2. What affects the behavior of a gas?
The number of particles present
Volume (the size of the container)
Temperature

3. Behavior of gas?? Usually refers to pressure But what is pressure?
Collisions between molecules & container
More collisions = higher pressure

4. Number of particles Assume same volume & temperature…
Increasing the number of particles will increase the number of collisions
Increased collisions means increased pressure

5. If you double the number of molecules
1 atm

6. If you double the number of molecules
You double the pressure.
2 atm

7. Number of particles
Decreasing the number of particles will decrease the number of collisions
Decreased collisions means decreased pressure

8. As you remove molecules from a container
4 atm

9. As you remove molecules from a container the pressure decreases
2 atm

10. As you remove molecules from a container the pressure decreases
Until the pressure inside equals the pressure outside
1 atm

11. UNDERSTANDING CHECK

12. Volume (the size of the container)
Assume constant number of particles & temperature
If the volume decreases, molecules have less room to move
More collisions = increased pressure

13. As the volume of a gas decreases,
1 atm
As the volume of a gas decreases,
4 Liters

14. As the volume of a gas decreases, the pressure increases
2 atm
2 Liters

15. Volume (size of the container)
If the volume increases, there is more room for the molecules to move
Fewer collisions = decreased pressure
SO… pressure and volume are INVERSELY related

16. UNDERSTANDING CHECK

17. Temperature Assume volume and number of particles are constant
Raising the temperature of a gas makes the particles move faster
Faster movement = more collisions = increased pressure
Decreasing temp = slower movement = less collisions = decreased pressure
DIRECT relationship

18. Start with 1 liter of gas at 1 atm pressure and 300 K Heat it to 600 K

19. Pressure will increase to 2 atm.
300 K
600 K
Pressure will increase to 2 atm.

20. 600 K
300 K (Start)
If volume not held constant, the volume will increase to 2 liters at 1 atm

21. What does that mean? Assume pressure is constant
Increasing the temperature will lead to an increase in volume
And thus decreasing the temperature will lead to a decrease in volume
Temperature & volume have a DIRECT relationship

22. UNDERSTANDING CHECK

23. Dalton’s Law of Partial Pressures
The total pressure inside a container is equal to the sum of the partial pressure of each gas.
The partial pressure of a gas is the pressure of that individual gas hitting the wall.
PTotal = P1 + P2 + P3 + …
For example…

24. We can find out the pressure in the fourth container…
By adding up the pressure in the first 3
2 atm
1 atm
3 atm
6 atm

25. Dalton’s Law of Partial Pressures
This means that we can treat gases in the same container as if they don’t affect each other.
We can figure out their pressures separately
And add them to get total pressure

26. Pressure measurements
Can use 3 different units
Kilopascals (kPa)
Atmospheres (atm)
Millimeters of mercury (mm Hg)
FYI…
1 atm = kPa = 760 mm Hg

27. Examples
What is the total pressure in a balloon filled with nitrogen & oxygen if the pressure of the oxygen is 170 mm Hg and the pressure of nitrogen is 620 mm Hg?

28. Examples
In a second balloon the total pressure is 1.3 atm. What is the pressure of oxygen if the pressure of nitrogen is 720 mm Hg?

29. Gas Laws
To make things easier, we are going to assume the gases behave ideally
Kinetic Molecular Theory
Gases particles are in a state of constant, random motion, moving in a straight line until they collide with another particle or the walls of the container.

30. Kinetic Molecular Theory
There is no attraction between gas particles or between the particles and the walls of the container.
Collisions between gas particles or collisions with the walls of the container are perfectly elastic. None of the energy of a gas particle is lost when it collides with another particle or with the walls of the container.

31. Kinetic Molecular Theory
IDEAL BEHAVIOR
Assume particles have no volume
Assume no attractive forces between molecules
Situation does not really exist but it...
makes the math easier
close approximation to reality

32. Boyle’s Law
At a constant temperature, pressure and volume are inversely related
As one goes up, the other goes down
P1V1 = P2V2

33. P V

34. Example
A balloon is filled with 25 L of air at 1.0 atm pressure. If the pressure is changed to 1.5 atm, what is the new volume?

35. Example
A balloon is filled with 73 L of air at 1.3 atm pressure. What pressure is needed to change to a volume of 43 L?

36. Charles’ Law
The volume of a gas is directly proportional to the Kelvin temperature if the pressure is held constant.
K = degrees Celsius (273.15)
V1 = V2 T T2

37. V T

38. Example
What is the temperature of a gas that is expanded from 2.5 L at 25ºC to 4.1L at constant pressure?

39. Example
What is the final volume of a gas that starts at 8.3 L and 17ºC and is heated to 96ºC?

40. Gay Lussac’s Law
The temperature and the pressure of a gas are directly related at constant volume.
P1 = P2 T T2

41. P T

42. A rigid container at 25C has a pressure of 430 kPa
A rigid container at 25C has a pressure of 430 kPa. What would the pressure be at 125 C?
A. 574 kPa
B. 320 kPa
C. 86 kPa
D kPa
E. 620 kPa

43. Examples
What is the pressure inside a L can of deodorant that starts at 25ºC and 1.2 atm if the temperature is raised to 100ºC?

44. Combined Gas Law
The Combined Gas Law deals with the situation where only the number of molecules stays constant.
Everything else varies
P1 V = P2 V2 T1 T2
Lets us figure out one thing when two of the others change.

45. The combined gas law contains all the other gas laws!
If the temperature remains constant. P1 x V1 P2 x V2 = T1 T2
Boyle’s Law

46. P1 x V1 P2 x V2 = T1 T2 Charles’ Law
The combined gas law contains all the other gas laws!
If the pressure remains constant. P1 x V1 P2 x V2 = T1 T2
Charles’ Law

47. P1 x V1 P2 x V2 = T1 T2 Gay-Lussac’s Law
The combined gas law contains all the other gas laws!
If the volume remains constant. P1 x V1 P2 x V2 = T1 T2
Gay-Lussac’s Law

48. Examples
A 15 L cylinder of gas at 4.8 atm pressure at 25ºC is heated to 75ºC and compressed to 17 atm. What is the new volume?

49. Examples
If 6.2 L of gas at 723 mm Hg at 21ºC is compressed to 2.2 L at 4117 mm Hg, what is the temperature of the gas?

50. Adding another variable
Avogadro’s Hypothesis – If T & P constant, 2 equal volumes of gas contain the same # of molecules
22.4 L = 1 mole = x 1023 molecules
Volume has a DIRECT relationship to number of moles present
More volume = more moles
Add this to the combined gas law

51. The Ideal Gas Law PV = nRT
Pressure (P) times Volume (V) equals the number of moles (n) times the Ideal Gas Constant (R) times the temperature in Kelvin (T).
Doesn’t compare 2 situations like other gas laws

52. The Ideal Gas Constant If pressure is in atm, R = 0.0821
If pressure is in mm Hg, R = 62.4
If pressure is in kPa, R = 8.31

53. Example
How many moles of air are there in a 2.0 L bottle at 19ºC and 747 mm Hg?

54. Example
What is the pressure exerted by 1.8 g of H2 gas in a 4.3 L balloon at 27ºC?