Q: Liquid sodium is used as a heat transfer fluid. Its vapor pressure is 40.0 torr at 633°C and 400.0 torr at 823°C. Using the Clausius-Clapeyron equation, what is the heat of vaporization ($\Delta H_{\text{vap}}$) in kJ/mole? (Assume ideal behavior and $R = 8.314$ J/mol·K.)

$\Delta H_{\text{vap}} = 83.1$ kJ/mole

Q: A liquid's vapor pressure doubles when the temperature is raised from 85.0°C to 95.0°C. Estimate the molar heat of vaporization ($\Delta H_{\text{vap}}$) in kJ/mole. ($R = 8.314$ J/mol·K)

$\Delta H_{\text{vap}} = 48.2$ kJ/mole

Q: Which of the following is a correct application of the Clausius-Clapeyron equation for determining the enthalpy of vaporization?

$\ln \left( \frac{P_2}{P_1} \right) = -\frac{\Delta H_{\text{vap}}}{R} \left( \frac{1}{T_2} - \frac{1}{T_1} \right)$

Question 1

Liquid sodium is used as a heat transfer fluid. Its vapor pressure is 40.0 torr at 633°C and 400.0 torr at 823°C. Using the Clausius-Clapeyron equation, what is the heat of vaporization ($\Delta H_{	ext{vap}}$) in kJ/mole? (Assume ideal behavior and $R = 8.314$ J/mol·K.)

Accepted Answer

$\Delta H_{	ext{vap}} = 83.1$ kJ/mole

Question 2

A pressure cooker operates at a total pressure of 2.00 atm. Given that the normal boiling point of water is 100.0°C and $\Delta H_{	ext{vap}}$ for water is 40.65 kJ/mole, what is the highest cooking temperature (in K) achievable in the cooker? ($R = 8.314$ J/mol·K)

Accepted Answer

$T = 393$ K

Question 3

The vapor pressure of a liquid is 83.6 mmHg at 42.5°C. If the molar heat of vaporization ($\Delta H_{	ext{vap}}$) is 63.5 kJ/mole, what is the vapor pressure (in mmHg) at 74.2°C? ($R = 8.314$ J/mol·K)

Accepted Answer

1.1 	imes 10^2$ mmHg

Question 4

A liquid's vapor pressure doubles when the temperature is raised from 85.0°C to 95.0°C. Estimate the molar heat of vaporization ($\Delta H_{	ext{vap}}$) in kJ/mole. ($R = 8.314$ J/mol·K)

Accepted Answer

$\Delta H_{	ext{vap}} = 48.2$ kJ/mole

Question 5

Vanadium (molar mass = 50.94 g/mole) crystallizes in a body-centered cubic (bcc) lattice with a unit cell edge length of 305 pm. What is the density (in g/cm$^3$) of vanadium? (1 cm = $10^{10}$ pm)

Accepted Answer

6.11 g/cm$^3$

Question 6

Copper (molar mass = 63.55 g/mole) crystallizes in a face-centered cubic (fcc) lattice. If the density of copper is 8.96 g/cm$^3$, what is the length (in pm) of the unit cell edge? (1 cm = $10^{10}$ pm)

Accepted Answer

361 pm

Question 7

A face-centered cubic (fcc) cell contains 8 'X' atoms at the corners and 6 'Y' atoms at the faces. What is the empirical formula of the solid?

Accepted Answer

XY$_3$

Question 8

Nickel(II) oxide, NiO (molar mass = 74.69 g/mole), crystallizes in a face-centered cubic lattice. Given the density of NiO is 6.67 g/cm$^3$, calculate the radius (in pm) of its unit cell. ($a = 8r$, 1 cm = $10^{10}$ pm)

Accepted Answer

104 pm

Question 9

Which of the following best describes the relationship between vapor pressure and temperature for a pure liquid, according to the Clausius-Clapeyron equation?

Accepted Answer

Vapor pressure increases exponentially with temperature.

Question 10

A chemist wants to design a new pressure cooker for use at high altitudes, where atmospheric pressure is lower. If the enthalpy of vaporization of water remains constant, what must be done to the pressure inside the cooker to maintain a boiling point of 100°C?

Accepted Answer

Increase the pressure inside the cooker above atmospheric pressure.

Question 11

If the vapor pressure of a liquid at 25°C is 100 mmHg and its heat of vaporization is 40 kJ/mol, what will be the vapor pressure at 35°C? ($R = 8.314$ J/mol·K)

Accepted Answer

Approximately 180 mmHg

Question 12

Which of the following statements about the structure of a body-centered cubic (bcc) lattice is correct?

Accepted Answer

There are 2 atoms per unit cell in a bcc lattice.

Question 13

A solid has a face-centered cubic (fcc) lattice. If the edge length of the unit cell is doubled, what happens to the density of the solid (assuming the mass per unit cell remains constant)?

Accepted Answer

The density decreases by a factor of 8.

Question 14

Which of the following is a correct application of the Clausius-Clapeyron equation for determining the enthalpy of vaporization?

Accepted Answer

$\ln \left( \frac{P_2}{P_1} ight) = -\frac{\Delta H_{	ext{vap}}}{R} \left( \frac{1}{T_2} - \frac{1}{T_1} ight)$

Question 15

A certain liquid has a normal boiling point of 78.0°C and a heat of vaporization of 38.7 kJ/mol. What is its vapor pressure at 60.0°C? ($R = 8.314$ J/mol·K, 1 atm = 760 mmHg)

Accepted Answer

268 mmHg

Question 16

Which of the following best explains why the vapor pressure of a liquid increases with temperature?

Accepted Answer

As temperature increases, more molecules have enough kinetic energy to escape the liquid phase.

Question 17

A solid has a unit cell edge length of 400 pm and contains 4 atoms per unit cell. If the molar mass is 100 g/mol and Avogadro's number is $6.022 	imes 10^{23}$ mol$^{-1}$, what is the density of the solid in g/cm$^3$? (1 cm = $10^{10}$ pm)

Accepted Answer

4.16 g/cm$^3$

Question 18

Which of the following is true for the number of atoms in a face-centered cubic (fcc) unit cell?

Accepted Answer

There are 4 atoms per unit cell.

Question 19

A chemist observes that a certain liquid boils at a lower temperature on a mountain than at sea level. Which principle best explains this observation?

Accepted Answer

The atmospheric pressure is lower at higher altitudes, so the vapor pressure required for boiling is reached at a lower temperature.

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