamically favorable at 298 K and constant pressure?
B
According to the information about the dissolution of Ba(IO3)2 shown above, the correct value of S, the molar solubility of Ba(IO3)2, can be calculated using with of the following mathematical relationships?
4S^3 = 4 x 10 ^ -9 M
Ca(OH)2 precipitates when a 1.0 g sample of CaC2 is added to 1.0 L of distilled water at room temperature. If a 0.064 g sample of CaC2 (molar mass 64 g/mol) is used instead and all of it reacts, which of the following will occur and why? (The value of Ksp for Ca(OH)2 is 8.0 x 10 ^-8)
Ca(OH)2 will not precipitate because Q < Ksp
The exothermic dissolution of Mg(OH)2 in water is represented by the equation above. The Ksp of Mg()H)2 is 1.8 x 10 ^ -11. Which of the following changes will increase the solubility of Mg(OH)2 in an aqueous solution?
Decreasing the pH
The decomposition of HI at 298 K is represented by the equilibrium equation above. When 100. torr of HI is added to a previously evacuated, rigid container and allowed to reach equilibrium, the partial pressure of I2 repeated at the same temperature, which of the following correctly predicts the equilibrium partial pressure I2 and why?
I2 = 7.4 torr, because it is directly proportional to the initial pressure of HI.
The chemical equations and equilibrium expressions for two reactions at the same temperature are given above. Based on the information, which of the following expressions can be used to calculate the value of K3 for reaction 3 at the same temperature?
K3 = 1/K1 x 1/K2
Based on the equilibrium constants given above, which of the following gives the correct expression for the equilibrium constant for reaction 3?
K3 = K2/K1
The table above lists some equilibrium systems and their equilibrium constants. Which of the following identifies the correct mathematical relationship that uses the information to calculate K5?
K5 = K1 x K3 / K4
A sample of POCl3 is placed in a closed, rigid container at 298 K and allowed to reach equilibrium according to the equation above. Based on the value for ΔG rxn = +490 kJ/mol, which of the following is true?
K=e^-490,000/8.314 x 298 << 1 and at equilibrium POCl3 >> PCl3
based on the Ksp values in the table above, a saturated solution of which of the following compounds has the highest [Cl]?
PbCl2
The system represented by the equation above is allowed to establish equilibrium. The initial pressures of the substances are given in the table. Which of the following explains what the system will do as it approaches equilibrium?
Q = (80)^2 / (10)^2 (2.0) > Kp and equilibrium will be approached by consuming NOBr because the reverse reaction is faster than the forward reaction.
Which of the following is true if the volume of the container is decreased by one half?
Q = 1000, and the reaction will proceed toward products
The equilibrium reaction between Cl2 and H2O at 25 C is represented by the chemical equation shown above. If a solution at equilibrium at 25 C is diluted with distilled water to twice its original volume, which of the following gives the value for Qc and predicts the response by the system immediately after dilution?
Qc = Ke/4, and the rate of the forward reaction will be greater that the rate of the reverse reaction
A sealed rigid vessel contains BaO2 in equilbrium with BaO and O2 as requested by the equation above. Which of the following changes will increase the amount of BaO2 in the vessel?
Removing a small amount of BaO
When colorless solutions containing Fe ions and SCN ions are combined, a deep-red complex ion, FeSCN quickly forms, as shown in the net ionic equation above. Which of the following explains the observation that adding a few additional crystals of KSCN results in the red color of the solution becoming deeper?
The added KSCN dissolves, causing the reaction system to respond by producing more product to partially consume SCN and reduce its concentration.
Two students prepared aqueous solutions of LiCl and measured the properties, as shown in the table above. Both students observed that the solid LiCl readily dissolved in H2O. The students drew particle diagrams to explain the changes in enthalpy and entropy of dissolution for LiCl based on their results and observations. Based on this information, the better particle diagram was drawn by which student, and why is that diagram more accurate?
The better particle diagram was drawn by student 1 because when LiCl dissolves in water, it dissociates into Li and Cl ion causing an increase in entropy.
A saturated aqueous solution of CdF2 is prepared. The equilibrium in the solution is represented above. In the solution, [Cd]eq = 0.0585 M and [F]eq = 0.117 M. Some 0.90 M NaF is added to the saturated solution. Which of the following identifies the molar solubility of CdF2 in pure water and explains the effect that the addition of NaF has on this solubility?
The molar solubility of CdF2, in pure water is 0.0585 M, and adding NaF decreases this solubility because the equilibrium shifts to favor the precipitation of some CdF2.
A saturated solution of MgCO3 at equilibrium is represented by the equation above. Four different saturated solutions were prepared and kept at the same temperature. A given amount of HCl was added to each solution and data were collected to calculate the molar solubility of MgCO3 as shown in the table above. Which of the following can be concluded from the data?
The molar solubility of MgCO3 increases with increasing acidity (lower pH)
At 298 K, NH4NO3 readily dissolves in water, suggesting that the change in free energy (ΔG) favors the dissolution process. However, when NH4NO3 dissolves in water, the temperature of the water decreases. The particulate diagram above attempts to provide a microscopic view of the dissolution of NH4NO3 considering both the change in enthalpy (ΔH) and the change in entropy (ΔS). Which of the following explains what the particle diagram is able to illustrate and why?
The particle diagram is able to illustrate that entropy increases when NH4NO3 dissolves in water because the ions disperse in solution.
Shown above is the chemical equation for the dissolution of the slightly soluble salt CuBr. Its Ksp value in pure water was experimentally determined. CuBr was found to be mush less soluble in a .001 M NaBr solution than in pure water. Which og the following correctly explains the decrease in solubility of CuBr in .001 M NaBr?
The presence of additional Br ions already in the solution means equilibrium will be reached when much less CuBr has dissolved
A reversible reaction is represented by the equation above. The amounts of reactants and products at time 1 are shown in the particle diagram on the left. The particle diagram on the right shows the amounts of reactants and products at time 2. Based on the diagrams, what can be inferred about the relative rates of the forward and reverse reactions between time 1 and time 2?
The rate of the forward reaction is greater that the rate of the reverse reaction
In an experiment X and Y were combined in a rigid container at constant temperature and allowed to react as shown in the equation above. The table provides the data collected during the experiment. Based on the data, which of the following claims is most likely correct?
The reaction reached equilibrium between 75 minutes and 155 minutes after the reactants were combined because the concentrations X and XY remained constant.
Shown above is information about the dissolution of AgCl in water at 298 K. In a chemistry lab a student wants to determine the value of s, the molar solubility of AgCl, by measuring [Ag] in a saturated solution prepared by mixing excess AgCl and distilled water. How would the results of the experiment be attend if the student mixed excess AgCl with tap water (in which [Cl] = 0.010 M) instead of distilled water and the student did not account for the Cl in the tap water?
The value obtained for Ksp would be too small because less AgCl would dissolve because of the common ion effect due to the Cl already in the water
A 2.0 mol sample of CO and a 2.0 mol sample of H2O are introduced into a previously evacuated 100 L rigid container, and the temperature is held constant as the reaction represented above reaches equilibrium. Which of the following is true at equilibrium?
[CO2] > [CO]
A 1.0 mol sample of CO and a 1.0 mol sample of H2 are pumped into a rigid, previously evacuated 2.0 L reaction vessel at 438 K. Which of the following is true at equilibrium?
[H2] < [CO]
A 1.0 sample of X and a 1.0 mol sample of Q are introduced into an evacuated, rigid 10.0 L container and allowed to reach equilibrium at 50 C according to the equation above. At equilibrium, which of the following is true about the concentrations of the gases?
[R] = [Z] > [Q]
On the basis of the information above, the dissolution of FeF2 in acidic solution is
thermodynamically favorable, because K3 > 1
NH3 was synthesized at 200 C in the presence of a powdered Os(s) catalyst, leading to the equilibrium system represented above. Which of the following changes would result in more NH3 in the mixture after equilibrium is reestablished?
Adding some N2
COCl2 decomposes according to the equation above. When pure COCl2 is injected into a rigid, previously evacuated flask at 690 K, the pressure in the flask is initially 1.0 atm. After the reaction reached equilibrium at 690 K, the total pressure in the flask is 1.2 atm. What is the value of Kp for the reaction at 690 K?
B
