Chemistry II Chapter 12 Intermolecular Forces
This quiz is to test your knowledge about Chapter 12. Chapter 12 covers information about states of matter, phase changes, and intermolecular forces.
- 1.
Which one of the following decreases as the strength of the attractive intermolecular forces increases?
- A.
The heat of vaporization
- B.
The normal boiling temperature
- C.
The extent of deviations from the ideal gas law
- D.
The sublimation temperature of a solid
- E.
The vapor pressure of a liquid
Correct Answer
E. The vapor pressure of a liquidExplanation
As the strength of the attractive intermolecular forces increases, the molecules in a liquid are held more tightly together. This makes it more difficult for the molecules to escape from the liquid phase and enter the gas phase, resulting in a decrease in the vapor pressure of the liquid.Rate this question:
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- 2.
Order the intermoleuclar forces from weakest to strongest.
- A.
Dipole-dipole, london dispersion, ionic, hydrogen bonding
- B.
London dispersion, dipole-dipole, hydrogen bonding, ionic
- C.
Hydrogen bonding, dipole-dipole, london dispersion, ionic
- D.
Dipole-dipole, ionic, london dispersion, hydrogen bonding
- E.
London dispersion, ionic, dipole-dipole, hydrogen bonding
Correct Answer
B. London dispersion, dipole-dipole, hydrogen bonding, ionicExplanation
The intermolecular forces are ordered from weakest to strongest as follows: london dispersion, dipole-dipole, hydrogen bonding, ionic. London dispersion forces are the weakest intermolecular forces and occur between all molecules. Dipole-dipole forces are stronger and occur between polar molecules. Hydrogen bonding is even stronger and occurs between molecules that have a hydrogen atom bonded to a highly electronegative atom like nitrogen, oxygen, or fluorine. Ionic forces are the strongest intermolecular forces and occur between ions with opposite charges.Rate this question:
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- 3.
Which of the following would you expect to have the highest boiling point?
- A.
Fluorine
- B.
Chlorine
- C.
Bromine
- D.
Iodine
- E.
All would have the same boiling point
Correct Answer
D. IodineExplanation
Iodine has the highest molar massRate this question:
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- 4.
On a relative basis, the weaker the intermoleuclar forces in a substance,
- A.
The greater its heat of vaporization
- B.
The more it deviates from ideal gas behavior
- C.
The greater its vapor pressure at a particular temperature
- D.
The higher its melting point
- E.
None of these
Correct Answer
C. The greater its vapor pressure at a particular temperatureExplanation
The greater the intermolecular forces in a substance, the stronger the attractions between its particles. These attractions make it more difficult for the substance to change from a liquid to a gas, resulting in a lower vapor pressure. Therefore, if the intermolecular forces are weaker, there will be less attraction between the particles, allowing the substance to easily transition from a liquid to a gas and have a higher vapor pressure at a particular temperature.Rate this question:
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- 5.
Water sits in an open beaker. Assuming contant temperature and pressure, the rate of evaporation decreases as the water evaporates.
- A.
True
- B.
False
Correct Answer
B. FalseExplanation
The statement is false because the rate of evaporation actually increases as water evaporates. As the water level decreases in the beaker, the surface area of the remaining water increases, allowing for more molecules to escape and evaporate. Therefore, the rate of evaporation will continue to increase until all the water has evaporated.Rate this question:
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- 6.
At normal atmospheric pressure and a temperature of 0oC, which phase(s) of H2O can exist?
- A.
Ice and water
- B.
Ice and water vapor
- C.
Water only
- D.
Water vapor only
- E.
Ice only
Correct Answer
A. Ice and waterExplanation
At normal atmospheric pressure and a temperature of 0oC, both ice and water can exist. This is because at this temperature, water freezes and turns into ice, while some water remains in its liquid form. Therefore, both phases of H2O, ice and water, can coexist at this specific temperature and pressure.Rate this question:
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- 7.
Assume 12,500 J of energy is added to 2.0 moles of water as an ice sample at 0oC. The heat of fusion is 6.02 kJ/mol. the specific heat of liquid water is 4.18 J/mol K. the heat of vaporization is 40.6 kJ/mol. The resulting sample contains which of the following?
- A.
Only ice
- B.
Ice and water
- C.
Only water
- D.
Water and water vapor
- E.
Only water vapor
Correct Answer
C. Only waterExplanation
When energy is added to the ice sample, it first undergoes a phase change from solid to liquid, which requires the heat of fusion. The heat of fusion is given as 6.02 kJ/mol, and since there are 2.0 moles of water, the energy required for this phase change is 2.0 * 6.02 kJ = 12.04 kJ.
After the phase change, the remaining energy (12,500 J - 12.04 kJ = 11,488 J) is used to increase the temperature of the liquid water. The specific heat of liquid water is given as 4.18 J/mol K, so the temperature increase can be calculated using the formula Q = m * c * ΔT, where Q is the energy, m is the mass, c is the specific heat, and ΔT is the change in temperature. Rearranging the formula, we can calculate ΔT as ΔT = Q / (m * c) = 11,488 J / (2.0 mol * 4.18 J/mol K) = 1377 K.
Since the initial temperature was 0°C, the final temperature would be 0°C + 1377 K = 1377°C. At this temperature, the water would be in the form of water vapor. Therefore, the resulting sample contains only water.Rate this question:
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- 8.
Which of the following processes must exist in equilibrium with the evaporation process when a measurement of vapor pressure is made?
- A.
Fusion
- B.
Vaporization
- C.
Sublimation
- D.
Boiling
- E.
Condensation
Correct Answer
E. CondensationExplanation
When a measurement of vapor pressure is made, the process of condensation must exist in equilibrium with the evaporation process. This is because vapor pressure is the pressure exerted by the vapor molecules in equilibrium with the liquid or solid phase. Evaporation occurs when molecules escape from the liquid or solid phase into the gas phase, while condensation is the process of gas molecules returning to the liquid or solid phase. In order to measure vapor pressure accurately, both evaporation and condensation must occur at the same rate, establishing equilibrium.Rate this question:
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- 9.
What is responsible for capillary action, a property of liquids?
- A.
Surface tension
- B.
Cohesive forces
- C.
Adhesive forces
- D.
Viscosity
- E.
Two of these
Correct Answer
E. Two of theseExplanation
Capillary action, the ability of liquids to flow against gravity in narrow spaces, is caused by a combination of two factors: surface tension and cohesive forces. Surface tension is the force that holds the molecules of a liquid together at the surface, creating a "skin" that allows the liquid to retain its shape. Cohesive forces are the attractive forces between molecules of the same substance, which help hold the liquid together. Both of these factors work together to enable capillary action. Adhesive forces, which are the attractive forces between molecules of different substances, and viscosity, the resistance of a liquid to flow, are not solely responsible for capillary action but may play a role in certain cases.Rate this question:
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- 10.
When a nonpolar liquid displays a convex meniscus, which of the following explains this behavior?
- A.
It has a low surface tension, and therefore clings to the glass
- B.
The cohesive forces are stronger than the adhesive forces toward the glass
- C.
The adhesive forces toward the glass are stronger than the cohesive forces
- D.
The liquid's viscosity is low
- E.
None of these
Correct Answer
B. The cohesive forces are stronger than the adhesive forces toward the glassExplanation
When a nonpolar liquid displays a convex meniscus, it suggests that the cohesive forces within the liquid are stronger than the adhesive forces between the liquid and the glass surface. This means that the molecules of the liquid are more attracted to each other than they are to the glass, causing the liquid to pull away from the glass and form a curved surface. This behavior is typically observed in nonpolar liquids with low surface tension, as they tend to minimize contact with polar surfaces like glass.Rate this question:
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- 11.
A liquid placed in a closed container will evaporate until equilibrium is reached. At equilibrium, which of the statements bleow is NOT true?
- A.
The partial pressure exerted by the vapor molecules is called teh vapor pressure of the liquid
- B.
Liquid molecules are still evaporating
- C.
The number of vapor molecules remains essentially constant
- D.
The boundary between the liquid and vapor disappears
- E.
All of these are true
Correct Answer
D. The boundary between the liquid and vapor disappearsExplanation
At equilibrium, the boundary between the liquid and vapor does not disappear. Instead, it remains intact, with the liquid and vapor coexisting in a dynamic equilibrium. This means that while the liquid molecules are still evaporating, an equal number of vapor molecules are condensing back into the liquid phase. The vapor pressure of the liquid refers to the partial pressure exerted by the vapor molecules, and the number of vapor molecules remains essentially constant at equilibrium. Therefore, the statement "the boundary between the liquid and vapor disappears" is not true.Rate this question:
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- 12.
A cetain substance, X, has a triple-point temperature of 20oC at a pressure of 2.0 atm.Which one of the statements can NOT be true?
- A.
X can exist as a liquid above 20oC
- B.
X can exist as a solid above 20oC
- C.
Liquid X can exist as a stable phase at 25oC and 1 atm
- D.
Both liquid and solid X have the same vapor pressure at 20oC
- E.
All of these could be true
Correct Answer
C. Liquid X can exist as a stable pHase at 25oC and 1 atmExplanation
If liquid X can exist as a stable phase at 25oC and 1 atm, it means that the substance X can exist in a liquid state at a temperature higher than its triple-point temperature. However, according to the definition of a triple point, it is the temperature and pressure at which all three phases of a substance (solid, liquid, and gas) can coexist in equilibrium. Therefore, if X can exist as a stable liquid at 25oC, it contradicts the concept of a triple point and cannot be true.Rate this question:
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- 13.
The vapor pressure of water is 1.0 atm at 373 K, and the enthalpy of vaporization is 40.7 kJ mol-1. Estimate the vapor pressure at temperature 363
- A.
1.5 atm
- B.
0.697 atm
- C.
760 torr
- D.
490 torr
- E.
12.2 atm
Correct Answer
B. 0.697 atmExplanation
The vapor pressure of a substance is directly proportional to its temperature. In this case, the given vapor pressure is 1.0 atm at 373 K. To estimate the vapor pressure at a lower temperature of 363 K, we can use the Clausius-Clapeyron equation: ln(P2/P1) = -(ΔHvap/R)(1/T2 - 1/T1), where P1 and T1 are the initial pressure and temperature, and P2 and T2 are the final pressure and temperature. Plugging in the values, we get ln(P2/1.0) = -(40.7 kJ mol-1/8.314 J mol-1 K-1)(1/363 K - 1/373 K). Solving for P2, we find that the vapor pressure at 363 K is approximately 0.697 atm.Rate this question:
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