Ap chemistry Unit 7 Progress Check: MCQ

A chemist carried out the reaction at 573K, starting with 0.100mol of each reactant in a 1.00L container with variable volume. The reaction mixture quickly reached equilibrium, as indicated in the graph above. The chemist reduces the volume of the equilibrium system by half while keeping the temperature constant. Which of the following predictions about the yield of the reaction is best, and why?

A. By halving the volume, the pressure doubles. The system will respond to the increase in pressure by decreasing the total number of moles of gas in the system. Thus, the yield will increase because the reaction will shift toward more product.

The table above provides the Keq values for two reactions. Which of the following is the correct mathematical expression needed to determine the equilibrium constant of the reaction shown below?

A. K3=K1×1/K2

At a given temperature, the system represented by the chemical equation above is at equilibrium inside a rigid container. Which of the following explains how the system will restore equilibrium, based on the correct relationship between Q and K, after a certain amount of Cl2(g) is added?

A. Since Q=[Cl2][CO]/[COCl2], when Cl2(g) is added to the system Q>KQ>K and the system will restore equilibrium by producing more COCl2(g)

The particle diagram above shows the system represented by the equation 2X(g)+Y2(g)⇄2XY(g) . Which of the following explains whether the particle diagram indicates that the system is at equilibrium?

A. The particle diagram does not indicate that the system is at equilibrium because it shows the system only at one point in time.

Which of the following best explains what the particle diagram is able to show about the entropy change for the dissolution of CuCl(s) in pure water?

A. The particle diagram shows that the dissociation of CuCl(s) into ions contributes to an increase in the entropy for the dissolution.

Which of the following best explains whether or not the particle diagram can predict the relative value of the enthalpy change for the dissolution of CuCl(s) ?

A. The value of the enthalpy change for the dissolution of CuCl(s) cannot be predicted from the particle diagram because it fails to illustrate the amount of energy required to overcome the forces between solute particles and between solvent particles.

Cu2+(aq) absorbs a certain frequency of visible light. Absorbance was measured for three saturated solutions of Cu(OH)2, each at a different pH at 298K. Based on the data recorded in the table above, which of the following conclusions about the effect of pH on the solubility of Cu(OH)2 can be made?

A. When the concentration of H+ ions is increased, the solubility of Cu(OH)2 increases.

At a certain temperature, SO2(g) and O2(g) react to produce SO3(g) according to the chemical equation shown above. An evacuated rigid vessel is originally filled with SO2(g) and O2(g), each with a partial pressure of 1atm. Which of the following is closest to the partial pressure of O2(g) after the system has reached equilibrium, and why?

B. 0.5atm; because Kp is very large, nearly all the SO2(g) is consumed before the system reaches equilibrium, but an excess amount of O2(g) remains at equilibrium.

The equilibrium in a saturated solution of Ca(OH)2 is represented above. In an experiment, a student places 5.0g of Ca(OH)2(s) into 100.0mL of distilled water and stirs the mixture. How would the results be affected if the student repeats the experiment but this time places 5.0g of Ca(OH)2(s) into 100.0mL of 0.0010MNaOH(aq) instead of distilled water?

B. Less solid will dissolve, because the larger value of [OH−] will cause the equilibrium position to lie farther to the left.

Which of the following changes to the particle diagram will best represent the effect of adding 1.0mL of 4MNaCl to the solution?

B. Some of the Cu+ and Cl− ions combine to form CuCl(s) because the molar solubility will be lower than 4×10−4M

A student poured 10mL of CoCl2(aq) into a test tube and added a few drops of concentrated HCl, which resulted in a deep-blue solution. The reaction that occurred is represented by the chemical equation shown above. Then, the student placed the test tube inside a beaker that contained ice and water for about five minutes. Which of the following describes what the student most likely observed next, and why?

B. The color of the solution changed from blue to pink, because cooling caused the equilibrium to shift to form the pink-colored Co(H2O)62+.

The equilibrium reaction in 0.100M HBrO(aq) at equilibrium is represented by the equation above. Based on the magnitude of the equilibrium constant, which of the following correctly compares the equilibrium concentrations of substances involved in the reaction, and why?

B. The equilibrium concentration of BrO− will be much smaller than the equilibrium concentration of HBrO, because Keq<<1

For which of the following salts would the relationship between molar solubility, s, in mol/L, and the value of Ksp be represented by the equation Ksp=4s3

C. Ag2SO4

CaF2(s) dissolves in water according to the equation CaF2(s)⇄Ca2+(aq)+2 F−(aq). The value of Ksp for the dissolution is 3.5×10−11. A student measures the concentration of Ca2+ ions in a saturated solution of CaF2 at various pH values and uses those values to generate the graph above. Based on the data, which of the following observations about the solubility of CaF2 is most valid?

C. It is higher at a lower pH; there are more H+ ions in solution at low pH, so HF forms and shifts the equilibrium reaction above to the right.

In an experiment involving the reaction shown above, a sample of pure HI was placed inside a rigid container at a certain temperature. The table above provides the initial and equilibrium concentrations for some of the substances in the reaction. Based on the data, which of the following is the value of the equilibrium constant (Keq) for the reaction, and why?

C. Keq=1.6×10−2, because [I2]eq=[H2]eq

Which of the following indicates the equilibrium value of PCl2 and the approximate value of the equilibrium constant Kp ?

C. PCl2=0.20atm and Kp=20.

A saturated solution of Hg2I2 is at equilibrium at 25°C as represented by the equation above. If [I−]=4.6×10−10 M at equilibrium, which of the following gives the correct molar solubility, S, and Ksp for Hg2I2 ?

C. S=2.3×10−10 M; Ksp=(2.3×10−10)(4.6×10−10)2

The dissolution of AgI is represented above. Which of the following shows the mathematical relationship between the molar solubility, S, of AgI and the Ksp at 298K?

C. S=√8.3×10−17 mol/L

The formation of FeSCN2+ in an aqueous solution is represented by the chemical equilibrium shown above. A light red-brown solution is prepared combining 12.50mL of 0.5MFe(NO3)3 , 0.5mL of 0.002MKSCN, and 37.0mL of water that had been slightly acidified. If an additional 1.0mL of 0.5MFe(NO3)3 is added, which of the following predicts and explains correctly whether the darkness of the color of the solution will change?

C. The color of the solution will darken because the equilibrium will favor the formation of more FeSCN2+

The particle diagrams above show the changes that occurred after an equimolecular mixture of X(g) and Y(g) was placed inside a rigid container at constant temperature. Which of the following statements is be best supported by the particle diagrams?

C. The forward reaction has a faster rate than the reverse reaction between 0s and 300s because more products were being formed.

The dissolution of solid AgCN is represented by the chemical equation above. In pure water, the equilibrium concentration of Ag+ ions in a saturated solution is 7.7×10−9M. If a small amount of solid NaCN is added to the saturated AgCN solution, which of the following would be observed?

C. The molar solubility of AgCN becomes smaller than 7.7×10−9M and some AgCN precipitates.

The chemical reaction shown above took place inside a rigid container at constant temperature. The table provides the concentrations of reactants and products at some point during the reaction. Based on this information, which of the following explains whether or not the reaction has reached equilibrium, and why?

C. The reaction is not at equilibrium because Qc<Kc; the forward reaction is favored in order to form more XY.

A sample of pure NO2(g) in a sealed tube at 20°C is placed in a temperature bath at 30°C. Observations of changes in the color, pressure, and mass of the mixture are recorded as a function of time. Which of the following is an observation that would best support the claim that the reaction represented above has reached equilibrium at 30°C?

C. The total pressure of the system decreases then reaches a constant value because at equilibrium the amounts of reactant and product no longer change.

Shown above are a chemical equation that represents the dissolution of PbBr2 in pure water, a table of the changes in some thermodynamic properties for the process, and a particle diagram. Which of the following explains which relative change in a thermodynamic property is best illustrated by the particle diagram?

C. The very small amount of Pb2+ and Br− ions illustrates that ΔG°>0 because the dissolution of PbBr2 is not a favorable process.

The diagram above represents the equilibrium between two isomers of 2-butene. The equilibrium constant, Kc, is 1.2 at a certain temperature. Two identical vessels each contain an equilibrium mixture of the two gases at that temperature. The concentration of cis‑2‑butene in the second vessel is twice the concentration in the first vessel. What is the concentration of trans‑2‑butene in the second vessel compared to that in the first vessel?

C. Twice the concentration of that in the first vessel

A sample of acetone is placed into a container. The container is sealed and attached to a pressure sensor, as shown in the diagram above. The container is allowed to sit on the lab table for a few minutes as the pressure in the container is monitored at regular intervals. At the end of 2.00 minutes, some acetone liquid remains in the container. Which of the following best explains the pressure data presented in the table above?

C. The acetone vaporizes from the liquid at a constant rate and the rate of condensation increases until it becomes equal to the rate of evaporation and the pressure stays constant.

When AgCl(s) is placed in water, it dissolves according to the chemical equation above. The particle diagram above was proposed to represent an aqueous solution in which AgCl(s) is in equilibrium with its ions. Which of the following best explains whether or not the diagram provides a good representation of this dynamic equilibrium at the microscopic level?

D. It is not a good representation because it does not illustrate the dynamic equilibrium in which the rates of the forward and reverse reactions are equal.

A student prepared a saturated aqueous solution of Mg(OH)2 and measured its pH, as shown in Figure 1 above. Then the student added a few drops of an unknown solution to the test tube and observed cloudiness in the solutions as shown in Figure 2. On the basis of this information and the equilibrium represented above, which of the following is most likely the identity of the reagent added from the dropper?

D. KOH(aq)

Based on the information given above, which of the following is the expression for Keq for the reaction that occurs when a 0.1MAgNO3(aq) is added to a saturated solution of PbCl2(aq), as represented by the following chemical equation?

D. Keq=K1/(K2)2

The table lists the initial concentrations of each substance in the system represented by the equation above at a given temperature. Which of the following best predicts what will occur as the system approaches equilibrium?

D. The rate of the reverse reaction will be greater than the rate of the forward reaction and additional CH3OH(g) will be consumed because Kc<Qc.

In a large reaction vessel at a constant temperature, nitrogen dioxide and dinitrogen tetroxide are in a state of dynamic equilibrium, as represented by the chemical equations shown above. The equilibrium constants for the reactions are K1 and K2. Which of the following quantities can most easily be used to find the value of K2?

D. The value of K1

A 0.10mol sample of solid zinc was added to 500.0mL of 1.0M Cu(NO3)2(aq). After the mixture sits overnight, which of the following best describes what was most likely observed and measured the next morning and why?

D. Virtually all of the Zn(s) will have disappeared and Cu(s) will have appeared in the beaker, because the reaction went almost to completion at equilibrium due to the very large Keq.

The graph above represents the data collected under certain conditions for the decomposition of N2O4(g) according to the chemical equation above. Based on the graph, at approximately which time is equilibrium established?

D. At time D, because there are no observable changes in [NO2] and [N2O4].