1. Gases and the Gas Laws Mythbuster – cansI Intro to gas laws
Chapter 13
Gases and the Gas Laws
Mythbuster – cansI
Intro to gas laws

2. Gas Laws in Action: workers steam cleaned this tanker car and then sealed up the container, they came back the following morning to this disaster. (video)

3. Kinetic Theory Assumptions for an Ideal Gas
Gas particles are in constant, random motion
Gas particles themselves have virtually no volume
Gas particles do not attract nor repel each other
No kinetic energy is lost when particles collide
If gases are at the same temp. they have the same KE

4. NOTE:
Real gases (actual gases) do NOT obey all the assumptions made by the kinetic theory (only ideal gases behave this way- we will get exceptions later)

5. Factors (variables) that Affect Gases
Number of gas particles present
Temperature
Pressure
Volume of the sample
Animation (explanation)
Animation changing each of the variables (graph)

6. In a tied off balloon the pressure from the outside = pressure from the inside (in this chapter we will look at how changing the factors, changes these values) =

7. STP Standard temperature and standard pressure
Standard temperature = 0° C (273 K)
Standard pressure = kPa (1 atm or 760 mm Hg)

8. Boyles Law
States that the volume of a gas is inversely proportional to its pressure if the temperature remains constant
As pressure goes up, volume goes down and vice versa if temperature is constant
PV = k

12. P V P x V P1= 1 atm V1= 800 ml 800 P2= 2 atm V2= 400 ml 800
So: P1V1 = P2V2
Boyles Law

13. If. 600 L (V1)of a gas at 100. 0 kPa (P1) changes to 62. 4 kPa
If .600 L (V1)of a gas at kPa (P1) changes to 62.4 kPa.(P2) What is the new volume if temperature remains constant?
P1V1 = P2V2
(100.0 kPa) (.600L) = (62.4 kPa) (V2)
L = V2
.962 L = V2

14. Note: you do not need to convert units as long as they match on both sides of the equation
A 185 ml sample has a pressure of 4.2 atm. What is it’s pressure when the volume is 250 ml if temperature remains constant?
P1V1 = P2V2
(4.2 atm)(185 ml) = P2 (250 ml)
3.1 atm = P2

15. Charles Law
Jacque Charles investigated the property of changing temperature on the volume of a gas (saw w/ each ° C change the volume changed by 1/273rd)
Charles Law – volume of a fixed mass of gas is directly proportional to its kelvin temperature if the pressure is constant
Ex. Helium balloon deflates when walking outside on a cold day

17. Charles Law: V1 = V2 V1T2 = V2T1 T1 T2 or
*** “T” must be in Kelvin ( K = C +273)

18. A balloon inflated in an air conditioned room at 28° C (T1) has a volume of 4.0 L (V1). If it is heated to a temperature of 58 °C ( T2), what is the new volume (V2) of the balloon if pressure remains constant?
V1 = V2
T T2
T1 = = 301K
T2 = = 331 K

19. V1T2 = V2 T1
(4.0 L ) (331 K) = V2
(301 K)
4.4 L = V2

20. Adjust the volume of 609 ml of a gas at 83°C to standard temperature.

21. Eggs and Gas Laws

22. Gay-Lussac’s Law
States that the pressure of a gas is directly proportional to the Kelvin temperature if volume is kept constant
Ex. Spray paint can (rigid container) in a bonfire
P1 = P2
T T2
P1T2 = P2T1 or
“T” must be in Kelvin

23. As temperature increases, pressure has to increase proportionately to keep same volume

24. The pressure of a gas in a tank is 3. 20 atm (P1) at 22. 0 °C (T1)
The pressure of a gas in a tank is 3.20 atm (P1) at 22.0 °C (T1). If the temperature is raised to 60.0 °C (T2), what is the new pressure (P2) if volume is held constant?
T1 = = 295 K
T2 = = 333 K

25. P1 = P2
T T2
P1T2 = P2 T1
(3.20 atm) (333K) = P2
295 K
3.61 atm = P2

26. The Combined Gas Law
Many times it is hard to keep a variable constant (and only deal with changing 2 variables at a time), so we have to use all the laws together
Combined Gas Law: all the variables of pressure, temperature and volume change (only thing that is constant is the number of particles)

27. P1V1 = P2V2
T T2 or
P1V1T2 = P2V2T1

28. Find the volume of a gas at STP if it measures 806 ml at 26
Find the volume of a gas at STP if it measures 806 ml at 26.0° C and kPa
P1V1 = P2V2
T T2
P1 = kPa
V1 = 806 ml
T1 = = 299 K
P2 = kPa (standard pressure)
V2 = ?
T2 = 273 K (standard temperature)

29. (103.0 kPa) (806 ml) = (101.3 kPa) (V2)
299 K K
(103.0 kPa) (806ml) (273 K) = V2
(299 K) (101.3 kPa)
748 ml = V2

30. Gases and the MOLE Rock me Avogadro
Avogadro’s Principle: at equal temperatures and equal pressures, equal volumes of gases contain the same number of molecules
Molar Volume: volume occupied by 1 mole of any gas under STP (0 °C, kPa) is 22.4 L (conversion factor= 22.4 L/1 mole)

31. O2 He
1 mole He at STP
6.02 x atoms He
4.00 g
22.4 L
1 mole O2 at STP
6.02 x molecules of O2
32.0 g
22.4 L

32. What is the volume of 8.6 g of Cl2 at STP?
Convert g  moles (molar mass)
Convert moles  volume (22.4 L/ mole 1)
.12 moles
8.6 g Cl2
1 mole Cl2
22.4 L 2)
71.0 g Cl2
1 mole
.12 moles
2.7 L

33. Ideal Gas
Combines Avogadro’s principle, Boyles, Charles and Gay-Lussac’s Law into a statement w/ P, V, T and # moles
Changing one variable will affect the other 3 variables
Ideal Gas Equation:
PV = nRT

35. PV = nRt
n = # of mole
R = Ideal Gas Constant ( experimentally determined constant based on Avogadro’s # and STP  dependent on unit used for pressure)

36. Pressure in: atm use: R= .0821 L· atm/ mole ·K
kPa use : R = L ·kPa/ mole· K
mm Hg use: R = 62.4 L· mm Hg/ mole ·K

37. Calculate the number of moles of gas contained in a 3
Calculate the number of moles of gas contained in a 3.0 L vessel at 30Ō K and a pressure of 1.50 atm.
PV = nRT
PV = n R= .0821 RT
(1.50 atm) (3.0 L) = n
(.0821 · 30ŌK)
n = .18 moles

38. Applying the Ideal Gas Law
Calculate molar mass:
n (# of moles) = mass of gas = m
Molar mass M
So: PV = nRT
PV = mRT or M
M = mRT PV

39. Calculate density: D= m/V M = mRT PV
(substitute D for m/v in this equation
M = DRT P
Or D = MP RT

41. Deviations from Ideal Behavior
Ideal Gases: have no attractive forces and do not take up space (volume)
Real Gases:
Occupy definite volume (take up space)- but volume is small
Under normal conditions real gases behave like ideal gases (follow all gas laws)

42. Under high pressures: particles are forced close together and can’t compress any further, also attractive forces take over
So: real gases will liquefy instead of disappearing like Boyle predicted
Same is true under really low temperatures

43. Gas Laws Test
Formulas, R values and periodic table will be given to you
> 40 questions
12 multiple choice
13 fill in the blank (need to know who did what law/PTV card/variables)
7 calculations (1 for each formula, 1 using 22.4 L= 1 mole, 1 PV= nRt)

44. Know: Who did each law What each law stands for
Scenerios with each law
Absolute zero
STP
Molar Volume /avogadros principle
Variables on a gas
Real gas vs ideal gas