Q: A mixture contains 2.0 mol of $$O_2$$ and 3.0 mol of $$N_2 in a 5.0 L $$container at 300 K. What is the partial pressure of $$O_2$$? ($$R = 0.0821\ \mathrm{L\cdot atm\cdot $$mol^{-1}$$\cdot K$$^{-1}$$})$$

$$P_{O_2$} = \dfrac{nRT}{V} = \dfrac{2.0 \times 0.0821 \times 300}{5.0} = 9.85\ \mathrm{atm}$$

Q: A 5.00 g sample of an unknown gas occupies 2.50 L at 1.00 atm and 300 K. What is the molar mass of the gas? ($$R = 0.0821\ \mathrm{L\cdot atm\cdot $$mol^{-1}$$\cdot K$$^{-1}$$})$$

$$M = \dfrac{mRT}{PV} = \dfrac{5.00 \times 0.0821 \times 300}{1.00 \times 2.50} = 49.3\ \mathrm{g\cdot $$mol^{-1}$$}$$

Question 1

Ice cores are used to study Earth's ancient atmosphere. Which of the following best explains how scientists determine the age of gases trapped in different layers of an ice core?

Accepted Answer

By analyzing the depth of the ice, since glaciers form with newer ice on top and older ice deeper down.

Question 2

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

Accepted Answer

Gas particles lose energy during elastic collisions with each other.

Question 3

Which of the following best describes how the distribution of molecular speeds in a gas changes as temperature increases?

Accepted Answer

The distribution becomes broader and shifts to higher speeds.

Question 4

A sample of nitrogen gas ($$N_2) is $$contained in a 10.0 L vessel at 2.00 atm and 300 K. How many moles of $$N_2$$ are present? Use $$R = 0.0821\ \mathrm{L\cdot atm\cdot $$mol^{-1}$$\cdot K$$^{-1}$$}.$$

Accepted Answer

$$n = \dfrac{(2.00)(10.0)}{(0.0821)(300)} = 0.812\ \mathrm{mol}$$

Question 5

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

Accepted Answer

Ammonia ($$NH_3)$$

Question 6

Which of the following best explains why hurricanes strengthen over warm ocean waters?

Accepted Answer

Warm water increases the density of water vapor, providing more latent heat energy for the storm.

Question 7

Which of the following correctly ranks the intermolecular forces present in small molecules from weakest to strongest?

Accepted Answer

Dispersion \u003c Dipole-dipole \u003c Hydrogen bonding

Question 8

A mixture contains 2.0 mol of $$O_2$$ and 3.0 mol of $$N_2 in a 5.0 L $$container at 300 K. What is the partial pressure of $$O_2$$? ($$R = 0.0821\ \mathrm{L\cdot atm\cdot $$mol^{-1}$$\cdot K$$^{-1}$$})$$

Accepted Answer

$$P_{O_2$} = \dfrac{nRT}{V} = \dfrac{2.0 	imes 0.0821 	imes 300}{5.0} = 9.85\ \mathrm{atm}$$

Question 9

Which of the following statements about dispersion forces is TRUE?

Accepted Answer

Dispersion forces increase with increasing molecular size.

Question 10

Which of the following best describes the relationship between vapor pressure and the strength of intermolecular forces?

Accepted Answer

Stronger intermolecular forces result in lower vapor pressure.

Question 11

A 5.00 g sample of an unknown gas occupies 2.50 L at 1.00 atm and 300 K. What is the molar mass of the gas? ($$R = 0.0821\ \mathrm{L\cdot atm\cdot $$mol^{-1}$$\cdot K$$^{-1}$$})$$

Accepted Answer

$$M = \dfrac{mRT}{PV} = \dfrac{5.00 	imes 0.0821 	imes 300}{1.00 	imes 2.50} = 49.3\ \mathrm{g\cdot $$mol^{-1}$$}$$

Question 12

Which of the following is an application of the enthalpy of vaporization ($$\Delta H_{vap}) of $$water in living systems?

Accepted Answer

It enables sweating to cool the human body through evaporation.

Question 13

Which of the following best describes a foam?

Accepted Answer

A dispersion of gas bubbles in a liquid or solid.

Question 14

A gas mixture contains 1.0 mol $$He$$, 2.0 mol $$Ne$$, and 3.0 mol $$Ar. $$What is the mole fraction of $$Ne in $$the mixture?

Accepted Answer

$$\chi_{Ne} = \dfrac{2.0}{1.0+2.0+3.0} = 0.33$$

Question 15

Which of the following molecules exhibits dipole-dipole interactions but does NOT form hydrogen bonds?

Accepted Answer

Chloromethane ($$CH_3Cl)$$

Question 16

A 2.00 L container holds 0.500 mol of $$CO_2 at 400 K. $$What is the pressure inside the container? ($$R = 0.0821\ \mathrm{L\cdot atm\cdot $$mol^{-1}$$\cdot K$$^{-1}$$})$$

Accepted Answer

$$P = \dfrac{nRT}{V} = \dfrac{0.500 	imes 0.0821 	imes 400}{2.00} = 8.21\ \mathrm{atm}$$

Question 17

Which of the following best explains why the isotopic composition of gases in ice cores is useful for reconstructing past temperatures?

Accepted Answer

The distribution of isotopes in water vapor depends on temperature, affecting the isotopic composition of ice formed.

Question 18

Which of the following is the correct unit conversion for pressure from 1 atm to mmHg?

Accepted Answer

1 atm = 760 mmHg

Question 19

Which of the following best describes how vapor pressure is measured?

Accepted Answer

By measuring the pressure exerted by a vapor in equilibrium with its liquid in a closed container.

Chemistry 1770 Final Study Guide: Gases and Intermolecular Forces

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