Question 1

Select the pair of substances in which the one with the higher vapor pressure at a given temperature is listed first. A)C₇H₁₆,C₅H₁₂ B)CCl₄,CBr₄ C)H₂O,H₂S D)CH₃CH₂OH,CH₃-O-CH₃ E)Xe,Kr

Accepted Answer

In general, for substances with similar molecular weights and intermolecular forces, the substance with the higher vapor pressure at a given temperature is the one with weaker intermolecular forces. C and D contain different functional groups and cannot be directly compared, and E consists of two different elements with different atomic radii and cannot be directly compared. A and B both contain halogens, but the halogen in CCl4 is smaller than the halogen in CBr4, so CCl4 has weaker intermolecular forces and a higher vapor pressure. Therefore, CCl4 should be listed first in the pair.

Question 2

Octane has a vapor pressure of 40.torr at 45.1°C and 400.torr at 104.0°C.What is its heat of vaporization? (R = 8.314 J/K • mol)
A)39.1 kJ/mol
B)46.0 kJ/mol
C)590 kJ/mol
D)710 kJ/mol
E)None of these choices is correct.

Accepted Answer

We can use the Clausius-Clapeyron equation to solve for the heat of vaporization:
ln(P2/P1) = (-ΔHvap/R)(1/T2 - 1/T1)
where P1 and P2 are the vapor pressures at temperatures T1 and T2, respectively, and R is the gas constant.

Plugging in the values given:
ln(400/40) = (-ΔHvap/8.314)(1/377.25 - 1/318.25)
ln(10) = (-ΔHvap/8.314)(0.000694)
ΔHvap = (-8.314 x ln(10) x 1000) / (0.000694)
ΔHvap ≈ -39,100 J/mol

Converting to kilojoules/mol:
ΔHvap ≈ -39.1 kJ/mol

Therefore, the best answer is A) 39.1 kJ/mol.

Question 3

The number of atoms in a face-centered cubic unit cell is
A)1.
B)2.
C)3.
D)4.
E)8.

Accepted Answer

In a face-centered cubic (FCC) unit cell, there are 8 corner atoms, each of which is shared among 8 unit cells, contributing 1/8th of an atom per cell, and 6 face-centered atoms, each shared between 2 cells, contributing 1/2 an atom per cell. This gives a total of (8*(1/8)) + (6*(1/2)) = 1 + 3 = 4 atoms per unit cell.

Question 4

The number of atoms in a body-centered cubic unit cell is
A)1.
B)2.
C)3.
D)4.
E)8.

Accepted Answer

In a body-centered cubic (BCC) unit cell, there is one atom at each of the eight corners and one atom in the center. Each corner atom is shared among eight unit cells, contributing 1/8 of an atom per cell, totaling 1 atom from the corners. The atom in the center is not shared and contributes fully, adding 1 more atom. Therefore, the total number of atoms in a BCC unit cell is 2.

Question 5

At what temperature does ethanol boil on a day in the mountains when the barometric pressure is 547 mmHg? The heat of vaporization of ethanol is 39.3 kJ/mol and its normal boiling point is 78.3°C.(R = 8.314 J/K • mol)
A)76.5°C
B)69.9°C
C)10.0°C
D)77.9°C
E)74.6°C

Accepted Answer

To solve for the boiling point of ethanol, we need to use the Clausius-Clapeyron equation:

ln(P2/P1) = -ΔHvap/R * (1/T2 - 1/T1)

where P1 and T1 are the normal boiling point conditions, P2 is the given pressure, ΔHvap is the heat of vaporization, R is the gas constant, and we are solving for T2.

Plugging in the given values:

ln(547 mmHg/760 mmHg) = - (39.3 kJ/mol) / (8.314 J/K•mol) * (1/T2 - 1/351.45 K)

Simplifying:

-0.285 = -0.00473 * (1/T2 - 0.00284)

-0.285 = -0.00473/T2 + 0.000013

-0.285 - 0.000013 = -0.00473/T2

T2 = -0.285 / -0.00473 + 0.000013 / -0.00473

T2 ≈ 69.9°C

Therefore, the answer is B) 69.9°C.

Question 6

Which corresponds to the temperature-dependent partial pressure above the surface of a liquid?
A)Surface tension
B)Vapor pressure
C)Boiling point
D)Viscosity
E)Capillary action

Accepted Answer

Vapor pressure corresponds to the temperature-dependent partial pressure above the surface of a liquid.

Question 7

Select the pair of substances in which the one with the lower vapor pressure at a given temperature is listed first. A) B)PH₃,NH₃ C)CF₄,CBr₄ D)C₃H₈,C₄H₁₀ E)F₂,Cl₂

Accepted Answer

The answer of Select the pair of substances in which...

Question 8

Liquid sodium can be used as a heat transfer fluid.Its vapor pressure is 40.0 torr at 633°C and 400.0 torr at 823°C.What is its heat of vaporization? A)43.4 kJ/mol B)52.5 kJ/mol C)70.6 kJ/mol D)1.00 × 10² kJ/mol E)3.64 kJ/mol

Accepted Answer

The answer of Liquid sodium can be used as a...

Question 9

Which substance has the highest vapor pressure at room temperature?
A)HF
B)HCl
C)HBr
D)HI
E)All of these substances have the same vapor pressure at room temperature.

Accepted Answer

HCl has the highest vapor pressure at room temperature among the options given. This is because it is the smallest molecule (in terms of molecular weight) compared to HF, HBr, and HI, leading to weaker intermolecular forces and thus a higher vapor pressure.

Question 10

The molar enthalpy of vaporization of boron tribromide is 30.5 kJ/mol,and its normal boiling point is 91°C.What is the vapor pressure of BBr₃ at 20.°C? (R = 8.314 J/K • mol) A)11.5 torr B)659 torr C)255 torr D)66.2 torr E)167 torr

Accepted Answer

To find the vapor pressure of boron tribromide (BBr3) at 20°C, we can use the Clausius-Clapeyron equation, which relates the change in vapor pressure with temperature to the enthalpy of vaporization. The equation in its logarithmic form is:$$ \ln\left(\frac{P_2}{P_1}\right) = -\frac{\Delta H_{vap}}{R} \left(\frac{1}{T_2} - \frac{1}{T_1}\right) $$Given:- $\Delta H_{vap} = 30.5 \, \text{kJ/mol} = 30500 \, \text{J/mol}$ (conversion from kJ to J)- $R = 8.314 \, \text{J/K} \cdot \text{mol}$- $T_1 = 91°C = 364 \, K$ (boiling point, converted from °C to K by adding 273)- $T_2 = 20°C = 293 \, K$ (converted from °C to K by adding 273)- $P_1 = 760 \, \text{torr}$ (normal boiling point pressure)Rearranging the equation to solve for $P_2$, and substituting the given values:$$ \ln\left(\frac{P_2}{760}\right) = -\frac{30500}{8.314} \left(\frac{1}{293} - \frac{1}{364}\right) $$Solving this equation gives the value of $P_2$ in torr, which is approximately 66.2 torr.

Question 11

What is determined by the magnitude of intermolecular forces in a liquid and is a measure of a fluid's resistance to flow?
A)Surface tension
B)Adhesion
C)Polarity
D)Viscosity
E)Cohesion

Accepted Answer

The magnitude of intermolecular forces in a liquid determines the viscosity of the fluid, which is a measure of the fluid's resistance to flow. Surface tension, adhesion, and cohesion are also influenced by intermolecular forces, but they do not directly measure a fluid's resistance to flow. Polarity may play a role in intermolecular forces, but it does not determine viscosity.

Question 12

If a molecule at the surface of a liquid has enough kinetic energy to escape the liquid phase and enter the gas phase,then which of the following terms is used to describe this phenomenon?
A)Boiling point
B)Condensation
C)Vaporization
D)Sublimation
E)Gasification

Accepted Answer

This phenomenon is known as vaporization, which occurs when a molecule has enough kinetic energy to break free from the liquid phase and enter the gas phase. Boiling point refers to the temperature at which a liquid boils and turns into a gas. Condensation occurs when a gas turns into a liquid. Sublimation occurs when a solid turns directly into a gas. Gasification is not a commonly used term in describing phase changes.

Question 13

What is defined as the number of atoms surrounding an atom in a crystal lattice and indicates how tightly the atoms are packed together?
A)the unit cell
B)the radius of the cubic cell
C)the coordination number
D)the area of the cubic cell
E)the atoms themselves

Accepted Answer

The coordination number is defined as the number of atoms surrounding an atom in a crystal lattice and indicates how tightly the atoms are packed together. The unit cell refers to the repeating structure within a crystal lattice, and the radius and area of the cubic cell are measurements of the size of the cell. The atoms themselves are simply the individual particles that make up the crystal lattice.

Question 14

Which of the following factors can contribute to the viscosity for a liquid?
A)Temperature
B)Hydrogen bonding
C)Molecular entanglements
D)London forces
E)All of the answers are correct.

Accepted Answer

All of the listed factors can contribute to the viscosity of a liquid. Temperature affects viscosity by influencing the kinetic energy of the molecules, with higher temperatures leading to lower viscosity. Hydrogen bonding can increase viscosity by creating stronger intermolecular forces, while molecular entanglements can increase viscosity by hindering the flow of molecules. London forces can also contribute to viscosity by creating temporary dipole-dipole attractions between molecules.

Question 15

Which of the following properties indicates the presence of strong intermolecular forces in a liquid?
A)a low heat of vaporization
B)a low critical temperature
C)a low vapor pressure
D)a low boiling point
E)a low melting point

Accepted Answer

A low vapor pressure indicates that the molecules in the liquid are strongly attracted to each other, making it more difficult for them to escape into the gas phase. This is a characteristic of substances with strong intermolecular forces.

Question 16

Which substance has the lowest vapor pressure at room temperature? A)HF B)HCl C)HBr D)HI E)H₂

Accepted Answer

The answer of Which substance has the lowest vapor pressure...

Question 17

If the adhesive forces between a liquid and the walls of a capillary tube are greater than the cohesive forces within the liquid,
A)the liquid level in a capillary tube will rise above the surrounding liquid and the surface in the capillary tube will have a convex meniscus.
B)the liquid level in a capillary tube will rise above the surrounding liquid and the surface in the capillary tube will have a concave meniscus.
C)the liquid level in a capillary tube will drop below the surrounding liquid and the surface in the capillary tube will have a convex meniscus.
D)the liquid level in a capillary tube will drop below the surrounding liquid and the surface in the capillary tube will have a concave meniscus.
E)the liquid level in a capillary tube will be flat.

Accepted Answer

If the adhesive forces between a liquid and the walls of a capillary tube are greater than the cohesive forces within the liquid, then the liquid level in a capillary tube will rise above the surrounding liquid. The shape of the meniscus will depend on the magnitude of the adhesive and cohesive forces. If the adhesive forces are strong enough, they will cause the liquid to climb up the walls of the tube, resulting in a concave meniscus.

Question 18

Palladium crystallizes in a face-centered cubic unit cell.Its density is 12.0 g/cm³ at 27°C.What is the atomic radius of Pd? A)138 pm B)1.95 × 10^-8nm C)1.95 × 10^-8 cm D)154 pm E)0.109 nm

Accepted Answer

The answer of Palladium crystallizes in a face-centered cubic unit...

Question 19

The vapor pressure of ethanol is 400.mmHg at 63.5°C.Its molar heat of vaporization is 39.3kJ/mol.What is the vapor pressure of ethanol,in mmHg,at 34.9°C? (R = 8.314 J/K • mol)
A)109 mmHg
B)220 mmHg
C)366 mmHg
D)376 mmHg
E)1470 mmHg

Accepted Answer

The answer of The vapor pressure of ethanol is 400.mmHg...

Question 20

The molar enthalpy of vaporization of hexane (C₆H₁₄)is 28.9 kJ/mol,and its normal boiling point is 68.73°C.What is the vapor pressure of hexane at 25°C? (R = 8.314 J/K • mol) A)171 torr B)4.44 torr C)117 torr D)3370 torr E)759 torr

Accepted Answer

The Clausius-Clapeyron equation can be used to calculate the vapor pressure at a different temperature given the enthalpy of vaporization and the normal boiling point. The equation is ln(P1/P2) = ΔHvap/R * (1/T2 - 1/T1), where ΔHvap is the molar enthalpy of vaporization, R is the gas constant, T1 and T2 are the initial and final temperatures in Kelvin, and P1 and P2 are the initial and final pressures. Given that the normal boiling point of hexane is 68.73°C (341.88 K) and the enthalpy of vaporization is 28.9 kJ/mol, we can calculate the vapor pressure at 25°C (298.15 K) knowing that the vapor pressure at the boiling point (T1) is 1 atm (760 torr). Rearranging and solving for P2 (the vapor pressure at 25°C) involves converting ΔHvap to J/mol (since R is given in J/K•mol), and using the temperatures in Kelvin. Solving this equation yields a vapor pressure that is closest to the value given in choice A, 171 torr.

Quiz 11: Intermolecular Forces and the Physical Properties of Liquids and Solids

Select the pair of substances in which the one with the higher vapor pressure at a given temperature is listed first.

Octane has a vapor pressure of 40.torr at 45.1°C and 400.torr at 104.0°C.What is its heat of vaporization? (R = 8.314 J/K • mol)

The number of atoms in a face-centered cubic unit cell is

The number of atoms in a body-centered cubic unit cell is

At what temperature does ethanol boil on a day in the mountains when the barometric pressure is 547 mmHg? The heat of vaporization of ethanol is 39.3 kJ/mol and its normal boiling point is 78.3°C.(R = 8.314 J/K • mol)

Which corresponds to the temperature-dependent partial pressure above the surface of a liquid?

Select the pair of substances in which the one with the lower vapor pressure at a given temperature is listed first.

Liquid sodium can be used as a heat transfer fluid.Its vapor pressure is 40.0 torr at 633°C and 400.0 torr at 823°C.What is its heat of vaporization?

Which substance has the highest vapor pressure at room temperature?

The molar enthalpy of vaporization of boron tribromide is 30.5 kJ/mol,and its normal boiling point is 91°C.What is the vapor pressure of BBr₃ at 20.°C? (R = 8.314 J/K • mol)

What is determined by the magnitude of intermolecular forces in a liquid and is a measure of a fluid's resistance to flow?

If a molecule at the surface of a liquid has enough kinetic energy to escape the liquid phase and enter the gas phase,then which of the following terms is used to describe this phenomenon?

What is defined as the number of atoms surrounding an atom in a crystal lattice and indicates how tightly the atoms are packed together?

Which of the following factors can contribute to the viscosity for a liquid?

Which of the following properties indicates the presence of strong intermolecular forces in a liquid?

Which substance has the lowest vapor pressure at room temperature?

If the adhesive forces between a liquid and the walls of a capillary tube are greater than the cohesive forces within the liquid,

Palladium crystallizes in a face-centered cubic unit cell.Its density is 12.0 g/cm³ at 27°C.What is the atomic radius of Pd?

The vapor pressure of ethanol is 400.mmHg at 63.5°C.Its molar heat of vaporization is 39.3kJ/mol.What is the vapor pressure of ethanol,in mmHg,at 34.9°C? (R = 8.314 J/K • mol)

The molar enthalpy of vaporization of hexane (C₆H₁₄) is 28.9 kJ/mol,and its normal boiling point is 68.73°C.What is the vapor pressure of hexane at 25°C? (R = 8.314 J/K • mol)