AP CHEM - Unit 7 MCQ Practice

Which of the following shows the relationship between K1 and K2 in the reactions represented above?

K2 = 1/(K1)^2

Reaction 1:CO(g)+3H2(g)⇄CH4(g)+H2O(g)CO(g)+3H2(g)⇄CH4(g)+H2O(g)K1=[CH4][H2O][CO][H2]3K1=[CH4][H2O][CO][H2]3 Reaction 2:CO2(g)+H2(g)⇄CO(g)+H2O(g)CO2(g)+H2(g)⇄CO(g)+H2O(g)K2=[CO][H2O][CO2][H2]K2=[CO][H2O][CO2][H2] Reaction 3:CH4(g)+2H2O(g)⇄CO2(g)+4H2(g)CH4(g)+2H2O(g)⇄CO2(g)+4H2(g)K3=? 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

Fe3+(aq)Colorless+ SCN−(aq)Colorless⇄ FeSCN2+(aq)RedFe3+(aq) When colorless solutions containing Fe3+(aq) ions and SCN−(aq) ions are combined, a deep-red complex ion, FeSCN2+(aq) 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(s) results in the red color of the solution becoming deeper?

The added KSCN(s) dissolves, causing the reaction system to respond by producing more product to partially consume SCN- (aq) and reduce its concentration.

N2(g)+3H2(g)⇄2NH3(g) A 2.0L reaction vessel contains an equilibrium mixture of the system represented above. The partial pressures of the components of the mixture at equilibrium are listed in the table below.

1.00 atm < P total < 2.00 atm

COCl2(g) ⇄ CO(g) + Cl2(g) COCl2(g) decomposes according to the equation above. When pure COCl2(g) is injected into a rigid, previously evacuated flask at 690 K, the pressure in the flask is initially 1.0 atm. After the reaction reaches 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?

0.050

X2(g)+Y2(g)⇄2XY(g)Kc=3.0 A mixture of X2(g), Y2(g), and XY(g) is placed in a previously evacuated, rigid container and allowed to reach equilibrium at a constant temperature, as shown above. Which of the following sets of initial concentrations would lead to the formation of more product as the system moves toward equilibrium?

0.30, M 0.30 M, 0.90 M

H2(g) + Br2(g) ⇄ 2HBr(g) At a certain temperature, the value of the equilibrium constant, K, for the reaction represented above is 2.0 x 105. What is the value of K for the reverse reaction at the same temperature?

5.0 x 10-6

NH3(g) 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(g) in the mixture after equilibrium is reestablished?

Adding some N2(g)

A sample of N2O4(g) is placed into an evacuated container at 373K and allowed to undergo the reversible reaction N2O4(g)⇄2NO2(g). The concentration of each species is measured over time, and the data are used to make the graph shown above. Which of the following identifies when equilibrium is first reached and provides a correct explanation?

At 60 seconds, because [NO2] and [N2O4] remain constant, indicating that the forward and reverse reaction rates are equal.

A 0.10 mol sample of each of the four species in the reaction represented above is injected into a rigid, previously evacuated 1.0 L container. Which of the following species will have the highest concentration when the system reaches equilibrium?

H2S(g)

CaCO3(s) ⇄ CaO(s) + CO2(g) ΔH° = 178 kJ/molrxn The reaction system represented above is at equilibrium. Which of the following will decrease the amount of CaO(s) in the system?

Lowering the temperature of the system

CO(g)+3H2(g)⇄CH4(g)+H2O(g)Kp=66 at 500°C At a certain time, the partial pressure of the gases in the reaction mixture represented above had the values shown in the table below. Based on the information above, which of the following occurred as the reaction mixture moved toward equilibrium?

More CH4(g) was produced because the rate of the forward reaction was higher than the rate of the reverse reaction.

H2(g) + I2(g) ⇌ 2 HI(g) Kc = 50. at 600°C Equimolar samples of each of three gases, H2(g), I2(g), and HI(g) , are introduced into a 3.0 L container that is heated to 600°C. According to the information above, which of the following will occur as the system approaches equilibrium?

More HI(g) will be produced because Q < Kc .

H2(g) + I2(g) ⇄ 2 HI(g) At 450oC, 2.0 moles each of H2(g), I2(g), and HI(g) are combined in a 1.0 L rigid container. The value of Kc at 450oC is 50. Which of the following will occur as the system moves toward equilibrium?

More HI(g) will form.

For which of the equilibrium systems represented below will the amount of product(s) at equilibrium increase if the volume of the reaction vessel is increased at a constant temperature?

PCl5(g) ⇄ PCl3(g) + Cl2(g)

2NO(g)+Br2(g)⇄2NOBr(g) Kp=(PNOBr)2(PNO)2(PBr2)=28 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/(10.0)^2(2.0) > Kp and equilibrium will be approached by consuming NOBr because the reverse reaction is faster than the forward reaction.

2NO(g)+Cl2(g)⇄2NOCl(g) Kc=2000 A mixture of NO(g) and Cl2(g) is placed in a previously evacuated container and allowed to reach equilibrium according to the chemical equation shown above. When the system reaches equilibrium, the reactants and products have the concentrations listed in the following table. 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 table above shows data for two reactions carried out in two separate evacuated 1.0-liter rigid containers at constant temperature of 298K. To each container 0.50mol of the appropriate reactants was added, and the reaction was allowed to reach equilibrium. Based on this information, which of the following correctly compares the relative concentrations of BrCl and NO present inside their respective containers at equilibrium?

[BrCl]eq > [NO]eq because the much larger [K]eq for reaction 1 means that a much higher concentration of products will be present at equilibrium for reaction 1 compared with reaction 2.

CO(g) + 2 H2(g) ⇄ CH3OH(g) ΔH < 0 The synthesis of CH3OH(g) from CO(g) and H2(g) is represented by the equation above. The value of Kc for the reaction at 483 K is 14.5. A 1.0 mol sample of CO(g) and a 1.0 mol sample of H2(g) are pumped into a rigid, previously evacuated 2.0 L reaction vessel at 483 K. Which of the following is true at equilibrium?

[H2] < [CO]

2NO2(g)⇄N2O4(g)Kc=200 The equilibrium system shown above is represented in the diagram below in which each molecule represents one mole of the substance in a 100.L container at a constant temperature. Additional N2O4(g) is added to the container and allowed to reestablish equilibrium. Which of the following best represents the system after the equilibrium has been reestablished?

the one with 5 molecules

N2O5(g) ⇄ 2 NO2(g) + ½ O2(g) The equilibrium constant for the gas phase reaction above is 95 at 25°C. What is the value of the equilibrium constant for the following reaction at 25°C? O2(g) + 4 NO2(g) ⇄ 2 N2O5(g)

1/(95)^2

ICl(g)⇄12I2(g)+12Cl2(g)Keq=0.1 Based on the information above, what is the value of Keq for the reaction represented below? I2(g)+Cl2(g)⇄2ICl(g)

100

2 NO2(g) ⇄ N2O4(g) dark brown colorless The dimerization of NO2(g) , an exothermic process, is represented by the equation above. A 0.0300 mol sample of NO2(g) is placed in a rigid 1.00 L reaction vessel and allowed to reach equilibrium at a certain temperature. What is the value of Kc at this temperature if 0.00500 mol of N2O4(g) is present at equilibrium?

12.5

CO(g) + 2 H2(g) ⇄ CH3OH(g) ΔH < 0 The synthesis of CH3OH(g) from CO(g) and H2(g) is represented by the equation above. The value of Kc for the reaction at 483 K is 14.5. A mixture of CO(g) and H2(g) is pumped into a previously evacuated 2.0 L reaction vessel. The total pressure of the reaction system is 1.2 atm at equilibrium. What will be the total equilibrium pressure of the system if the volume of the reaction vessel is reduced to 1.0 L at constant temperature?

Greater than 1.2 atm but less than 2.4 atm

2HI(g)⇄H2(g)+I2(g) Kp=PH2PI2P2HI=0.00162 The decomposition of HI(g) at 298K is represented by the equilibrium equation above. When 100.torr of HI(g) is added to a previously evacuated, rigid container and allowed to reach equilibrium, the partial pressure of I2(g) is approximately 3.7torr. If the initial pressure of HI(g) is increased to 200.torr and the process is repeated at the same temperature, which of the following correctly predicts the equilibrium partial pressure of I2(g), and why?

PI2 = 7.4 torr, because it is directly proportional to the initial pressure of HI.

Cl2(aq)+2H2O(l)⇄H3O+(aq)+Cl−(aq)+HOCl(aq) Kc=[H3O+][Cl−][HOCl][Cl2]=4.8×10−4 The equilibrium reaction between Cl2(aq) and H2O(l) 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= Kc/4, and the rate of the forward reaction will be greater than the rate of the reverse reaction.

A cylinder with a moveable piston is completely filled with a small amount (100 millimoles) of liquid water at a pressure of 1.0atm and a temperature of 80∘C. All the air in the cylinder is excluded. The cylinder is placed in a water bath held at 80∘C80∘C. The piston is slowly moved out to expand the volume of the cylinder to 20L as the pressure inside the cylinder is monitored. A plot of the pressure versus volume for the system is shown in the figure above. Which of the following statements most closely indicates, with justification, the region of the curve where the equilibrium represented below occurs?

Region B, because the pressure inside the cylinder is equal to the vapor pressure of water at 80∘C when both liquid and gas phases are present.

3 O2(g) ⇄ 2O3(g) Kc = 1.8 × 10−56 at 570 K For the system represented above, [O2] and [O3] initially are 0.150 mol/L and 2.5 mol/L respectively. Which of the following best predicts what will occur as the system approaches equilibrium at 570 K?

The amount of O3(g) will decrease, because Q > Kc.

2 SO3(g) ⇄ 2 SO2(g) + O2(g) After the equilibrium represented above is established, some pure O2(g) is injected into the reaction vessel at constant temperature. After equilibrium is reestablished, which of the following has a lower value compared to its value at the original equilibrium?

The amount of SO2(g) in the reaction vessel

X(g)+Y(g)⇄XY(g) The particle diagram above illustrates the changes that take place when X(g) and Y(g) are placed inside a rigid container at constant temperature. Which of the following is a characteristic of a system at equilibrium that is best represented by the particle diagram?

The particle diagram shows that after 200s there are no observable changes in the amounts of reactants and products, which is a characteristic of a system at equilibrium.

H2(g)+I2(g)⇄2HI(g) Hydrogen gas reacts with iodine gas at constant temperature in a sealed rigid container. The gases are allowed to reach equilibrium according to the equation above. Which of the following best describes what will happen to the reaction immediately after additional iodine gas is added to the system?

The rate of the forward reaction becomes greater than the rate of the reverse reaction.

2X(g)+Y2(g)⇄2XY(g) 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 than the rate of the reverse reaction.

H2 gas and N2 gas were placed in a rigid vessel and allowed to reach equilibrium in the presence of a catalyst according to the following equation. 3 H2(g) + N2(g) ⇄ 2 NH3(g) ΔHo = -92 kJ/molrxn The diagram below shows how the concentrations of H2 , N2 , and NH3 in this system changed over time. Which of the following was true for the system between time t1 and time t2?

The rates of the forward and reverse reactions were equal.

X(g)+Y(g)⇄XY(g) In an experiment, X(g)X(g) and Y(g)Y(g) 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 of X and XY remained constant.

2 XY(g) ⇄ X2(g) + Y2(g) Kp = 230 A certain gas, XY(g), decomposes as represented by the equation above. A sample of each of the three gases is put in a previously evacuated container. The initial partial pressures of the gases are shown in the table below. The temperature of the reaction mixture is held constant. In which direction will the reaction proceed?

The reaction will form more reactant.

2A(g)+B(g)⇄2C(g)\ A(g)and B(g) react to form C(g), according to the balanced equation above. In an experiment, a previously evacuated rigid vessel is charged with A(g), B(g), and C(g), each with a concentration of 0.0100M. The following table shows the concentrations of the gases at equilibrium at a particular temperature. If the experiment is repeated at a higher temperature at which Kc is larger, which of the following best describes the effect of the temperature change on the concentrations of the gases at equilibrium?

There will be a decrease in [A]eq that will be two times the decrease in [B}eq because AA and BB react in a 2-to-1 ratio.

A 2.0 mol sample of CO(g) and a 2.0 mol sample of H2O(g) 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]

The diagram above represents the equilibrium between the two isomers of C2H2Cl2, and the table provides the data collected in an experiment to determine its equilibrium constant, KcKc, at 490K. In a second experiment done at the same temperature, [Z]eq≈1.0 M[Z]eq≈1.0 M. Which of the following is the approximate equilibrium concentration of YY in the second experiment, and why?

[Y]eq = 1.5 M because the ratio [Z]eq/[Y]eq should remain constant when the reaction is done at the same temperature.

A mixture of NO2(g) and N2O4(g) is placed in a glass tube and allowed to reach equilibrium at 70°C, as represented above. If PN204 is 1.33 atm when the system is at equilibrium at 70°C, what is PNO2

2.0 atm

CO(g) + 2 H2(g) ⇄ CH3OH(g) Δ H < 0 The synthesis of CH3OH(g) from CO(g) and H2(g) is represented by the equation above. The value of Kc for the reaction at 483 K is 14.5. Which of the following explains the effect on the equilibrium constant, Kc, when the temperature of the reaction system is increased to 650 K?

Kc will decrease because the reaction is exothermic.

2 BaO2(s) ⇄ 2 BaO(s) + O2(g) ΔH°= 162 kJ/molrxn A sealed rigid vessel contains BaO2(s) in equilibrium with BaO(s) and O2(g) as represented by the equation above. Which of the following changes will increase the amount of BaO2(s) in the vessel?

Lowering the temperature

X(g) + 2 Q(g) ⇄ R(g) + Z(g) Kc = 1.3 × 105 at 50°C A 1.0 mol sample of X(g) and a 1.0 mol sample of Q(g) 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]

Refer to the following. PCl5(g) ⇄ PCl3(g) + Cl2(g) PCl5(g) decomposes into PCl3(g) and Cl2(g) according to the equation above. A pure sample of PCl5(g) is placed in a rigid, evacuated 1.00 L container. The initial pressure of the PCl5(g) is 1.00 atm. The temperature is held constant until the PCl5(g) reaches equilibrium with its decomposition products. The figures below show the initial and equilibrium conditions of the system. Additional Cl2(g) is injected into the system at equilibrium. Which of the following graphs best shows the rate of the reverse reaction as a function of time? (Assume that the time for injection and mixing of the additional Cl2(g) is negligible.)

the one with the highest spike