Deck 5: Equilibrium

Question 1

In a pressure cooker,the boiling point of water is less than 100 ^$\omicron$ C.

Answer 1

False

Question 2

Estimate the enthalpy of vaporization of CCl₄ given that at 25 ^$\omicron$ C and 58 ^$\omicron$ C its vapor pressure is 107 and 405 Torr, respectively.Assume that the enthalpy of vaporization is independent of the temperature.

A) 486 J.mol^-1
B) 48.6 kJ.mol^-1
C) 142 kJ.mol^-1
D) 3.98 kJ.mol^-1
E) 33.1 kJ.mol^-1

Answer 2

33.1 kJ.mol^-1

Question 3

The phase diagram for a pure substance is shown below. What is the lowest temperature at which liquid can exist?

A) 400 K
B) 0 K
C) 200 K
D) 150 K
E) 250 K

Answer 3

C

Question 4

A plot of ln(vapor pressure) versus 1/T for methanol gives a straight line with an intercept of 13.6.The entropy of vaporization of methanol is

A) 611 J.mol^-1.K^-1.
B) 113 J.mol^-1.K^-1.
C) 1640 J.mol^-1.K^-1.
D) Not enough information given to calculate.
E) 13.6 J.mol^-1.K^-1.

Question 5

The phase diagram for a pure compound is given below .All of the following could have a similar phase diagram except

A) methanol
B) carbon dioxide
C) benzene
D) carbon tetrachloride
E) water

Question 6

The vapor pressure of water above 40 mL of water in a 100 mL container is 23.8 Torr at 25 ^$\omicron$ C .What is the vapor pressure of the water if the volume of the container is changed to 50 mL?

A) About 25 Torr
B) About 20 Torr
C) 23.8 Torr
D) 47.6 Torr
E) 11.9 Torr

Question 7

Estimate the enthalpy of vaporization of water given that at 25 ^$\omicron$ C and 35F ^$\omicron$ C its vapor pressure is 23.8 and 42 Torr, respectively.Assume that the enthalpy of vaporization is independent of the temperature.

A) 415 J.mol^-1
B) 221 kJ.mol^-1
C) 41.5 kJ.mol^-1
D) 5.21 kJ.mol^-1
E) 43.4 kJ.mol^-1

Question 8

In a closed vessel containing water the pressure is 18 Torr .If more water is added to the vessel,The pressure

A) remains the same.
B) becomes larger.
C) becomes smaller.

Question 9

The vapor pressure of benzene at 25 ^$\omicron$ C is 94.6 Torr and its enthalpy of vaporization is 30.8 kJ.mol^-1 . Estimate the normal boiling point of benzene.Assume the enthalpy of vaporization is independent of temperature.

A) 640 K
B) 358 K
C) 470 K
D) 624 K
E) Not enough information given.

Question 10

The vapor pressure of methanol at 25 ^$\omicron$ C is 123 Torr and its enthalpy of vaporization is 35.3 kJ.mol^-1 . Estimate the normal boiling point of methanol.Assume the enthalpy of vaporization is independent of temperature.

A) 450 K
B) 342 K
C) 315 K
D) 373 K
E) Not enough information given.

Question 11

A plot of ln(vapor pressure) versus 1/T for benzene gives a straight line with slope -3.70 * 10³ K.The enthalpy of vaporization of benzene is

A) 2.25 kJ.mol^-1.
B) Not enough information is given to permit the calculation.
C) 3.70 kJ.mol^-1.
D) 30.8 kJ.mol^-1.
E) 445 J.mol^-1.

Question 12

Why is the vapor pressure of cis-dibromoethene lower than the vapor pressure of trans-dibromoethene?

A) Ion-dipole forces
B) London forces
C) Hydrogen bonding
D) Ion-ion forces
E) Dipole-dipole forces

Question 13

A plot of ln(vapor pressure) versus 1/T for methanol gives a straight line with an intercept of 13.6.The enthalpy of vaporization of methanol is

A) 113 kJ.mol^-1.
B) 13.6 kJ.mol^-1.
C) 611 kJ.mol^-1.
D) 1.64 kJ.mol^-1.
E) Not enough information given to calculate.

Question 14

Which liquid would you expect to be the more volatile,CH₃CHO or CH₃OCH₃?

Question 15

What is the vapor pressure of carbon disulfide at its normal boiling point?

Question 16

Which of the following has the highest vapor pressure?

A) H₂O
B) CH₃CH₂OH
C) CH₃CH₂OCH₂CH₃
D) CH₃OH
E) CH₃CH₂COOH

Question 17

The vapor pressure of water at 37 ^$\omicron$ C is 47.1 Torr and its enthalpy of vaporization is 44.0 kJ.mol^-1 .Estimate the vapor pressure of water at 87 ^$\omicron$ C.Assume that the enthalpy of vaporization of water is independent of temperature.

A) 112 Torr
B) 256 Torr
C) 713 Torr
D) 52 Torr
E) 504 Torr

Question 18

Which of the following liquids freeze at a lower temperature when pressure is applied?

A) Water
B) Acetic acid
C) Benzene
D) Methanol
E) Carbon tetrachloride

Question 19

The phase diagram for a pure compound is shown below .The triple point occurs at

A) 50 atm and 200 K.
B) 0 atm and 200 K.
C) greater than 50 atm and greater than 200 K.
D) 320 atm and 250 K.
E) 200 atm and 400 K.

Question 20

the boiling point of water is higher in a pressure cooker than the normal boiling point?

Question 21

the triple point for water,4.6 Torr and 0.01 ^$\omicron$ C,varies depending on conditions?

Question 22

The phase diagram for a pure substance is given below. The substance is stored in a container at 150 atm at 25 ^$\omicron$ C.Describe what happens if the container is opened at 25 ^$\omicron$ C.

A) The liquid in the container freezes.
B) The solid in the container sublimes.
C) The solid in the container melts.
D) The vapor in the container escapes.
E) The liquid in the container vaporizes.

Question 23

For a one-component system, at the triple point

A) f = 3.
B) f = 2.
C) p = 1.
D) f = 0.
E) f = 1.

Question 24

The phase diagram for CO₂ is given below .
The triple point is at 5.1 atm and 217 K.
What happens if carbon dioxide at 50C and 25 atm is suddenly brought to 1 atm?

A) The liquid and solid are in equilibrium.
B) The solid melts.
C) The solid and vapor are in equilibrium.
D) The solid vaporizes.
E) The solid remains stable.

Question 25

The phase diagram for a pure substance is shown below. At 100 atm and 250 K,
The substance exists as

A) both vapor and liquid in equilibrium.
B) liquid.
C) both vapor and solid in equilibrium.
D) vapor.
E) solid.

Question 26

The phase diagram for a pure substance is given below .What is the critical temperature?

A) 0 K
B) 250 K
C) 300 K
D) 400 K
E) 200 K

Question 27

What is the highest temperature that the substance shown in the following phase diagram can exist as a liquid?

A) any temperature above 200 K
B) 200 K
C) 250 K
D) 350 K
E) 400 K

Question 28

When three phases are in mutual equilibrium,such as at the triple point of water,the degrees of freedom equal 0.

Question 29

The phase diagram for a pure substance is given below .
The solid sublimes

A) at 400 K and 200 atm.
B) at 200 K and 100 atm.
C) at 300 K and 100 atm.
D) at 300 K and 75 atm.
E) if warmed at any pressure below 50 atm.

Question 30

Consider the phase diagrams for water and carbon dioxide given in the text on page 315.Explain the following observations: A thin wire with weights attached is draped over a block of "dry ice," a second wire with weights is draped over a block of ice.The wire cuts through the ice but not through the "dry ice."

Question 31

The phase diagram for sulfur is given below. The number of phases that sulfur can exist in and the number of triple points,Respectively,Are

A) 3 and 2.
B) 3 and 3.
C) 4 and 2.
D) 3 and 1.
E) 4 and 3.

Question 32

Consider the phase diagram for sulfur in the text on page 316.Monoclinic sulfur is denser than rhombic sulfur.

Question 33

The phase diagram for a pure substance is shown below .What is the critical pressure?

A) 50 atm
B) 150 atm
C) 325 atm
D) Any pressure above 325 atm
E) 200 atm

Question 34

The phase diagram for sulfur is given below. Which of the following is true?

A) Sulfur has 2 triple points.
B) Monoclinic sulfur does not sublime.
C) Sulfur has 0 triple points.
D) Sulfur has 3 triple points.
E) Rhombic sulfur cannot be directly converted to liquid.

Question 35

The phase diagram for CO₂ is given below .The triple point is at 5.1 atm and 217 K.
What happens if CO₂(l)At 30 atm and 450 K is released into a room at 1 atm and 298 K?

A) The liquid vaporizes.
B) The liquid remains stable.
C) The liquid and vapor are in equilibrium.
D) The liquid and solid are in equilibrium.
E) The liquid freezes.

Question 36

Consider the phase diagrams for water and carbon dioxide given in the text on page 315.Explain the significance of the slopes of the solid-liquid lines.

Question 37

A gas is a form of matter that can be liquefied at any temperature by pressure alone.

Question 38

The phase diagram for a pure substance is given below. What pressure must be applied to liquefy a sample at 425 K?

A) 350 atm
B) The sample cannot be liquefied at 425 K.
C) 150 atm
D) 50 atm
E) 250 atm

Question 39

The phase diagram for sulfur is given below. At 424 K and 1300 atm,

A) rhombic sulfur, monoclinic sulfur, sulfur liquid, and sulfur gas exist in equilibrium.
B) only rhombic sulfur and sulfur gas exist in equilibrium.
C) rhombic sulfur, monoclinic sulfur, and liquid sulfur exist in equilibrium.
D) only rhombic sulfur is present.
E) only monoclinic sulfur is present.

Question 40

The phase diagram for carbon dioxide is given below. If the triple point is at 5.1 atm and 56C,
At 1 atm and room temperature

A) solid carbon dioxide is the stable phase.
B) liquid carbon dioxide is the stable phase.
C) gaseous carbon dioxide condenses.
D) gaseous carbon dioxide is the stable phase.
E) solid carbon dioxide melts.

Question 41

For AlF₃,the lattice enthalpy is 5220 kJ.mol^-1 and the enthalpy of solution is -27 kJ.mol^-1 at 25 ^$\omicron$ C.Calculate the enthalpy of hydration of AlF₃ at this temperature.

Question 42

The enthalpy of hydration of AgBr is -819 kJ.mol^-1 at 25 ^$\omicron$ C .Given that the hydration enthalpy of Br^- is -309 kJ.mol^-1,Calculate the enthalpy of hydration of Ag⁺ ions.

A) -410 kJ.mol^-1
B) -819 kJ.mol^-1
C) -1128 kJ.mol^-1
D) -309 kJ.mol^-1
E) -510 kJ?mol^?1

Question 43

Which of the following statements is true regarding solubility? Assume that the solute does not affect the solvent and we are dealing with dilute solutions.

A) We can expect substances with positive enthalpies of solution always to be soluble.
B) We can expect substances with positive enthalpies of solution always to be soluble only if the entropy of solution is negative.
C) All the other statements are false because the solute always affects the solvent resulting in a negative entropy of solution.
D) We can expect substances with negative enthalpies of solution always to be soluble.
E) We can expect substances with positive enthalpies of solution always to be soluble only if the entropy of solution is positive.

Question 44

Aqueous ammonia (28%)is 15.0 M and has a density of 0.90 g.mL^-1.Calculate the molality of ammonia in this solution.

Question 45

What is the molality of CrCl₃ in a solution prepared by dissolving 75.2 g of chromium(III) chloride hexahydrate in 250.0 g of water.

A) 0.282 m
B) 1.13 m
C) 7.60 m
D) 5.64 m
E) 1.90 m

Question 46

What is the molality of carbon tetrachloride in a solution of toluene,given that the mole fraction is 0.200?

Question 47

Benzene would likely dissolve which of the following substances?

A) Cl₂CCCl₂
B) NaCl
C) Na₂CO₃
D) Ca(HCO₃)₂
E) C₆H₁₂O₆

Question 48

Calculate the concentration of argon in lake water at 20?C .The partial pressure of argon is 0.0090 atm and Henrys constant is 0.0015 mol?L^?1?atm^?1.

A) 1.5 ? 10^?3 M
B) 9.0 ? 10^?3 M
C) 1.4 ? 10^?5 M
D) 6.0 M
E) 0.17 M

Question 49

For CaCl₂,the enthalpies of hydration and solution are -2337 and -81 kJ.mol^-1,respectively,at 25 ^$\omicron$ C.Calculate the lattice enthalpy of calcium chloride.

Question 50

Which of the following is likely to have the largest exothermic hydration enthalpy?

A) Sr²⁺
B) Na⁺
C) Mg²⁺
D) Ca²⁺
E) Li⁺

Question 51

If you wanted to study solutions of different concentrations at different temperatures,would you use molarity or molality as your measure of concentration? Why?

Question 52

Calculate the molality of ethanol in a solution of water,given that the mole fraction of ethanol is 0.300.

Question 53

For AgI, the lattice enthalpy is larger than the absolute value of the enthalpy of hydration.This means that for AgI

A) $\Delta$ H_sol is positive.
B) the solubility increases when the temperature decreases.
C) $\Delta$ H_hyd is positive.
D) $\Delta$ H_sol is negative.
E) $\Delta$ H_L is negative.

Question 54

Calculate the number of moles of oxygen that will dissolve in 45 L of water at 20 ^$\omicron$ C if the partial pressure of oxygen is 0.21 atm .Henry's constant for oxygen is 0.0013 mol.L^-1.atm^-1.

A) 0.0062 M
B) 0.0013 M
C) 0.012 M
D) 0.00027 M
E) 0.28

Question 55

For CaCl₂, the absolute value of the enthalpy of hydration is larger than the lattice enthalpy.This means that for CaCl₂

A) the lattice enthalpy is negative.
B) the enthalpy of solution is endothermic.
C) the solubility increases when the temperature increases.
D) the enthalpy of hydration is positive.
E) the enthalpy of solution is exothermic.

Question 56

The condition called the bends results from the rapid release of nitrogen gas in the bloodstream when the diver returns to the surface.Would argon gas or hydrogen gas be suitable replacements for nitrogen gas in "compressed air?" Explain.

Question 57

Calculate the molality of perchloric acid in 9.2 M HClO₄(aq).The density of this solution is 1.54 g/mL.

Question 58

Which of the following is likely to have the smallest exothermic hydration enthalpy?

A) F^
B) I^
C) NO₃^
D) Cl^
E) Br^

Question 59

Calculate the vapor pressure at25 ^$\omicron$ C of a mixture of benzene and toluene in which the mole fraction of benzene is 0.650 .The vapor pressure at 25 ^$\omicron$ C of benzene is 94.6 Torr and that of toluene is 29.1 Torr.

A) 84.4 Torr
B) 124 Torr
C) 51.3 Torr
D) 71.7 Torr
E) 61.5 Torr

Question 60

In a solution of NaClO₄ prepared by dissolving 125 g of sodium perchlorate monohydrate in 500.0 g water, what is the solution molality?

A) 3.56 m
B) 2.04 m
C) 1.78 m
D) 0.90 m
E) 0.250 m

Question 61

the van't Hoff i of HF differs from that of HCl?

Question 62

The osmotic pressure of 1.00 g of a polymer dissolved in benzene to give 200 mL of solution is 1.50 kPa at 25 ^$\omicron$ C .Estimate the average molar mass of the polymer.The gas law constant is 0.0821 L.atm.mol^-1.K^-1.

A) 41 300 g.mol^-1
B) 8260 g.mol^-1
C) 693 g.mol^-1
D) 1650 g.mol^-1
E) 62 000 g.mol^-1

Question 63

Solutions in which intermolecular forces are stronger in the solution than in the pure components have negative enthalpies of mixing.

Question 64

Consider the diagram below.
(a)What is the mixture in the diagram called?
(b)Can the components of this mixture be separated by fractional distillation? Explain.

Question 65

Which of the following pairs have a vant Hoff i factor of 3?

A) Sodium sulfate and potassium chloride
B) Calcium chloride and potassium sulfate
C) Magnesium sulfate and ethylene glycol
D) Glucose and sodium chloride
E) Perchloric acid and barium hydroxide

Question 66

Blood, sweat,And tears are about 0.15 M in sodium chloride.Estimate the osmotic pressure of these solutions at 37 ^$\omicron$ C.The gas constant is 0.0821 L.atm.mol^-1.K^-1.

A) 3.8 atm
B) 11 atm
C) 0.91 atm
D) 1.8 atm
E) 7.6 atm

Question 67

Water and acetone,CH₃COCH₃,both freeze at a higher temperature under pressure.

Question 68

Of the following five materials, which has the lowest freezing point and the highest boiling point?

A) 1.5 m magnesium phosphate
B) 2.0 m potassium chloride
C) 1.0 m sodium chloride
D) 1.5 m aluminum nitrate
E) 1.5 m calcium chloride

Question 69

The critical temperature of N₂ is -147^oC.Nitrogen gas cannot be converted to liquid nitrogen at -73^oC,even at extremely high pressures.

Question 70

The addition of 125 mg of caffeine to 100 g of cyclohexane lowered the freezing point by 0.13 K .Calculate the molar mass of caffeine.The k_f for cyclohexane is 20.1 K.kg.mol^-1.

A) 47.8 g.mol^-1
B) 481 g.mol^-1
C) 96.5 g.mol^-1
D) 19.3 g.mol^-1
E) 193 g.mol^-1

Question 71

The vapor pressures of pure carbon disulfide and carbon tetrachloride are 360 and 99.8 Torr, respectively,At 296 K.What is the vapor pressure of a solution containing 50.0 g of each compound?

A) 260 Torr
B) 274 Torr
C) 241 Torr
D) 33.0 Torr
E) 460 Torr

Question 72

Consider the phase diagram for CO₂ in the text on page 315.A sample of carbon dioxide at 10 ^$\omicron$ C and 10 atm is a liquid.

Question 73

Which of the following pairs have a vant Hoff i factor of 2?

A) Sodium sulfate and potassium chloride
B) Sodium chloride and magnesium sulfate
C) Magnesium sulfate and ethylene glycol
D) Glucose and sodium chloride
E) Perchloric acid and barium hydroxide

Question 74

The freezing point of seawater is about -1.85 ^$\omicron$ C .If seawater is an aqueous solution of sodium chloride,Calculate the molality of seawater.The k_f for water is 1.86 K/m.

A) 1.99 m
B) 0.995 m
C) 3.44 m
D) 3.70 m
E) 0.497 m

Question 75

The vapor pressures of pure carbon disulfide and carbon tetrachloride are 360 and 99.8 Torr, respectively,At 296 K.What is the vapor pressure of a solution containing 50.0 g of each compound?

A) 241 Torr
B) 33.0 Torr
C) 260 Torr
D) 274 Torr
E) 460 Torr

Question 76

Which of the following has the lowest freezing point?

A) 2.0 m sodium perchlorate
B) 1.0 m potassium phosphate
C) 1.5 m aluminum nitrate
D) 1.0 m aluminum sulfate
E) 1.5 m magnesium phosphate

Question 77

Rank the following species in order of increasing vapor pressure at 25 ^$\omicron$ C.
water,diethyl ether,ethanol,mercury

Question 78

The normal boiling point of ethanol is 78 ^$\omicron$ C.If the vapor pressure of ethanol is 13.3 kPa at 34.9 ^$\omicron$ C,calculate the enthalpy of vaporization of ethanol.

Question 79

An animal cell assumes its normal volume when it is placed in a solution with a total solute molarity of 0.3 M .If the cell is placed in a solution with a total solute molarity of 0.1 M,

A) water enters the cell, causing expansion.
B) water leaves the cell, causing contraction.
C) the escaping tendency of water in the cell increases.
D) no movement of water takes place.

Question 80

Which of the following 1.0 M solutions contains the most particles?

A) Ethylene glycol
B) Potassium chloride
C) Magnesium sulfate
D) Glucose
E) Sodium sulfate