Chemistry Retake

The concentration of F−(aq) in drinking water that is considered to be ideal for promoting dental health is 4.0×10−5M. Based on the information above, the maximum concentration of Ca2+(aq) that can be present in drinking water without lowering the concentration of F−(aq) below the ideal level is closest to CaF2(s)⇄Ca2+(aq)+2 F−(aq) Ksp=4.0×10−11

0.025M

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

The value of Kp for the evaporation of CH3OH(l) at 300 K is closest to

0.2

2 S(s) + 2 O2(g) ⇄ 2 SO2(g) K1 = 2 x 10^105 2 SO2(g) + O2(g) ⇄ 2 SO3(g) K2 = 7 x 10^24 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? 2 S(s) + 3 O2(g) ⇄ 2 SO3(g) K3 = ?

1 x 10^130

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

Ge(g)+2Cl2(g)⇄GeCl4(g) The value of the equilibrium constant for the reaction represented above is 1×10101×1010. What is the value of the equilibrium constant for the following reaction? 2GeCl4(g)⇄2Ge(g)+4Cl2(g)

1×10^-20

N2O4(g)⇌2NO2(g) colorless brown Kp = 3.0 at 70°C 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?

2.0 atm

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 ?

36

X2(g)+Y2(g)⇄2XY(g)Kc=3.0X2+Y2⇄2XY Kc=3.0 A mixture of X2, 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?

A. X=.4, Y=.4, XY=.2

CaF2(s) ⇄ Ca2+(aq) + 2 F-(aq) ΔH>0 Dissolution of the slightly soluble salt CaF2 is shown by the equation above. Which of the following changes will decrease [Ca2+] in a saturated solution of CaF2 , and why? (Assume that after each change some CaF2(s) remains in contact with the solution.)

Adding NaF(s), because the reaction will proceed toward reactants

Equal volumes of 0.1 M AgNO3(aq) and 2.0 M NH3(aq) are mixed and the reactions represented above occur. Which Ag species will have the highest concentration in the equilibrium system shown below, and why?

Ag(NH3)2+(aq), because Keq3 = 1.6 x 107

The saturated CuSO4(aq)shown above is left uncovered on a lab bench at a constant temperature. As the solution evaporates, 1.0mL samples of the solution are removed every three days and the [SO42−] in the samples is measured. It is observed that the [SO42−] in the solution did not change over time. Which of the following best helps to explain the observation?

As water evaporates, more CuSO4(s) precipitates out of the solution in the beaker.

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.)

B. stable, goes up, comes a bit down

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)

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? The reaction is quite rapid. The product is favored over the reactants at equilibrium. The reaction is endothermic.

II only

Based on the information above, which of the following expressions represents the equilibrium constant, K, for the reaction represented by the equation below? La3+ + CO32− ⇄ LaCO3+

K = (K1)(Kw) / (Ka)

Which of the following shows the relationship between K1 and K2 in the reactions represented above? SO2 + 1/2O2 ⇄ SO3 K1 2SO3 ⇄ 2SO2 +O2

K2 = 1/(K1)^2

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? CO(g) + 2 H2(g) ⇄ CH3OH(g) Δ H < 0

Kc will decrease because the reaction is exothermic.

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? 2 BaO2(s) ⇄ 2 BaO(s) + O2(g) ΔH°= 162 kJ/molrxn

Lowering the temperature

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

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? H2(g) + I2(g) ⇌2 HI(g) Kc = 50. at 600°C

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.

N2O4(g)⇌2NO2(g) colorless brown Kp = 3.0 at 70°C 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. Which of the following best predicts how the partial pressures of the reacting species will be affected if a small amount of Ar(g) is added to the equilibrium mixture at constant volume?

No change will take place

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)

Equimolar samples of Pb(OH)2(s), PbI2(s), and PbF2(s) are placed in three separate beakers, each containing 250 mL of water at 25°C. After the solutions are stirred, solid remains in the bottom of each beaker. Based on the Ksp values for the compounds listed in the table above, a solution of which of the compounds will have the lowest [Pb2+] ?

Pb(OH)2(s)

Reaction A: 4 HCl(g) + O2(g) ⇄ 2 Cl2(g) + 2 H2O(g) Reaction B: N2O4(g) ⇄ 2 NO2(g) Reaction C: H2(g) + I2(g) ⇄ 2 HI(g) Reaction D: 2 NH3(g) ⇄ N2(g) + 3 H2(g) The reactions represented above are carried out in sealed, rigid containers and allowed to reach equilibrium. If the volume of each container is reduced from 1.0 L to 0.5 L at constant temperature, for which of the reactions will the amount of product(s) be increased?

Reaction A

3 O2(g) ⇄ 2 O3(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.

N2O4(g)⇌2NO2(g) colorless brown Kp = 3.0 at 70°C 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. Which of the following statements best helps to explain why the contents of the tube containing the equilibrium mixture turned a lighter color when the tube was placed into an ice bath?

The forward reaction is endothermic.

Cr2O72−(aq) + 3 H2O(l)⇌⇌2 CrO42−(aq) + 2 H3O+(aq) orange yellow The equilibrium system represented by the equation above initially contains equal concentrations of Cr2O72−(aq) and CrO42−(aq). Which of the following statements correctly predicts the result of adding a sample of 6.0 M NaOH(aq) to the system, and provides an explanation?

The mixture will become more yellow because OH−(aq) will shift the equilibrium toward products.

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.

Three saturated solutions (X, Y, and Z) are prepared at 25°C. Based on the information in the table above, which of the following lists the solutions in order of increasing [Ag+] ?

Z < X < Y

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]

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]

2 NO2(g) ⇄ N2O4(g) dark brown colorless The dimerization of NO2(g) , an exothermic process, is represented by the equation above. A mixture of NO2(g) and N2O4(g) is at equilibrium in a rigid reaction vessel. If the temperature of the mixture is decreased, then

[N2O4] will increase and the mixture will turn a lighter brown

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? X(g) + 2 Q(g) ⇄ R(g) + Z(g) Kc = 1.3 × 105 at 50°C

[R] = [Z] > [Q]

Li3N(s) + 2 H2(g) ⇄ LiNH2(s) + 2 LiH(s) ΔH° = -192 kJ/molrxn Because pure H2 is a hazardous substance, safer and more cost effective techniques to store it as a solid for shipping purposes have been developed. One such method is the reaction represented above, which occurs at 200°C. The amount of H2(g) present in a reaction mixture at equilibrium can be maximized by

increasing the temperature and decreasing the pressure by increasing the volume