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© 2013 Pearson Education, Inc. Chapter 7, Section 1

General, Organic, and Biological Chemistry

Fourth Edition

Karen Timberlake

7.1Properties of Gases

Chapter 7Gases

© 2013 Pearson Education, Inc.Lectures

© 2013 Pearson Education, Inc. Chapter 7, Section 1

Common Gases

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Of the elements on the periodic table, some exist as agas at room temperature, these include

� the Noble Gases, Group 8A (18),

� H2, N2, O2, F2, Cl2, and

� many oxides of nonmetals such as CO, CO2, NO, NO2, SO2, and SO3.

© 2013 Pearson Education, Inc. Chapter 7, Section 1

Gases and Environmental

Concerns

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Some gases are responsible for environmental andhealth concerns including

� methane, CH4,and carbon dioxide, CO2 � both greenhouse gases involved in climate change

� chlorofluorocarbons (CFCs) � involved in depleting the ozone layer, which filters out UV light reaching Earth,

� nitrogen oxides found in smog (respiratory irtitants), and

� volatile organic compounds (VOCs), such as compounds found in paint thinners, plastics, industrial solvents, pesticides

© 2013 Pearson Education, Inc. Chapter 7, Section 1

Kinetic Theory of Gases

A gas consists of small particles that

� move randomly with high velocities.

� have essentially no attractive (or repulsive) forces toward each other.

� have a very small volume compared to the volume of the containers they occupy.

� are in constant motion.

� have kinetic energies that increase with an increase in temperature.

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© 2013 Pearson Education, Inc. Chapter 7, Section 1

Properties of Gases

Gases are described in terms of four properties:

1. pressure (P),

2. volume (V),

3. temperature (T), and

4. amount (n).

5 © 2013 Pearson Education, Inc. Chapter 7, Section 2

Gas pressure

� is the force acting on a specific area.

� has units of atm, mmHg, torr, lb/in.2, and kilopascals(kPa).

1 atm = 760 mmHg (exact)

1 atm = 760 torr (exact)

1 atm = 14.7 lb/in.2

1 atm = 101.325 kPa

Gas Pressure

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© 2013 Pearson Education, Inc. Chapter 7, Section 3

General, Organic, and Biological Chemistry

Fourth Edition

Karen Timberlake

1. Pressure and Volume Relationship

(Boyle’s Law)

The Original Gas Laws

© 2013 Pearson Education, Inc.

© 2013 Pearson Education, Inc. Chapter 7, Section 3

Boyle’s Law –oldest gas law

Boyle’s law states that

� the pressure of a gas is inversely related to its volume when temperature (T) and amount of gas (n) are constant.

� if the pressure (P) increases, then the volume (V) decreases.

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© 2013 Pearson Education, Inc. Chapter 7, Section 3

In Boyle’s law,

� the product P × V is constant as long as T and n do not change.

� it can be stated that since P × V is a constant.P1V1 = P2V2 (T, n constant)

PV Constant in Boyle’s Law

9 © 2013 Pearson Education, Inc. Chapter 7, Section 3

Guide to Using Gas Laws

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© 2013 Pearson Education, Inc. Chapter 7, Section 3

Solving for a Gas Law Factor

A sample of nitrogen gas (N2) has a volume of 4.2 L at 1.0 atm. If the pressure is decreased to 0.75 atm with no change in the temperature or amount of gas, what will be the new volume?Step 1 Organize the data in a table of initial and

final conditions.Analyze the Problem.

Factors T and n remain constant.

Conditions 1 Conditions 2 Know Predict

V1 = 4.2 L V2 = ? V increases

P1 = 1.0 atm P2 = 0.75 atm P decreases

11 © 2013 Pearson Education, Inc. Chapter 7, Section 3

Solving for a Gas Law Factor

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A sample of nitrogen gas (N2) has a volume of 4.2 Lat 1.0 atm. If the pressure is decreased to 0.75 atmwith no change in the temperature or amount ofgas, what will be the new volume?Step 2 Rearrange the gas law equation to solve

for the unknown quantity.P1V1 = P2V2 Boyle’s Law

To solve for V2 , divide both sides by P2.

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© 2013 Pearson Education, Inc. Chapter 7, Section 3

Solving for a Gas Law Factor

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A sample of nitrogen gas (N2) has a volume of 4.2 Lat 1.0 atm. If the pressure is decreased to 0.75 atmwith no change in the temperature or amount ofgas, what will be the new volume?

Step 3 Substitute values into the gas law equation and calculate.

© 2013 Pearson Education, Inc. Chapter 7, Section 3

Boyle’s Law and Breathing:

Inhalation

During inhalation,

� the lungs expand,

� the pressure in the lungs decreases, and

� air flows towards the lower pressure in the lungs.

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© 2013 Pearson Education, Inc. Chapter 7, Section 3

Boyle’s Law and Breathing:

Exhalation

During exhalation,

� lung volume decreases,

� pressure within the lungs increases, and

� air flows from the higher pressure in the lungs to the outside.

15 © 2013 Pearson Education, Inc. Chapter 7, Section 4

General, Organic, and Biological Chemistry

Fourth Edition

Karen Timberlake

The Gas Laws

© 2013 Pearson Education, Inc.

2. Temperature and Volume Relationship

(Charles’ Law)

© 2013 Pearson Education, Inc. Chapter 7, Section 4

Charles’s Law

Charles’s law states that,

� the Kelvin temperature of a gas is directly related to the volume of the gas,

� P and n are constant, and

� as the temperature of a gas increases, the molecules move faster and its volume increases to maintain constant P.

17 © 2013 Pearson Education, Inc. Chapter 7, Section 4

Charles’s law states that when the temperature of a gas increases, making the molecules move faster, the volume of the gas must increase to maintain constant pressure.

Charles’s Law: V and T

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© 2013 Pearson Education, Inc. Chapter 7, Section 4

A sample of neon gas has a volume of 3.1 L and a temperature of 12 ˚C. Find the new volume (L) of the gas if the temperature rises to 32 ˚C. Assume the pressure and amount of gas remain constant.

Step 1 Organize the data in a table of initial andfinal conditions.

Analyze the Problem.

Charles’s Law: V and T

Conditions 1 Conditions 2 Know Predict

T1 = 12 °C + 273

= 285

T1 = 32 °C+ 273

= 305 KT increases

V1 = 3.1 L V1 = ? V increases

19 © 2013 Pearson Education, Inc. Chapter 7, Section 4

A sample of neon gas has a volume of 3.1 L and a temperature of 12 ˚C. Find the new volume (L) of the gas if the temperature rises to 32 ˚C. Assume the pressure and amount of gas remain constant.

Step 2 Rearrange the gas law equation to solvefor the unknown quantity.

Charles’s Law: V and T

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© 2013 Pearson Education, Inc. Chapter 7, Section 4

A sample of neon gas has a volume of 3.1 L and a temperature of 12 ˚C. Find the new volume (L) of the gas if the temperature rises to 32 ˚C. Assume the pressure and amount of gas remain constant.

Step 3 Substitute values into the gas law equationand the table.

Charles’s Law: V and T

21 © 2013 Pearson Education, Inc. Chapter 7, Section 5

General, Organic, and Biological Chemistry

Fourth Edition

Karen Timberlake

3. Temperature and Pressure Relationship

(Gay-Lussac’s Law)

The Gas Laws

© 2013 Pearson Education, Inc.

© 2013 Pearson Education, Inc. Chapter 7, Section 5

Gay-Lussac’s Law: P and T

Gay-Lussac’s law states that

� the pressure exerted by a gas is directly related to the Kelvin temperature.

� V and n are constant.

� an increase in temperature increases the pressure of a gas.

23 © 2013 Pearson Education, Inc. Chapter 7, Section 5

Calculation with Gay-Lussac’s

Law

A gas has a pressure at 2.0 atm at 18 ˚C. What is the new pressure when the temperature is increased to 62 ˚C? (V and n constant)

Step 1 Organize the data in a table of initial and final conditions.

Analyze the Problem.

Conditions 1 Conditions 2 Know Predict

P1 = 2.0 atm P2 = ? P increase

T1 = 18 °C + 273

= 291 K

T2 = 62 °C + 273

= 335 KT increase

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© 2013 Pearson Education, Inc. Chapter 7, Section 5

Calculation with Gay-Lussac’s

Law

A gas has a pressure at 2.0 atm at 18 ˚C. What is the new pressure when the temperature is increased to 62 ˚C? (V and n constant)

Step 2 Rearrange the gas law equation to solve for the unknown quantity.

25 © 2013 Pearson Education, Inc. Chapter 7, Section 5

Calculation with Gay-Lussac’s

Law

A gas has a pressure at 2.0 atm at 18 ˚C. What is the new pressure when the temperature is increased to 62 ˚C? (V and n constant)

Step 3 Substitute values into the gas law equation and calculate.

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© 2013 Pearson Education, Inc. Chapter 7, Section 6

General, Organic, and Biological Chemistry

Fourth Edition

Karen Timberlake

The Combined Gas Law

© 2013 Pearson Education, Inc.

© 2013 Pearson Education, Inc. Chapter 7, Section 6

Combined Gas Law

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The combined gas law uses Boyle’s Law, Charles’sLaw, and Gay-Lussac’s Law (n is constant).

© 2013 Pearson Education, Inc. Chapter 7, Section 6

Combined Gas Law

By using the combined gas law, we can derive any of the gas laws by omitting those properties that do not change.

29 © 2013 Pearson Education, Inc. Chapter 7, Section 6

A 0.180 L sample of gas has a pressure of 0.800 atm at 29 °C. At what temperature (°C) will the gas have a volume of 90.0 mL and a pressure of 3.20 atm (n constant)?

Step 1 Organize the data in a table of initial and final

conditions.

Analyze the Problem.

Using the Combined Gas Law

Conditions 1 Conditions 2

P1 = 0.800 atm P2 = 3.20 atm

V1 = 0.180 L V2 = 90.0 mL= 0.0900 L

T1 = 29 °C + 273 = 302 K T2 = ?

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© 2013 Pearson Education, Inc. Chapter 7, Section 6

A 0.180 L sample of gas has a pressure of 0.800 atm at 29 °C. At what temperature (°C) will the gas have a volume of 90.0 mL and a pressure of 3.20 atm (n constant)?

Step 2 Rearrange the gas law equation to solve for

the unknown quantity.

Using the Combined Gas Law

31 © 2013 Pearson Education, Inc. Chapter 7, Section 6

A 0.180 L sample of gas has a pressure of 0.800 atm at 29 °C. At what temperature (°C) will the gas have a volume of 90.0 mL and a pressure of 3.20 atm

(n constant)?

Step 3 Substitute values to solve for unknown.

Using the Combined Gas Law

© 2013 Pearson Education, Inc. Chapter 7, Section 6

A gas has a volume of 675 mL at 35 °C and 0.850 atm pressure. What is the volume (mL) of the gas at −95 °C and a pressure of 802 mmHg (n constant)?

Learning Check

33 © 2013 Pearson Education, Inc. Chapter 7, Section 6

A gas has a volume of 675 mL at 35 °C and 0.850 atm pressure. What is the volume (mL) of the gas at −95 °C and a pressure of 802 mmHg (n constant)?

Step 1 Organize the data in a table of initial and finalconditions.

Analyze the Problem.

Solution

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© 2013 Pearson Education, Inc. Chapter 7, Section 6

A gas has a volume of 675 mL at 35 °C and 0.850 atm pressure. What is the volume (mL) of the gas at −95 °C and a pressure of 802 mmHg (n constant)?

Step 2 Rearrange the gas law equation to solve forthe unknown quantity.

Solution

35 © 2013 Pearson Education, Inc. Chapter 7, Section 6

A gas has a volume of 675 mL at 35 °C and 0.850 atm pressure. What is the volume (mL) of the gas at −95 °C and a pressure of 802 mmHg (n constant)?

Step 3 Substitute values into the gas law equationand calculate.

Solution

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