Q: A 2.00 L container holds a mixture of oxygen ($$O_2) $$and nitrogen ($$N_2) $$gases at a total pressure of 1.50 atm. If the mole fraction of $$O_2 is 0.40$$, what is the partial pressure of $$O_2$$?

$$P_{O_2$} = X_{O_2$} \times P_{\text{total}} = 0.40 \times 1.50 = 0.60\ \text{atm}$$

Question 1

Ice cores are used to study Earth's atmospheric conditions from hundreds of thousands of years ago. Which of the following best explains how scientists use ice cores to determine past atmospheric temperatures?

Accepted Answer

By measuring the ratio of oxygen isotopes in the trapped gas bubbles, which reflects the temperature at the time the ice formed.

Question 2

According to the kinetic molecular theory, which of the following statements is NOT a postulate of the theory?

Accepted Answer

Gas particles exert attractive and repulsive forces on each other.

Question 3

A sample of nitrogen gas ($$N_2) $$and a sample of helium gas ($$He) $$are both at the same temperature. Which statement best describes the distribution of molecular speeds in the two samples?

Accepted Answer

Helium atoms have a broader distribution of speeds and a higher average speed than nitrogen molecules.

Question 4

Which of the following correctly expresses the relationship between pressure, force, and area?

Accepted Answer

$$P = \frac{F}{A}$$

Question 5

A weather balloon contains 5.00 L of helium gas at 1.00 atm and 300 K. If the balloon rises to a region where the pressure is 0.500 atm and the temperature is 250 K, what will be the new volume of the balloon? (Assume ideal gas behavior.)

Accepted Answer

$$V_2$$ = \frac{$$P_1$$ $$V_1$$ $$T_2$$}{$$T_1$$ $$P_2$$} = \frac{1.00 	imes 5.00 	imes 250}{300 	imes 0.500} = 8.33\ 	ext{L}$$

Question 6

Which of the following best explains why hurricanes strengthen over warm ocean waters in terms of gas laws and molecular properties?

Accepted Answer

Warm water increases the density of water vapor in the air, providing more latent heat energy as the vapor condenses.

Question 7

A 2.00 L container holds a mixture of oxygen ($$O_2) $$and nitrogen ($$N_2) $$gases at a total pressure of 1.50 atm. If the mole fraction of $$O_2 is 0.40$$, what is the partial pressure of $$O_2$$?

Accepted Answer

$$P_{O_2$} = X_{O_2$} 	imes P_{	ext{total}} = 0.40 	imes 1.50 = 0.60\ 	ext{atm}$$

Question 8

Which of the following molecules can form hydrogen bonds with water?

Accepted Answer

Ammonia ($$NH_3)$$

Question 9

Rank the following intermolecular forces in order of increasing strength for small molecules: (1) dispersion, (2) dipole-dipole, (3) hydrogen bonding.

Accepted Answer

dispersion \u003c dipole-dipole \u003c hydrogen bonding

Question 10

Which of the following best describes how vapor pressure is related to the strength of intermolecular forces?

Accepted Answer

A liquid with strong intermolecular forces has a low vapor pressure.

Question 11

Which of the following is a real-life application that depends on the high enthalpy of vaporization ($$\Delta H_{	ext{vap}}) of $$water?

Accepted Answer

Sweating as a cooling mechanism in humans.

Question 12

Which of the following best explains why all molecules experience dispersion forces?

Accepted Answer

Because all molecules have electrons that can form temporary dipoles.

Question 13

A 0.500 g sample of an unknown gas occupies 300 mL at 1.00 atm and 273 K. What is the molar mass of the gas? (Use $$R = 0.0821\ 	ext{L} \cdot 	ext{atm} \cdot 	ext{mol}^{-1} \cdot 	ext{K}^{-1})$$

Accepted Answer

$$M = \frac{mRT}{PV} = \frac{0.500 	imes 0.0821 	imes 273}{1.00 	imes 0.300} = 37.3\ 	ext{g/mol}$$

Question 14

Which of the following best describes a foam in chemical terms?

Accepted Answer

A colloidal dispersion of a gas in a liquid.

Question 15

Which of the following molecules would you expect to have the highest boiling point, and why?

Accepted Answer

Water ($$H_2O$$), because it can form hydrogen bonds.

Question 16

A mixture of gases contains 2.0 mol $$N_2$$, 1.0 mol $$O_2$$, and 1.0 mol $$CO_2 at a $$total pressure of 2.0 atm. What is the partial pressure of $$O_2$$?

Accepted Answer

$$P_{O_2$} = \frac{1.0}{4.0} 	imes 2.0 = 0.50\ 	ext{atm}$$

Question 17

Which of the following best explains the role of hydrogen bonding in living systems?

Accepted Answer

Hydrogen bonding stabilizes the structure of proteins and DNA.

Question 18

Which of the following statements about the Boltzmann distribution of molecular speeds is correct?

Accepted Answer

At higher temperatures, the distribution of molecular speeds becomes broader and the average speed increases.

Question 19

A 1.00 L flask contains 0.500 mol of $$CO_2$$ gas at 300 K. What is the pressure in the flask? (Use $$R = 0.0821\ 	ext{L} \cdot 	ext{atm} \cdot 	ext{mol}^{-1} \cdot 	ext{K}^{-1})$$

Accepted Answer

$$P = \frac{nRT}{V} = \frac{0.500 	imes 0.0821 	imes 300}{1.00} = 12.3\ 	ext{atm}$$

Study Guide: Gases and Intermolecular Forces (Chapters 10 & 11)

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