ap chem 7.1-7.7 review

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?

A H2S(g)

H2CO3(aq)+NH3(aq)⇄NH4+(aq)+HCO3−(aq)H2CO3(aq)+NH3(aq)⇄NH4+(aq)+HCO3−(aq)K5=?K5=? 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 K5K5?

A K5=K1×K3/K4

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?

B The reaction will form more reactant.

2X(g) + Y(g) ⇄ 3Z(g) The reaction mixture represented above is at equilibrium at 298 K, and the molar concentrations are [X] = 2.0 M, [Y] = 0.5 M, and [Z] = 4.0 M. What is the value of the equilibrium constant for the reaction at 298 K ?

E 32

X(g) + Y(g) ⇄ 2Z(g) When 4.00 mol each of X(g) and Y(g) are placed in a 1.00 L vessel and allowed to react at constant temperature according to the equation above, 6.00 mol of Z(g) is produced. What is the value of the equilibrium constant, Kc ?

E 36

At night, an equilibrium reaction between two different nitrogen compounds generates N2O5 in the atmosphere, as represented below. Reaction 1: NO3(g) + NO2(g) ⇄ N2O5(g) K = 2.6×10−11 A mixture of NO3 and a ten-fold excess of NO2 are placed inside a rigid container at constant temperature and allowed to reach equilibrium. Which of the following provides a correct comparison of the equilibrium concentrations of these chemical species, and why?

[N2O5] << [NO2] because a small K value indicates that the formation of the products is not favored at equilibrium.

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?

B 0.050

Equimolar samples of CH3OH(l) and C2H5OH(l) are placed in separate, previously evacuated, rigid 2.0 L vessels. Each vessel is attached to a pressure gauge, and the temperatures are kept at 300 K. In both vessels, liquid is observed to remain present at the bottom of the container at all times. The change in pressure inside the vessel containing CH3OH(l) is shown below. The value of Kp for the evaporation of CH3OH(l) at 300 K is closest to

B 0.2

Kp = 3.0 at 70°C colorless brown 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 PN2O4 is 1.33 atm when the system is at equilibrium at 70°C, what is PNO2?

B 2.0 atm

Fe3+(aq) + SCN-(aq) ⇄ Fe(SCN)2+(aq) For the reaction represented above, the value of the equilibrium constant, Keq, is 240 at 25°C. From this information, correct deductions about the reaction at 25°C include which of the following? I. The reaction is quite rapid. II. The product is favored over the reactants at equilibrium. III. The reaction is endothermic.

B II only

An equimolar mixture of X(g)X(g) and Y(g)Y(g) is placed inside a rigid container at constant temperature. The particle diagram above represents the changes that occur over time. Based on the particle diagram, which of the following best predicts whether or not the system has reached equilibrium by 300s300s?

B It is not possible to determine that the system has reached equilibrium by 300s300s because the amounts of XX, YY, and XYXY have continued to change.

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. Which of the following statements about Kp, the equilibrium constant for the reaction, is correct?

B Kp < 1

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?

B More HI(g) will form.

In 1.0MHCl(aq), HCl is nearly 100 percent dissociated, as represented by the equation above. Which of the following best helps to explain why, in 0.01MHCN(aq), less than 1 percent of HCN is dissociated?HCl(aq)+H2O(l)⇄H3O+(aq)+Cl−(aq)

C The equilibrium constant for the dissociation of HCN(aq)HCN(aq) is much smaller than that for the dissociation of HCl(aq)HCl(aq).

X(g)+Y(g)⇄XY(g)X(g)+Y(g)⇄XY(g) The particle diagram above illustrates the changes that take place when X(g)X(g) and Y(g)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?

C The particle diagram shows that after 200s200s there are no observable changes in the amounts of reactants and products, which is a characteristic of a system at equilibrium.

PCl3(g) + Cl2(g) ⇄ PCl5(g) Kc = 6.5 At a certain point in time, a 1.00 L rigid reaction vessel contains 1.5 mol of PCl3(g), 1.0 mol of Cl2(g), and 2.5 mol of PCl5(g). Which of the following describes how the measured pressure in the reaction vessel will change and why it will change that way as the reaction system approaches equilibrium at constant temperature?

C The pressure will decrease because Q < Kc.

2A(g)+B(g)⇄2C(g)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?

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

A cylinder with a moveable piston is completely filled with a small amount (100 millimoles) of liquid water at a pressure of 1.0atm1.0atm and a temperature of 80∘C80∘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 20L20L 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? H2O(l)⇄H2O(g)H2O(l)⇄H2O(g)

B Region B, because the pressure inside the cylinder is equal to the vapor pressure of water at 80∘C80∘C when both liquid and gas phases are present.

X(g)+Y(g)⇄XY(g)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?

B The reaction reached equilibrium between 75 minutes and 155 minutes after the reactants were combined because the concentrations of XX and XYXY remained constant.

The diagram above represents the equilibrium between the two isomers of C2H2Cl2C2H2Cl2, and the table provides the data collected in an experiment to determine its equilibrium constant, KcKc, at 490K490K. 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?

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

The table above shows data for two reactions carried out in two separate evacuated 1.0-liter rigid containers at constant temperature of 298 K. To each container 0.50 mol 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?

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

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?

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

2HI(g)⇄H2(g)+I2(g) Kp=PH2PI2/PHI2=0.0016 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?

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

Reaction 1:HOCl(aq)+H2O(l)⇄H3O+(aq)+OCl−(aq)HOCl(aq)+H2O(l)⇄H3O+(aq)+OCl−(aq)K1=[H3O+][OCl−][HOCl]K1=[H3O+][OCl−][HOCl]Reaction 2:2H2O(l)⇄H3O+(aq)+OH−(aq)2H2O(l)⇄H3O+(aq)+OH−(aq)K2=[H3O+][OH−]K2=[H3O+][OH−]Reaction 3:OCl−(aq)+H2O(l)⇄HOCl(aq)+OH−(aq)OCl−(aq)+H2O(l)⇄HOCl(aq)+OH−(aq)K3=?K3=? Based on the equilibrium constants given above, which of the following gives the correct expression for the equilibrium constant for reaction 3?

A K3=K2/K1

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?

D 12.5

A sample of N2O4(g)N2O4(g) is placed into an evacuated container at 373K373K and allowed to undergo the reversible reaction N2O4(g)⇄2NO2(g)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?

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

4 HCl(g) + O2(g) ⇄ 2 Cl2(g) + 2 H2O(g) Equal numbers of moles of HCl and O2 in a closed system are allowed to reach equilibrium as represented by the equation above. Which of the following must be true at equilibrium? I. [HCI] must be less than [Cl2]. II. [O2] must be greater than [HCl]. III. [Cl2] must equal [H2O].

D II and III only

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]3Reaction 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=?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 K3K3 for reaction 3 at the same temperature?

D K3=1/K1×1/K2

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?

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

2X(g)+Y2(g)⇄2XY(g)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 ?

D The rate of the forward reaction is greater than the rate of the reverse reaction.

Ag+(aq)+2NH3(aq)⇄[Ag(NH3)2]+(aq)K=1×107Ag+(aq)+2NH3(aq)⇄[Ag(NH3)2]+(aq)K=1×107 Equal volumes of 0.1MAgNO3(aq)0.1MAgNO3(aq) and 0.4MNH3(aq)0.4MNH3(aq) are mixed and allowed to reach the equilibrium represented above. Which of the following correctly lists the equilibrium concentrations of the Ag+(aq)Ag+(aq), NH3(aq)NH3(aq), and [Ag(NH3)2]+(aq)[Ag(NH3)2]+(aq) in order from least to greatest?

D [Ag+]eq<[[Ag(NH3)2]]eq+<[NH3]eq

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?

B [H2] < [CO]