1. Chapter 14 The Behavior of Gases
Did you hear about the chemist who was reading a book about Helium? 
He just couldn't put it down.

2. OBJECTIVES: 14.1 Properties of Gases
Explain why gases are easier to compress than solids or liquids are
Describe the three factors that affect gas pressure

3. Gases can ______ to fill its container, unlike solids or liquids
Compressibility
Gases can ______ to fill its container, unlike solids or liquids
The reverse is also true:
They are easily compressed, or squeezed into a smaller volume
Compressibility is a measure of how much the ______ of matter decreases under _________

4. Compressibility
This is the idea behind placing air bags in automobiles
In an accident, the air compresses more than the steering wheel or dash when you strike it
The impact forces gas particles closer together, which is possible because there is a ___________between them

5. Compressibility
At __oC, the distance between particles is about 10x the diameter of the particle
Fig. 14.2
Shows spacing between
O2 and N2 molecules
in air
This empty space makes gases good _________
down & fur keep animals warm because the air ________ in them prevents heat from escaping the animal’s body)
How does the volume of the particles in a gas compare to the overall volume of the gas (kinetic theory)?

6. Variables that describe a Gas
The four variables and their common units:
1. ________ (P) in kilopascals
2. volume (V) in Liters
3. temperature (T) in Kelvin
4. ______ (n) in moles
The amount of gas, volume, and temperature are factors that affect gas pressure.

7. 1. Amount of Gas
When we inflate a balloon, we are adding gas molecules.
Increasing the number of gas particles increases the number of _______
thus, pressure increases
If temperature is constant, then doubling the number of particles doubles the ________

8. Pressure and the number of molecules are directly related
More molecules means more _______, and…
Fewer molecules means ______ collisions.
Gases naturally move from areas of high pressure to _____ pressure, because there is empty space to move into

9. Using Gas Pressure A practical application is aerosol (spray) cans
gas moves from higher pressure to lower pressure
a _______ forces the product out
whipped cream, hair spray, paint
Fig. 14.5, page 416
Is the can really ever “empty”?

10. 2. Volume of Gas
In a smaller container, the molecules have _____ room to move.
The particles hit the _____ of the ________ more often.
As volume decreases, pressure increases. (syringe example)
Thus, volume and pressure are ________ related to each other

11. 3. Temperature of Gas
Raising the temperature of a gas increases the pressure, if the volume is held _________. (T and P are directly related)
The faster moving molecules hit the walls harder, and more frequently!
Should you throw an aerosol can into a fire?
When should your automobile tire pressure be checked?

12. 14.2 The Gas Laws
OBJECTIVES:
Describe the relationships among the temperature, pressure, and volume of a gas
Use the combined gas law to solve problems

13. The Gas Laws are mathematical
The gas laws will describe HOW gases behave.
Gas behavior can be predicted by the _______.
The ______________ can be calculated with mathematical equations.
You need to know both of these: the theory, and the math

14. Don’t you love my swell scarf??
Robert Boyle ( )
Boyle was born into an aristocratic _____ family
Became interested in ______ and the new science of Galileo and studied chemistry. 
A founder and an influential fellow of the Royal Society of London
Wrote extensively on science, philosophy, and theology.
Don’t you love my swell scarf??

15. As volume increases, pressure decreases An inverse relationship!
#1. Boyle’s Law
Gas pressure is ________ proportional to volume, at a constant _________ (Check out this cool animation)
Pressure x Volume = a constant
Equation: P1V1 = P2V2 (at a constant T)
As volume increases, pressure decreases
An inverse relationship!

16. - Page 419

17. Jacques Charles ( )
French Physicist
Part of a scientific balloon flight in 1783 – one of three passengers in the second balloon ascension that carried humans
This is how his interest in gases started
It was a _________ filled balloon – good thing they were careful!

18. Charles’ Law Animation
For a fixed ____ (moles), gas volume is directly proportional to the _____ temperature, when pressure is _______.
This extrapolates to zero volume at a temperature of zero Kelvin.
Charles’ Law Animation

19. Converting Celsius to Kelvin
Gas law problems involving temperature always require Kelvin temperature.
Kelvin = C + 273
°C = Kelvin - 273
and

20. - Page 421

21. Practice Problems 9-10
If a sample of gas occupies 6.80 L at 325oC, what will its volume be at 25oC if the pressure does not change?
Exactly 5.00 L of air at –50.0oC is warmed to 100.0oC. What is the new volume if the pressure remains constant?

22. Joseph Louis Gay-Lussac (1778 – 1850)
____ chemist and physicist
Known for his studies on the _________ properties of gases.
In 1804 he made balloon ascensions to study magnetic forces and to observe the composition and temperature of the air at different altitudes.

23. #3. Gay-Lussac’s Law
The pressure and Kelvin temperature of a gas are directly proportional, provided that the ________ remains constant.
How does a pressure cooker affect the time needed to cook food? (Note page 422)

24. Practice Problems 11-12
A sample of nitrogen gas has a pressure of 6.58 kPa at 539 K. If the volume does not change, what will the pressure be at 211 K?
The pressure in a car tire is 198 kPa at 27oC. After a long drive, the pressure is 225 kPa. What is the temperature of the air in the tire (assume the volume is constant).

25. #4. The Combined Gas Law
The combined gas law expresses the relationship between ______, volume and _________ of a fixed amount of gas.

26. Practice Problems 13-14 See Sample Problem 14.4, page 424 if needed
A gas at 155 kPa and 25oC has an initial volume of 1.00 L. The pressure of the gas increases to 605 kPa as the temperature is raised to 125oC. What is the new volume?
A 5.00 L air sample has a pressure of 107 kPa at – 50oC. If the temperature is raised to 102oC and the volume expands to 7.00 L, what will the new pressure be?

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

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

29. P1 x V1 P2 x V2 = T1 T2 _________ Law
The combined gas law contains all the other gas laws!
If the volume remains constant... P1 x V1 P2 x V2 = T1 T2
_________ Law

30. 14.3 Ideal Gases OBJECTIVES:
Compute the value of an unknown using the ____ gas law
Compare and contrast real an ideal gases

31. 5. The Ideal Gas Law #1 Equation: P x V = n x R x T
Pressure times Volume equals the number of moles (n) times the _________________ (R) times the Temperature in Kelvin.
R = ______ (L x kPa) / (mol x K)
The other units must match the value of the constant, in order to cancel out.
The value of R could change, if other units of measurement are used for the other values (namely pressure changes)

32. Units and the Ideal Gas Law
R = 8.31 L·kPa/K·mol (when P in kPa)
R = ______ L·atm/K·mol (when P in atm)
R = 62.4 L·mmHg/K·mol (when P in mmHg)
Temperature always in _______!!

33. The Ideal Gas Law
We now have a new way to count _____ (the amount of matter), by measuring T, P, and V. We aren’t restricted to only STP conditions:
P x V
R x T
n =

34. Practice Problems
A rigid container holds 685 L of He(g). At a temperature of 621 K, the pressure of the gas is 1.89 x 103 kPa. How many grams of gas does the container hold?
A child’s lungs hold 2.20 L. How many moles of air (mostly N2 and O2) do the lungs hold at 37oC and a pressure of 102 kPa.

35. Ideal Gases
We are going to assume the gases behave “ideally”- in other words, they obey the Gas Laws under all conditions of temperature and pressure
Ideal gases do not really exist, but it makes the math easier and is a very close approximation.
Particles have no volume? ______!
No attractive forces __________!

36. Ideal Gases There are no gases that are absolutely “ideal” however…
Real gases do behave “ideally” at
high temperature, and low pressure
Because under these conditions, the gas particles themselves are so far apart they take up a very small proportion of the gas’s volume and the IM forces are so weak that they can be ignored

37. Ideal Gas Law: Useful Variations
PV = nRT
Replace n with _________ mass
P x V = m x R x T M
m = mass, in grams
M = molar mass, in g/mol
Rearrange equation 1
Molar mass = M = m R T P V
n (moles) = mass (g)
molar mass (g/mol)

38. Using Density in Gas Calculations
______ is mass divided by volume m V
so, we can use a density value to give us two values needed in PV = nRT
Volume (usually 1 L) and…
-, if we know the _________, because we can calculate it
grams (from D) x 1 mole
grams
D =

39. Using Density in Gas Calculations
What is the pressure of a sample of CO2 at 25oC, with a density of 2.0 g/L?
PV = nRT  P =
V = 1 L, R = 8.31 L·kPa/mol·K
n = 2.0 g x 1 mole/44.0 g = mole
P = _____________________ = 113 kPa
1 L
nRT V

40. Real Gases
and
Ideal Gases

41. Ideal Gases don’t exist, because:
Molecules __ take up space
There ____ ________ forces between particles
- otherwise there would be no liquids

42. Real Gases behave like Ideal Gases...
When the molecules are far apart.
The molecules take up a very small percentage of the space
We can ignore the particle volume.
True at low pressures and/or high temperatures

43. Real Gases behave like Ideal Gases…
When molecules are moving fast
= _____________
Collisions are harder and ____.
Molecules are not next to each other very long.
__________ forces can’t play a role.

44. Real Gases do NOT Behave Ideally…
When temperature is very low
Because the low KE means particles may ________ with one another for longer periods of time, _______ weaker IM forces to have an effect
When the pressure are _____
Because the particles are _______ together more closely and thus occupy a much ________ percentage of the volume

45. 14.4 Gas Mixtures & Movements
OBJECTIVES:
Relate the total pressure of a mixture of gases to the partial pressures of its component gases
Explain how the molar mass of a gas affects the rate at which it diffuses and effuses

46. #7 Dalton’s Law of Partial Pressures
For a mixture of gases in a container,
PTotal = P1 + P2 + P
P1 represents the “___________”, or the contribution by that gas.
Dalton’s Law is useful in calculating the pressure of gases ________ over water – a common lab technique

47. Collecting a Gas over Water
A common lab technique for collecting and measuring a gas produced by a chemical reaction
The bottle is filled with water and inverted in a pan of water
As the gas is produced in a separate container, tubing is used to carry it to the bottle where it displaces the water in the bottle
When the level of the gas in the bottle is even with the water in the pan, the pressure in the bottle = atmospheric pressure
A graduated cylinder is often used to collect the gas (for ease of measuring the gas volume)
Gas being
produced
Atmospheric
pressure

48. Dalton’s Law of Partial Pressures
If the gas in containers 1, 2 & 3 are all put into the fourth, the pressure in container 4 = the ____ of the pressures in the first 3
2 atm
+ 1 atm
+ 3 atm
= _ atm 1 2 3 4

49. Practice Problems
Determine the total pressure of a gas mixture containing oxygen, nitrogen and helium: PO2 = 20.0 kPa, PN2 = 46.7 kPa, PHe = 20.0 kPa.
A gas mixture containing oxygen, nitrogen and carbon dioxide has a total pressure of 32.9 kPa. If PO2 = 6.6 kPa and PN2 = 23.0 kPa, what is the PCO2 ?

50. Diffusion and Effusion
Diffusion = molecules moving from areas of ____ to areas of ____ concentration
Is mathematical phenomenon caused by random movements of gas particles
Effusion = gas particles escaping through a tiny hole in a container
Both diffusion and effusion depend on the molar mass of the particle, which determines the _______ at a given ________ (= average KE)

51. Diffusion describes the mixing of gases
Molecules move from areas of high concentration to low concentration
A function of probability
Fig , p. 435
Two gases mix after the wall separating them is removed.

52. Effusion: a gas escapes through a tiny hole in its container
- balloons slowly lose air over time
Diffusion and effusion are explained by the next gas law: Graham’s

53. 8. Graham’s Law RateA MB RateB MA =
The rate of effusion and diffusion is inversely proportional to the square root of the molar masses (M) of the gases.
Relationship based on: KE = ½ mv2
At a given temperature (avg KE) larger molecules will have lower velocities

54. Graham’s Law Explained
Temperature is a measure of the average KE of the particles in a sample of matter
At a given temperature (say 25oC), the molecules of a lighter gas will be moving faster than molecules of a heavier one, so…
Faster-moving particles spread out faster!
Light Gas = N2 (mw = 28 g/mol)
Heavy Gas = CO2
(mw = 44 g/mol)
KE = ½ mv2

55. Graham’s Law
Sample: compare rates of effusion of Helium (He) with Nitrogen (N2) – p. 436
With effusion and diffusion, the type of particle is important:
Gases of lower molar mass diffuse and effuse faster than gases of higher molar mass.
Helium effuses and diffuses 2.7 times faster than nitrogen – thus, helium escapes from a balloon quicker than air, which is ~79% N2!