1. General, Organic, and Biological Chemistry
Fourth Edition
Karen Timberlake
Chapter 7
Gases
7.1
Properties of Gases
Lectures
© 2013 Pearson Education, Inc.

2. Common Gases Of the elements on the periodic table, some exist as a
gas 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. 2

3. Gases and Environmental Concerns
Some gases are responsible for environmental and
health 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 3

4. 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. 4

5. 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

6. Gas Pressure Gas pressure is the force acting on a specific area.
has units of atm, mmHg, torr, lb/in.2, and kilopascals(kPa).
1 atm = mmHg (exact)
1 atm = 760 torr (exact)
1 atm = lb/in.2
1 atm = kPa 6

7. 1. Pressure and Volume Relationship
General, Organic, and Biological Chemistry
Fourth Edition
Karen Timberlake
The Original Gas Laws
1. Pressure and Volume Relationship
(Boyle’s Law)
© 2013 Pearson Education, Inc.

8. 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. 8

9. PV Constant 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) 9

10. Guide to Using Gas Laws 10

11. 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

12. 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 2 Rearrange the gas law equation to solve for the unknown quantity.
P1V1 = P2V Boyle’s Law
To solve for V2 , divide both sides by P2. 12

13. 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 3 Substitute values into the gas law equation and calculate. 13

14. 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. 14

15. 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

16. 2. Temperature and Volume Relationship
General, Organic, and Biological Chemistry
Fourth Edition
Karen Timberlake
The Gas Laws
2. Temperature and Volume Relationship
(Charles’ Law)
© 2013 Pearson Education, Inc.

17. 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

18. Charles’s Law: V and T
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. 18

19. Charles’s Law: V and T
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 and
final conditions.
Analyze the Problem.
Conditions 1
Conditions 2
Know
Predict
T1 = 12 °C = 285
T1 = 32 °C+ 273
= 305 K
T increases
V1 = 3.1 L
V1 = ?
V increases 19

20. Charles’s Law: V and T
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 solve
for the unknown quantity. 20

21. Charles’s Law: V and T
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 equation
and the table. 21

22. 3. Temperature and Pressure Relationship
General, Organic, and Biological Chemistry
Fourth Edition
Karen Timberlake
The Gas Laws
3. Temperature and Pressure Relationship
(Gay-Lussac’s Law)
© 2013 Pearson Education, Inc.

23. 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

24. 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 K
T increase 24

25. 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

26. 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. 26

27. General, Organic, and Biological Chemistry
Fourth Edition
Karen Timberlake
The Combined Gas Law
© 2013 Pearson Education, Inc.

28. Combined Gas Law The combined gas law uses Boyle’s Law, Charles’s
Law, and Gay-Lussac’s Law (n is constant). 28

29. 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

30. Using the Combined Gas Law
A L sample of gas has a pressure of 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.
Conditions 1
Conditions 2
P1 = atm
P2 = 3.20 atm
V1 = L
V2 = 90.0 mL= L
T1 = 29 °C = 302 K
T2 = ? 30

31. Using the Combined Gas Law
A L sample of gas has a pressure of 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. 31

32. Using the Combined Gas Law
A L sample of gas has a pressure of 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.

33. Learning Check
A gas has a volume of 675 mL at 35 °C and atm pressure. What is the volume (mL) of the gas at −95 °C and a pressure of 802 mmHg (n constant)? 33

34. Solution
A gas has a volume of 675 mL at 35 °C and 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 final
conditions.
Analyze the Problem. 34

35. Solution
A gas has a volume of 675 mL at 35 °C and 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 for
the unknown quantity. 35

36. Solution
A gas has a volume of 675 mL at 35 °C and 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 equation
and calculate. 36