1. Chapter 11
Gas Laws

2. Elements that exist as gases at 250C and 1 atmosphere

3. Physical Characteristics of Gases
Gases assume the volume and shape of their containers.
Gases are the most compressible state of matter.
Gases will mix evenly and completely when confined to the same container.
Gases have much lower densities than liquids and solids.

4. Pressure is Measured in Units of:
Force
Area
Barometer
What is Pressure?
Pressure =
Pressure is Measured in Units of:
Pascals (Pa), millimeters of mercury, (mmHg), torr (torr), atmosphere (atm), and pounds of square inch (psi)

5. STP
To compare volumes of gases, one must know temperature and pressure at which the volumes are measured.
Scientists have agreed upon standards conditions of exactly 1 atm pressure and 0 degrees celsius (273K).

6. 1 atmosphere of pressure = 760 mmHg
Under STP:
1 atmosphere of pressure = 760 mmHg
1atm = 760 torr
1 atm = kPa
1atm = 14.7psi

7. The average atmospheric pressure at sea level is 0°C
The average atmospheric pressure at sea level is 0°C. Basically the weight of air at sea level is equal to 1 atm. What happens to atm pressure as you move further away from sea level?
10 miles
0.2 atm
4 miles
0.5 atm
Sea level
1 atm

8. A Barometer is an instrument used to measure atmospheric pressure

9. Convert Units of Pressure:
Example #1:
Express atm in units of mmHg and kPa
0.830 atm x mmHg = 631 mmHg
1 atm
0.830 atm x kPa = kPa
1 atm

10. Dalton’s Law of Partial Pressures
In a mixture of gases, the total pressure is calculated by adding the pressure of each individual gas in the mixture.
V and T are constant P1 P2
Ptotal = P1 + P2

11. Pg. 367 #1-4 1. Force / Area 2. mmHg, torr, kPa, psi, atm
3. STP = 273K and 1 atm
4. a) kPa x 1 atm = atm
101.3kPa
b) 456 torr x atm = x 10-1 atm
760 torr

12. Boyle’s Law

13. What is Boyle’s Law?
Boyle’s Law states that when a gas is under pressure it takes up less space:
Boyles Law tells us about the relationship between the volume of a gas and its pressure at a constant temperature. The higher the pressure, the smaller the volume.

14. VIDEO

15. Volume vs. Pressure Inverse Relationship

16. Sample Problem:
A deep sea diver is working at a depth where the pressure is 3.0 atmospheres. He is breathing out air bubbles. The volume of each air bubble is 2 cm3. At the surface the pressure is 1 atmosphere. What is the volume of each bubble when it reaches the surface?

17. BOYLE’S LAW
Figure out which variables the problems deals with (Volume and Pressure only)
Use the Combined Gas Law Formula (Refer to reference sheet)
Ignore the Temperature in the Formula
P1V1= P2V2
T T2

18. How we work this out: This is the formula we are going to use:
Formula first: P1 x V1 = P2 x V2
(Refer to reference Page)
Given:= P1 = 3.0 atm
V1 = 2 cm3
P2 = 1.0 atm
Unknown: V2

19. Here’s what you should have calculated
P1 x V1 = P2 x V2
3 atm x 2 cm3 = 1 atm x V2
6 = 1 (V2)
V2= 6 cm3

20. The Temperature-Volume Relationship
Charles’ Law
The Temperature-Volume Relationship

21. Charles’ Law
French chemist Jacques Charles discovered that the volume of a gas at constant pressure changes with temperature.
Temperature and volume are directly related……As the temperature of the gas increases, so does its volume, and vie versa

22. VIDEO

23. Volume vs. Temperature Direct Relationship

24. Example
If the temperature of a given amount of gas is doubled, for example, its volume will also double (as long as pressure remains unchanged).

25. Charles’ Law Example Problem:
A sample of neon gas occupies a volume of 752 mL at 25°C. What volume will the gas occupy at 50°C if the pressure remains constant?
Given:
V1 = 752 mL
T1 = 25°C = 298K
T2 = 50°C = 323K

26. Charles’ Law
Determine which variables are in the problem.
Delete the variable that is not in the problem. (Pressure) That means that pressure remains constant.
Use the Combined Gas Law to extrapolate the right equation to solve this problem (reference sheet)
P1V1 = P2V2
T T2

27. Equation Used:
V1 = V2
T1 T2
752 mL = V2
298 K K
298K = mL
V2 = 815 mL

28. Gay-Lussac’s Law

29. What is Gay-Lussac’s Law?
Gay-Lussac’s Law states that when a gas is under constant volume, there is a direct relationship between temperature and pressure.
The higher the temperature, the higher the pressure.

30. 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 is constant.
An increase in temperature increases the pressure of a gas. 30

31. PRESSURE VS. TEMP

32. 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?
Which variable is constant? 32

33. Gay-Lussac’s Law P1 V1 = P2 V2 T1 T2 Used the Combined Gas Law
When you have problems that give you volume and pressure.
Delete Volume in the Equation
P1 V1 = P2 V2
T T2

34. Gay-Lussac’s Law P1 = P2 T1 T2
This formula is used when the volume is constant.
P1 = P2
T T2

35. UNIVERSAL GAS CONSTANT
Ideal Gas Law
PV=nRT
UNIVERSAL GAS CONSTANT
R= Latm/molK
R=8.315 dm3kPa/molK

36. Ideal Gas Law P = ? atm PV = nRT n = 0.412 mol T = 16°C = 289 K
Calculate the pressure in atmospheres of mol of He at 16°C & occupying 3.25 L.
GIVEN:
P = ? atm
n = mol
T = 16°C = 289 K
V = 3.25 L
R = Latm/molK
WORK:
PV = nRT
P(3.25)=(0.412)(0.0821)(289)
L mol Latm/molK K
P = 3.01 atm