Unit 7 Topic ?s

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=K2K1

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 0.0585M0.0585M, and adding NaFNaF decreases this solubility because the equilibrium shifts to favor the precipitation of some CdF2CdF2.

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 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 CuCNCuCN and NiCO3NiCO3 are calculated using S=Ksp−−−√S=Ksp and CuCNCuCN has a lower molar solubility than NiCO3NiCO3.

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 pHpH).

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.

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? 2HI(g)⇄H2(g)+I2(g) Kp=PH2PI2P2HI=0.0016

C PI2≈7.4 torrPI2≈7.4 torr, because it is directly proportional to the initial pressure of HIHI.

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 M4S3=4×10−9 M

A student investigates the effects of pH on the solubility of AgOH(s), which dissolves in water according to the equation AgOH(s)⇄Ag+(aq)+OH−(aq). The value for Ksp for AgOH is 2.0×10−8 at 298K. The student places the same mass of AgOH(s) 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 AgOHAgOH is less soluble at higher pHpH because higher concentrations of OH−(aq)OH−(aq) shift the solubility equilibrium toward solid AgOHAgOH.

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?

D Q=1000Q=1000, and the reaction will proceed toward products.

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 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.