Unit 7
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.
When colorless solutions containing Fe3+ ions and SCN- 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 results in the red color of the solution becoming deeper?
C. The added KSCN(s)dissolves, causing the reaction system to respond by producing more product to partially consume SCN−(aq) and reduce its concentration.
In 1.0 M HCl is nearly 100 percent dissociated, as represented by the equation above. Which of the following best helps to explain why, in 0.01MHCN HCN is dissociated?
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).
Given the value of the equilibrium constants K1 and K2 for the reactions represented above, what is the value of the equilibrium constant, K3, for the following reaction?
A. 1 x 10^130
2H2S(g) + CH4 (G) -> CS2(g) + 4H2 Kc = 3.4x10^-4 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
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 K?
A. K5 = K1 x K3 / K4
Based on the Ksp values in the table above, a saturated solution of which of the following compounds has the highest [Cl-]
A. PbCl2
Reaction 1: NO3(g)+NO2(g)⇄N2O5(g) K=2.6×10−11 In the atmosphere, small water droplets are suspended in the air, forming an aerosol. N2O5(g) can form HNO3(aq) under these conditions, as shown in reaction 2, represented below. Reaction 2:N2O5(g)+H2O(l)→2HNO3(aq) Which of the following predicts the effect that the formation of HNO3(aq) will have on the equilibrium shown in reaction 1, and why?
A. The equilibrium of reaction 1 will shift toward the formation of more product, because N2O5(g)N2O5(g) is removed when it reacts to form HNO3(aq)HNO3(aq).
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? X(g)+Y(g)⇄XY(g)
C 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.
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∘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? 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.
The dissolution of calcium fluoride is represented by the equilibrium system above at 25°C. The F- ion is produced when the weak acid HF dissociates. If solid calcium fluoride is added to equal volumes of the following solutions at 25°C, in which solution will the most calcium fluoride dissolve?
B) 1MHNO3(aq)\
COCl2(g) 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 reaches equilibrium at 690 K, the total pressure in the flask is 1.2 atm. What is the value of K, for the reaction at 690 K?
B. 0.050
HgO + H2O <-> HgI4^2- + 2OH- Consider the equilibrium above. Which of the following changes will increase the concentration of HgI2-?
B. Adding 6M HNO3
For the reaction represented above, the value of the equilibrium constant, K ̧, is 240 at 25°C. From this information, correct deductions about the reaction at 25°C include which of the following?
B. II only
2NO + O2 <-> 2NO2 Which of the following changes alone would cause a decrease in the value of Keq for the reaction represented above?
B. Increasing the temperature
An equimolar mixture of X(g) and 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 300s?
B. It is not possible to determine that the system has reached equilibrium by 300s because the amounts of X, Y, and XY have continued to change.
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
The equilibrium constants for the dissolution (Ksp) of various substances in aqueous solution at 25°C are listed in the table above. Which of the following provides a correct comparison of the molar solubilities (S) of some of these substances based on their Ksp ?
B. The molar solubilities for CuCN and NiCO3 are calculated using S=√Ksp and CuCN has a lower molar solubility than NiCO3..
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? MgCO3(s)⇄Mg2+(aq)+CO32−(aq)
B. The molar solubility of MgCO3MgCO3 increases with increasing acidity (lower pH).
In an experiment, X(g) and 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? X(g)+Y(g)⇄XY(g)
B. The reaction reached equilibrium between 75 minutes and 155 minutes after the reactants were combined because the concentrations of X and XYremained constant.
A certain gas, XY 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 opposite. The temperature of the reaction mixture is held constant. In which direction will the reaction proceed?
B. The reaction will form more reactant
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]
SubstanceYZInitial concentration (M)2.00.0Equilibrium concentration (M)1.20.80 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, Kc, at 490K. In a second experiment done at the same temperature, [Z]eq≈1.0 M. Which of the following is the approximate equilibrium concentration of Y in the second experiment, and why?
B. [Y]eq≈1.5 M because the ratio [Z]eq[Y]eq should remain constant when the reaction is done at the same temperature.
The reaction system represented above is at equilibrium. Which of the following will decrease the amount of CaO(s) in the system?
B. lowering the temperature of the reaction
A student mixes dilute AgNO3(aq) with excess NaCl to form AgCl(s), as represented by the net ionic equation above. Which of the diagrams below best represents the ions that are present in the significant concentration in the solution?
C. (2 NO3-, 2 Cl-, 4 Na+)
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 condition of the system. As the reaction progresses toward equilibrium, the rate of the forward reaction Which of the following statements about Kp, the equilibrium constant for the reaction, is correct?
C. Decreases to become a constant nonzero rate at equilibrium. B. Kp < 1
Which of the following changes to the equilibrium system represented above will increase the quantity of HI in the equilibrium mixture?
C. I and II only
The synthesis of CH3OH from CO and H2 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?
C. Kc will decrease because the reaction is exothermic.
a. 1.0 L solution of AgNO3 of and Pb(NO3)2 has a Ag+ concentration of 0.02M and a Pb2+ concentration of 0.0010 M. A 0.0010 mol sample of K2SO4 is added to the solution. Based on the information in the table above, which of the following will occur?
C. Only PbSO4 will precipitate.
Reaction 1:HOCl(aq)+H2O(l)⇄H3O+(aq)+OCl−(aq)K1=[H3O+][OCl−][HOCl]Reaction 2:2H2O(l)⇄H3O+(aq)+OH−(aq)K2=[H3O+][OH−]Reaction 3:OCl−(aq)+H2O(l)⇄HOCl(aq)+OH−(aq)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
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]eqbecause A and B react in a 2-to-1 ratio.
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?
C. [CO2] > [CO]
A 1.0 mol 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?
C. [R] = [Z] > [Q]
At a certain point in time, a 1.00 L rigid reaction vessel contains 1.5 mol of PCI 1.0 mol of Cl2(g), and 2.5 mol of PCl(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
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] = [NO], because equimolecular mixtures of the reactants were allowed to reach equilibrium at the same constant temperature.
CC. [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.
During the day, solar radiation is absorbed by NO3(g), resulting in its decomposition. Which of the following best explains whether the equilibrium concentration of N2O5(g) in the atmosphere in the daytime is different from that in the nighttime, and why?
CC. [N2O5] will be higher at night, because the decomposition of NO3(g) in the daytime will result in an increase in the rate of consumption of)N2O5(g) to reform NO3(g).
Ca(OH)2 (s) precipitates when a 1.0 g sample of CaC2(s) is added to 1.0 L of distilled water at room temperature. If a 0.064 g sample of CaC2 (s) (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)
D. Ca(OH)2 will not precipitate because Q < Ksp
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
High solubility of an ionic solid in water is favored by which of the following conditions?
D. II and III only
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? CO + 3H2
D. K3=1/K1×1/K2
For the system represented above, [O2] and [03] 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 will decrease because Q > Kc
The table above lists the equilibrium constants and changes in thermodynamic properties for the dissolution of FeCO, and MnCO, at 25°C. The two particle diagrams opposite represent saturated solutions of each compound at equilibrium. Which of the following explains which of the properties listed in the table is best represented by the particle diagram?
D. The particle diagrams best represent that the molar solubility is greater for FeCO3 compared to MnCO3.
Shown above is the chemical equation for the dissolution of the slightly soluble salt CuBr. Its Ksp value in water was experimentally determined. CuBr was found to be muc less soluble in a 0.001M NaBr solution than in pure water. Which of the following correctly explains the decrease in solubility of CuBr in 0.001 M NaBr.
D. The presence of additional Br ions already in the solution means equilibrium will be reached when much less CuBr has dissolved
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: Which of the following was true for the system between time t, and time t? More NH3 gas is added to the system at the time t2 while the temperature is held constant Which of the following will most likely occur?
D. The rates of the forward and reverse reactions were equal B. THe amount of N2 will decrease.
At night, an equilibrium reaction between two different nitrogen compounds generates N2O5 in the atmosphere, as represented below.A mixture of NO, and a ten-fold excess of NO, 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?
D. [N2O5]<<[NO2], because a small K value indicates that the formation of products is not favored at equilibrium
A sealed rigid vessel contains BaO2) in equilibrium with BaO) and O2(g) as represented by the equation above. Which of the following changes will increase the amount of BaO2 in the vessel?
D. lowering the temperature
What is the molar solubility in water of Ag2CrO4
E. (2x10^-12)^⅓
N2O5 ⇌ 2No2 + 1/2 O2 The equilibrium constant for the gas phase reaction above is 95 ar 25 C. What is the value of the equilibrium constant for the following reaction at 25C O2 + 4NO2 ⇌ 2 N2O5
E. 1/(95)^2
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?
E. 2NO2 <-> N2O4
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
When 4.00 mol each of X and Y 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 is produced. What is the value of the equilibrium constant, K?
E. 36
The value of Ksp for PbCl2 is 1.6 ×10-5. What is the lowest concentration of Cl-(aq) that would be needed to begin precipitation of PbCl2(s) in 0.010 M Pb(NO3)2 ?
E. 4.0x10^-2 M
Which of the following statements is true for the equilibrium vapor pressure of a liquid in a closed system?
E. It is independent of the volume of the vapor phase.
After the equilibrium represented above is established, some pure O2 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?
E. The amount of SO2(g) in the reaction vessel.
The figure above shows two closed containers. Each contains the same volume of acetone in equilibrium with its vapor at the same temperature. The vapor pressure of the acetone is
E. the same in both containers because the temperature is the same.
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?
D At 60 seconds, because [NO2][NO2] and [N2O4][N2O4] remain constant, indicating that the forward and reverse reaction rates are equal.
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? 2NO(g)+Br2(g)⇄2NOBr(g) Kp=(PNOBr)2(PNO)2(PBr2)=28 SubstanceInitial Partial Pressure (torr)NO10.Br22.0NOBr80.
D Q=(80.)2(10.)2(2.0)>KpQ=(80.)2(10.)2(2.0)>Kp and equilibrium will be approached by consuming NOBrNOBr because the reverse reaction is faster than the forward reaction.
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. SpeciesConcentration (M)NO(g)0.050Cl2(g)0.050NOCl(g)0.50 Which of the following is true if the volume of the container is decreased by one half? 2NO(g)+Cl2(g)⇄2NOCl(g)Kc=2000
D Q=1000Q=1000, and the reaction will proceed toward products.
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? Cl2(aq)+2H2O(l)⇄H3O+(aq)+Cl−(aq)+HOCl(aq) Kc=[H3O+][Cl−][HOCl][Cl2]=4.8×10−4
D Qc=Kc4Qc=Kc4, and the rate of the forward reaction will be greater than the rate of the reverse reaction.
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? Cl2(aq)+2H2O(l)⇄H3O+(aq)+Cl−(aq)+HOCl(aq) Kc=[H3O+][Cl−][HOCl][Cl2]=4.8×10−4
D Qc=Kc4Qc=Kc4, and the rate of the forward reaction will be greater than the rate of the reverse reaction. D. (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.
The chemical equation above represents the equilibrium that exists in a saturated solution of Ag2CO3. If S represents the molar solubility of Ag2CO3, which of the following mathematical expressions shows how to calculate S based on Ksp? Ag2CO3(s)⇄2Ag+(aq)+CO32−(aq)
D S=Ksp4−−−√3
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? 2X(g)+Y2(g)⇄2XY(g)
D The rate of the forward reaction is greater than the rate of the reverse reaction.
The student places the same mass of AgOH into 50.0mL of different solutions with specific pH values and measures the concentration of Ag+ ions in each solution after equilibrium is reached. Based on the data in the table, what can be concluded about the solubility of AgOH?
D, AgOH is less soluble at higher pH because higher concentrations of OH−(aq) shift the solubility equilibrium toward solid AgOH
In a saturated solution of Zn(OH)2 at 25°C, the value of [OH-] is 2.0 x 10-4 M. What is the value of the solubility-product constant, Ksp, for Zn(OH)2 at 25°C ?
D. 4.0 x 10^-18
According to the information about the dissolution of Ba(IO3)2(s) shown above, the correct value of S, the molar solubility of Ba(IO3)2(s), can be calculated using with of the following mathematical relationships? Ba(IO3)2(s) ⇄ Ba2+(aq) + 2 IO3−(aq) Ksp=4×10−9
D. 4S3=4×10−9 M
NH3(g) was synthesized at 200°C in the presence of a powdered Os 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?
D. Adding some N2
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 the 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?
a. The better particle diagram was drawn by Student 1 because when LiCl dissolves in water, it dissociates into Li+ and Cl− ions causing an increase in entropy.
At 298K, 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(s) 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?
c. The particle diagram is able to illustrate that entropy increases when NH4NO3(s) dissolves in water because the ions disperse in solution.
A saturated aqueous solution of CdF2 is prepared. The equilibrium in the solution is represented above. In the solution, [Cd2+]eq=0.0585M and [F−]eq=0.117M. Some 0.90MNaF 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? CdF2(s)⇄Cd2+(aq)+2F−(aq)
A. The molar solubility of CdF2CdF2 in pure water is 0.0585M, and adding NaF decreases this solubility because the equilibrium shifts to favor the precipitation of some CdF2.
The exothermic dissolution of Mg(OH)2, in water is represented by the equation above. sp The Ksp of Mg(OH)2 is 1.8 x 10-11. Which of the following changes will increase the solubility of Mg(OH)2 in an aqueous solution?
A. decreasing the pH
Shown above is information about the dissolution of AgCl(s) in water at 298K. 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 altered if the student mixed excess AgCl with tap water (in which [Cl−]=0.010M) instead of distilled water and the student did not account for the Cl− in the tap water? AgCl(s) ⇄ Ag+(aq)+Cl−(aq)Ksp=1.8×10−10
B The value obtained for KspKsp would be too small because less AgCl(s)AgCl(s) would dissolve because of the common ion effect due to the Cl−(aq)Cl−(aq) already in the water.
