1. What is Pressure? Force of gas particles running into a surface.
It’s measured by a barometer

2. Pressure is measured by a Barometer
Pressure changes with altitude
Barometric pressure at sea level
is (1 atm) or 760 mm Hg

3. Pressure and Moles (# of Molecules)
If pressure is molecular collisions with the container…
As number of molecules increase, there will be more molecules to collide with the wall
THUS, collisions between molecules and the wall increase
Pressure increases
As # of moles increase, pressure increases
Think about blowing up a balloon!

4. # of Gas Particles vs. Pressure

5. Pressure & Volume
If pressure is molecular collisions with
the container…
As volume increases, molecules can travel farther before hitting the wall
THUS collision frequency between molecules & the wall decreases
Pressure decreases
As volume increases, pressure decreases.
Think about how your lungs work!

6. What is “Temperature”?
Temperature – measure of the average kinetic energy of the molecules
Energy due to motion
(Related to how fast the molecules are moving)
As KELVIN temperature increases, Average Kinetic Energy
Increases and Molecular motion increases

7. Pressure and Temperature
If temperature is related to molecular
motion…
and pressure is molecular collisions with the container…
As temperature increases, molecular motion increases
Thus collision frequency increases
Pressure increases
As temperature increases, pressure increases

8. Volume and Temperature
and volume is the amount of space the gas occupies…
If temperature is related to molecular motion…
As temperature increases, molecular motion increases
THUS molecules will move farther away from each other
Volume increases
As temperature increases, volume increases
Think of liquid nitrogen and the balloon.

9. Volume and Moles (# of Molecules)
As number of molecules increases, there will be more molecules to collide with the wall
Thus, collision frequency increases
Volume increases
As # of moles increase, volume increases

10. Pressure In Versus Out
A container will expand or contract until the pressure inside equals the atmospheric pressure outside
A bag of chips is bagged at sea level. What happens if the bag is then brought up to the top of a mountain or in an airplane.
Example:
The internal pressure of the bag at low altitude is high
At high altitude there is lower pressure
Lower
pressure
Higher
pressure
Lower
pressure
The internal pressure is higher than the external pressure.
The bag will expand in order to reduce the internal pressure.

11. When Expansion Isn’t Possible
Rigid containers cannot expand
Example:
An aerosol can is left in a car trunk in the summer. What happens?
The temperature inside the can begins to rise.
As temperature increases, pressure increases.
Lower
pressure
Higher
pressure
Can
Explodes!
The internal pressure is higher than the external pressure.
The can is rigid—it cannot expand, it explodes!

12. Air Pressure Crushing Cans

13. Air Pressure Crushing “Cans”
Another cool video

14. Section 2: Kinetic Molecular Theory(KMT):
explains gas behavior based upon the motion of molecules
based on an ideal gas
IDEAL gases are IMAGINARY gases that follow the assumptions of the KMT

15. Assumptions of the KMT
All gases are made of atoms or molecules that are in constant, rapid, random motion 1
The KELVIN temperature of a gas is proportional to the average kinetic energy of the particles 2 3
Gas particles are not attracted nor repelled from one another ***
All gas particle collisions are elastic (no kinetic energy is lost to other forms) 4 5
The volume of gas particles is so small compared to the space between the particles, that the volume of the particle itself is insignificant***Gases have no Volume!

16. So what is a “REAL” gas?
Real gases, (like nitrogen), will eventually condense into a liquid when the temperature gets too low or the pressure gets too high BECAUSE:
Assumption #3
Gas particles do have attractions and repulsions towards one another
Assumption #5
Gas particles do take up space

17. Real Gases Deviate from Ideal Gas Behavior when at HIGH pressure
The gas molecules are
compressed making the
volume they take up more
significant than if they
were spread out

18. Real Gases Deviate from Ideal Gas Behavior when at LOW temperature.
The lower kinetic
energy causes the
molecules to move
slower and
ATTRACTIVE
FORCES
that really exist start
to take effect

19. A Molecule’s POLARITY can cause a deviation from Ideal Gas Law behavior
Polar gases (HCl) deviate more than nonpolar gases (He or H2)- due to innate strong attractive forces of polar molecules

20. Gas Movement: Effusion vs Diffusion
Effusion –gas escapes from a tiny hole in the container
Effusion is why balloons deflate over time!

21. Diffusion –gas moves across a space from high to low concentration
Diffusion is the reason we can smell perfume across the room

22. Effusion, Diffusion & Particle Mass
How are particle size (mass) and these concepts related?
As particle size (mass) increases, the particles move
slower, and the rate of effusion/diffusion is lower
it takes them more time to find the hole or to go
across the room
As mass of the particles increases, rate of effusion and diffusion is lowered.

23. Rate of Diffusion & Particle MassH2
Watch as larger particles take longer to get to your nose
CO2

24. Section 3—Gas Laws
How can we calculate Pressure, Volume and Temperature of a gas?

25. Pressure Units 1 atm = 101300 Pa = 101.3 kPa = 760 mm Hg = 14.7 psi
Several units are used when describing pressure
Unit
Symbol
atmospheres
atm
Pascals, kiloPascals
Pa, kPa
millimeters of mercury
mm Hg
pounds per square inch
psi
1 atm = Pa = kPa = 760 mm Hg = 14.7 psi

26. Conversions Between Different Pressure Units
1 atm = 760 mmHg = kPa
Examples
Convert 654 mm Hg to atm
2.Convert 879 mm Hg to kPa
3.Convert 15.6 atm to kPa
654 mmHg x 1atm =
760 mmHg
.861 atm
879 mmHg x Kpa =
760 mmHg
117 Kpa
15.6 atm x Kpa =
1atm
1580 Kpa

27. Temperature Unit used in Gas Laws
Kelvin (K)– temperature scale with an absolute zero
Temperatures cannot fall below an absolute zero
Examples
Convert 15.6 °C into K
2. Convert 234 K into °C
= K
 289 K
°C = 234
-39 °C

28. Standard Temperature & Pressure (STP)
the conditions of:
1 atm (or the equivalent in another unit)
0°C (273 K)
Problems often use “STP” to indicate quantities…don’t forget this “hidden” information when making your list!

29. GAS LAWS: “Before” and “After”
This section has 5 gas laws which have “before” and “after” conditions.
For example:
P= Pressure
V= Volume
T=Temperature
n= moles(molecules)
1= initial amount
2= final amount

30. Boyle’s Law
Pressure Increases as Volume Decreases

31. Boyles’ Law
Volume & Pressure have an INVERSELY proportional when temperature and moles are held constant
P = pressure
V = volume
The two pressure units must match and the two volume units must match!
Example:
A gas sample is 1.05 atm when at 2.5 L. What volume is it if the pressure is changed to atm?

32. Boyles’ Law V2 = 2.7 L P1 = 1.05 atm V1 = 2.5 L P2 = 0.980 atm
***The two pressure units must match & the two volume units must match!
Example:
A gas sample is 1.05 atm when 2.5 L. What volume is it if the pressure is changed to atm?
P1 = 1.05 atm
V1 = 2.5 L
P2 = atm
V2 = ? L
V2 = 2.7 L

33. Boyles Law: Graph

34. Charles’ Law
Volume Increases as Temperature Increases

35. Charles’ Law
Volume & Temperature are DIRECTLY proportional when pressure and moles are held constant.
The two volume units must match
& temperature must be in Kelvin!
V = Volume
T = Temperature
What is the final volume if a 10.5 L sample of gas is changed from 25C to 50C?
Example:
Temperature needs to be in Kelvin!
25C = 298 K
V1 = 10.5 L
T1 = 25C
V2 = ? L
T2 = 50C
50C = 323 K

36. Charles’ Law V1 = 10.5 L T1 = 25.0C = 298 K V2 = ? L T2 = 50.0C
***The two volume units must match & temperature must be in Kelvin!
Example:
What is the final volume if a 10.5 L sample of gas is changed from 25C to 50C?
V1 = 10.5 L
T1 = 25.0C
V2 = ? L
T2 = 50.0C
= 298 K
= 323 K
V2 = 11.4 L

37. Charles Law: Graph

38. Gay-Lussac’s Law
Temperature decreases as Pressure decreases

39. Gay-Lussac’s Law
Pressure & temperature are DIRECTLY proportional when moles and volume are held constant
P = Pressure
T = Temperature
The two pressure units must match
and temperature must be in Kelvin!
Example:
A sample of hydrogen gas at 47C exerts a pressure of .329 atm. The gas is heated to 77C at constant volume and moles. What will the new pressure be?
Temperature needs to be in Kelvin!
P1 = .329 atm
T1 = 47C
P2 = ? atm
T2 = 77C
47C = 320 K
77C = 350 K

40. Gay-Lussac’ Law Example:
A sample of hydrogen gas at 47C exerts a pressure of .329 atm. The gas is heated to 77C at constant volume and moles. What will the new pressure be?
P1 = .329 atm
T1 = 47.0C
P2 = ? atm
T2 = 77.0C
= 320 K
= 350 K
P2 = .360 atm

41. Gay Lussac Law: Graph

42. Avogadro’s Law
Moles and Volume are directly proportional when temp. & pressure are held constant
V = Volume
n = # of moles of gas
The two volume units must match!
A sample with 0.15 moles of gas has a volume of 2.5 L. What is the volume if the sample is increased to 0.55 moles?
Example:

43. Avogadro’s Law
The two volume units must match!
A sample with 0.15 moles of gas has a volume of 2.5 L. What is the volume if the sample is increased to 0.55 moles?
Example:
n1 = 0.15 moles
V1 = 2.5 L
n2 = 0.55 moles
V2 = ? L
V2 = 9.2 L

44. Combined Gas Law Example:
P = Pressure
V = Volume
n = # of moles
T = Temperature
Each “pair” of units must match and
temperature must be in Kelvin!
Example:
What is the final volume if a 15.5 L sample of gas at 755 mmHg and 298 K is changed to STP?

45. Combined Gas Law
P = Pressure
V = Volume
T = Temperature
Moles is not mentioned so remove it from equation!
What is the final volume if a 15.5 L sample of gas at 755 mmHg and 298K is changed to STP?
Example:
STP is standard temperature (273 K) and pressure (1 atm)
P1 = 755 mmHg
V1 = 15.5 L
T1 = 298 K
P2 = 760mmHg
V2 = ? L
T2 = 273 K
V2 = 14.1 L

46. Why you really only need 1 of these
The combined gas law can be used for all “before” and “after” gas law problems!
For example, if volume is held constant, then
and the combined gas law becomes:

47. Transforming the Combined Law
Watch as variables are held constant and the combined gas law “becomes” the other 3 laws
Hold pressure and temperature constant
Avogadro’s Law
Hold moles and temperature constant
Boyles’ Law
Hold pressure and moles constant
Charles’ Law

48. Section 4—Other Gas Laws

49. Dalton’s Law
Each gas in a mixture exerts its own pressure called a partial pressure
Total Pressure = PT
Partial Pressure= P1, P2….

50. Dalton’s Law
Example: A gas mixture is made up of oxygen(2.3 atm) and nitrogen(1.7 atm) gases. What is the total pressure?
PT = 2.3 atm atm
= 4.0 atm

51. Modified Daltons Law When a gas is collected over water,
the total pressure
of the mixture collected
is a combination of
water vapor and the
gas you are collecting!
2KClO3 (s) KCl (s) + 3O2 (g)
PT = PO + PH O 2

52. Modified Dalton’s Law
Example: What is the pressure of the water vapor if the total pressure of the flask is 17.5 atm and the pressure of the oxygen gas is 16.1 atm?
17.5 = 16.1 atm + PH2O
=1.4 atm

53. The Ideal Gas Law (an“AT NOW”equation)
The volume of a gas varies directly with the number of moles and its Kelvin temperature
P = Pressure
V = Volume
n = moles
R = Gas Law Constant
T = Temperature
Choose the one with units that match your pressure units!
There are three possibilities for “R”!
Volume must be in Liters when using “R” to allow the unit to cancel!

54. The Ideal Gas Law
Example:
A sample with 0.55 moles of gas is at kPa and 27°C. What volume does it occupy?

55. The Ideal Gas Law
The Ideal Gas Law does not compare situations—it describes a gas in one situation.
A sample with 0.55 moles of gas is at kPa and 27°C. What volume does it occupy?
Example:
Chosen to match the kPa in the “P” above
n = 0.55 moles
P = kPa
T = 27°C = 300 K
V = ?
R = 8.31 L kPa / mole K
V2 = 13 L

56. The Ideal Gas Law Example 2:
What mass of hydrogen gas in grams is contained in a 10.0 L tank at 27°C and 3.50 atm of pressure?
n = ?
P = 3.50 atm
T = 27°C = 300 K
V = 10.0 L
R = L atm /mole K
n = 1.42 mol NOW CHANGE TO GRAMS
Chosen to match the atm in the “P” above
1.42 mol x 2.02 g = g
1 mol