Question 1

Which of the following compounds has the highest boiling point?

Accepted Answer

Water has the highest boiling point because it has the strongest intermolecular forces (hydrogen bonding).

Question 2

Molecules of a liquid can pass into the vapor phase only if the

Accepted Answer

Molecules can transition from the liquid phase to the vapor phase when they possess enough kinetic energy to overcome the intermolecular forces that hold them together in the liquid state. This process is not solely dependent on factors like surface tension, the temperature being near the boiling point, or the vapor pressure being high, although these can influence the rate of evaporation.

Question 3

The magnitude of the heats of vaporization,fusion and sublimation of a substance reflect the

Accepted Answer

The heats of vaporization, fusion, and sublimation are all related to the strength of intermolecular forces between molecules. Stronger forces require more energy to break, resulting in higher enthalpy changes during state changes. Density, boiling point, melting point, and covalent bonding strength are not necessarily related to intermolecular forces and cannot fully explain the magnitudes of these heats.

Question 4

Bromine is one of only two elements that is a liquid at room temperature.Bromine has a heat of vaporization of 30.91 kJ/mol and its boiling point is 59°C.What is the entropy of vaporization for bromine?

Accepted Answer

The entropy of vaporization ($\Delta S_{vap}$) can be calculated using the formula $\Delta S_{vap} = \frac{\Delta H_{vap}}{T_{b}}$, where $\Delta H_{vap}$ is the heat of vaporization and $T_{b}$ is the boiling point in Kelvin. First, convert the boiling point from Celsius to Kelvin: $59°C + 273.15 = 332.15 K$. Then, plug the values into the formula: $\Delta S_{vap} = \frac{30.91 \times 10^3 J/mol}{332.15 K} = 93.1 J/(mol \cdot K)$.

Question 5

As a liquid evaporates at a temperature below its boiling point,the temperature of the liquid

Accepted Answer

As a liquid evaporates, the most energetic molecules escape the surface, decreasing the average kinetic energy (temperature) of the remaining molecules. Therefore, the temperature of the liquid decreases.

Question 6

For the process: HNO₃(g)⇌ HNO₃(l) ΔH° is -39.04 kJ/mol and ΔS° is -111.74 J/(mol ∙ K).What is the normal boiling point of pure HNO₃?

Accepted Answer

The normal boiling point of a substance is the temperature at which its vapor pressure equals atmospheric pressure. At this point, the Gibbs free energy change (ΔG°) for the phase transition is zero. The relationship between ΔG°, ΔH°, and ΔS° is given by the equation ΔG° = ΔH° - TΔS°. Setting ΔG° to zero for the boiling point and solving for T (temperature in Kelvin) gives T = ΔH° / ΔS°. Given ΔH° = -39.04 kJ/mol = -39040 J/mol and ΔS° = -111.74 J/(mol·K), the temperature T in Kelvin is T = -39040 J/mol / -111.74 J/(mol·K) = 349.4 K. Converting this to Celsius gives 349.4 K - 273.15 = 76.2°C.

Question 7

Ethyl chloride,C₂H₅Cl,is used as a local anesthetic.It works by cooling tissue as it vaporizes.The heat of vaporization is 26.4 kJ/mol.How much heat could be removed by 10.0 g of ethyl chloride?

Accepted Answer

The molar mass of ethyl chloride (C2H5Cl) is approximately 64.5 g/mol. For 10.0 g, the number of moles is 10.0 g / 64.5 g/mol = 0.155 moles. The heat removed is 0.155 moles * 26.4 kJ/mol = 4.09 kJ.

Question 8

When a substance melts at its normal melting point,the sign of ΔH is ________ and the sign of ΔS of this phase change is ________.

Accepted Answer

The answer of When a substance melts at its normal...

Question 9

The normal boiling point occurs when the

Accepted Answer

The normal boiling point of a substance occurs when the vapor pressure of the liquid equals the external pressure, which is typically one atmosphere. This is because at the normal boiling point, the energy added to the liquid is sufficient to break the intermolecular forces within the liquid and form a vapor, which then exerts a pressure equal to the external pressure. Therefore, the correct answer is C.

Question 10

Which of the following substances has the highest boiling point?

Accepted Answer

The molecule in choice A has the highest boiling point due to its longer carbon chain and the presence of multiple sulfur atoms, which increases the strength of intermolecular forces. Choice C also has sulfur atoms, but not as many as choice A, and choice D has a smaller molecule size. Xe is a noble gas and does not have intermolecular forces in the same way as molecules with covalent bonds, so it has a very low boiling point.

Question 11

When a liquid is heated at its boiling point,the

Accepted Answer

At the boiling point, the temperature of the liquid remains constant as the energy is used for the phase change from liquid to vapor, not for increasing the temperature.

Question 12

Which of the following phase changes has a positive value for its entropy change?

Accepted Answer

When water boils, it undergoes a phase change from a liquid to a gas, which increases the disorder or randomness of the particles in the system, leading to an increase in entropy.

Question 13

For a particular compound,which is expected to be the largest in general?

Accepted Answer

The molar heat of vaporization is generally higher than the molar heat of fusion and the heat required to raise the temperature of one mole of a substance by 10.0°C. This is because vaporization involves breaking stronger intermolecular forces between molecules, while fusion and temperature increase only involve weaker intermolecular forces. Therefore, D is expected to be the largest in general.

Question 14

How much heat is released when 75.0 g of steam at 100.0°C is cooled to ice at -15.0°C? The enthalpy of vaporization of water is 40.67 kJ/mol,the enthalpy of fusion for water is 6.01 kJ/mol,the molar heat capacity of liquid water is 75.4 J/(mol ∙ °C),and the molar heat capacity of ice is 36.4 J/(mol ∙ °C).

Accepted Answer

To find the total heat released, calculate the heat for each phase change and temperature change: 1) Condense steam to water at 100°C, 2) Cool water from 100°C to 0°C, 3) Freeze water to ice at 0°C, 4) Cool ice from 0°C to -15°C. Sum these values to get the total heat released.

Question 15

The property of a liquid that measure the liquid's resistance to flow is

Accepted Answer

Viscosity is the property of a liquid that measures its resistance to flow. A liquid with high viscosity will be thick and flow slow, whereas a liquid with low viscosity will be thin and flow quickly. Boiling point and heat of vaporization relate to the liquid's ability to change from a liquid to a gas, whereas surface tension measures the cohesive force of the liquid's surface.

Question 16

Which is expected to have the highest surface tension at 25°?

Accepted Answer

Glycerol (C₃H₅(OH)₃) has the highest surface tension due to its ability to form extensive hydrogen bonding networks, which increases intermolecular forces compared to the other options.

Question 17

Which of the following is most likely to have the highest viscosity at 25°C?

Accepted Answer

Ethylene glycol (HOCH₂CH₂OH) has strong hydrogen bonding due to its two hydroxyl groups, leading to higher viscosity compared to the other compounds listed.

Question 18

For which of the following phase changes is the sign of ΔS negative?

Accepted Answer

The formation of snow from water vapor involves a transition from a gas to a solid, which decreases the disorder of the system, resulting in a negative change in entropy (ΔS).

Question 19

CFC-11 (trichlorofluoromethane,CCl₃F)has been used for many years as the working fluid in refrigerators.Given its heat of vaporization is 26.88 kJ/mol and its entropy of vaporization is 90.51 J/(mol ∙ K),what is the boiling point of CFC-11?

Accepted Answer

The boiling point of CFC-11 can be calculated using the Clausius-Clapeyron equation, which relates the heat of vaporization ($\Delta H_{vap}$) and the entropy of vaporization ($\Delta S_{vap}$) to the boiling point ($T_b$) at 1 atm pressure. The equation in a simplified form for boiling point calculation is $T_b = \frac{\Delta H_{vap}}{\Delta S_{vap}}$. Given $\Delta H_{vap} = 26.88 \, \text{kJ/mol} = 26880 \, \text{J/mol}$ and $\Delta S_{vap} = 90.51 \, \text{J/(mol} \cdot \text{K)}$, the boiling point $T_b$ is calculated as $T_b = \frac{26880 \, \text{J/mol}}{90.51 \, \text{J/(mol} \cdot \text{K)}} = 297 \, \text{K}$. To convert to degrees Celsius, subtract 273.15 from the Kelvin temperature, resulting in $23.85^\circ C$, which rounds to $23.8^\circ C$.

Question 20

The vapor pressure of a pure liquid increases as the

Accepted Answer

Vapor pressure is directly proportional to temperature, so as the temperature of the liquid phase increases, the vapor pressure will also increase.

Quiz 10: Liquids,solids,and Phase Changes

Which of the following compounds has the highest boiling point?

Molecules of a liquid can pass into the vapor phase only if the

The magnitude of the heats of vaporization,fusion and sublimation of a substance reflect the

Bromine is one of only two elements that is a liquid at room temperature.Bromine has a heat of vaporization of 30.91 kJ/mol and its boiling point is 59°C.What is the entropy of vaporization for bromine?

As a liquid evaporates at a temperature below its boiling point,the temperature of the liquid

For the process: HNO₃(g) ⇌ HNO₃(l) ΔH° is -39.04 kJ/mol and ΔS° is -111.74 J/(mol ∙ K) .What is the normal boiling point of pure HNO₃?

Ethyl chloride,C₂H₅Cl,is used as a local anesthetic.It works by cooling tissue as it vaporizes.The heat of vaporization is 26.4 kJ/mol.How much heat could be removed by 10.0 g of ethyl chloride?

When a substance melts at its normal melting point,the sign of ΔH is and the sign of ΔS of this phase change is .

The normal boiling point occurs when the

Which of the following substances has the highest boiling point?

When a liquid is heated at its boiling point,the

Which of the following phase changes has a positive value for its entropy change?

For a particular compound,which is expected to be the largest in general?

The property of a liquid that measure the liquid's resistance to flow is

Which is expected to have the highest surface tension at 25°?

Which of the following is most likely to have the highest viscosity at 25°C?

For which of the following phase changes is the sign of ΔS negative?

CFC-11 (trichlorofluoromethane,CCl₃F) has been used for many years as the working fluid in refrigerators.Given its heat of vaporization is 26.88 kJ/mol and its entropy of vaporization is 90.51 J/(mol ∙ K) ,what is the boiling point of CFC-11?

The vapor pressure of a pure liquid increases as the

Quiz 10: Liquids,solids,and Phase Changes

Which of the following compounds has the highest boiling point?

Molecules of a liquid can pass into the vapor phase only if the

The magnitude of the heats of vaporization,fusion and sublimation of a substance reflect the

Bromine is one of only two elements that is a liquid at room temperature.Bromine has a heat of vaporization of 30.91 kJ/mol and its boiling point is 59°C.What is the entropy of vaporization for bromine?

As a liquid evaporates at a temperature below its boiling point,the temperature of the liquid

For the process: HNO3(g) ⇌ HNO3(l) ΔH° is -39.04 kJ/mol and ΔS° is -111.74 J/(mol ∙ K) .What is the normal boiling point of pure HNO3?

Ethyl chloride,C2H5Cl,is used as a local anesthetic.It works by cooling tissue as it vaporizes.The heat of vaporization is 26.4 kJ/mol.How much heat could be removed by 10.0 g of ethyl chloride?

When a substance melts at its normal melting point,the sign of ΔH is ________ and the sign of ΔS of this phase change is ________.

The normal boiling point occurs when the

Which of the following substances has the highest boiling point?

When a liquid is heated at its boiling point,the

Which of the following phase changes has a positive value for its entropy change?

For a particular compound,which is expected to be the largest in general?

The property of a liquid that measure the liquid's resistance to flow is

Which is expected to have the highest surface tension at 25°?

Which of the following is most likely to have the highest viscosity at 25°C?

For which of the following phase changes is the sign of ΔS negative?

CFC-11 (trichlorofluoromethane,CCl3F) has been used for many years as the working fluid in refrigerators.Given its heat of vaporization is 26.88 kJ/mol and its entropy of vaporization is 90.51 J/(mol ∙ K) ,what is the boiling point of CFC-11?

The vapor pressure of a pure liquid increases as the

For the process: HNO₃(g) ⇌ HNO₃(l) ΔH° is -39.04 kJ/mol and ΔS° is -111.74 J/(mol ∙ K) .What is the normal boiling point of pure HNO₃?

Ethyl chloride,C₂H₅Cl,is used as a local anesthetic.It works by cooling tissue as it vaporizes.The heat of vaporization is 26.4 kJ/mol.How much heat could be removed by 10.0 g of ethyl chloride?

When a substance melts at its normal melting point,the sign of ΔH is and the sign of ΔS of this phase change is .

CFC-11 (trichlorofluoromethane,CCl₃F) has been used for many years as the working fluid in refrigerators.Given its heat of vaporization is 26.88 kJ/mol and its entropy of vaporization is 90.51 J/(mol ∙ K) ,what is the boiling point of CFC-11?