1. Gases

2. Topic: Boyles & Charles Law
Unit: Gases
Topic: Boyles & Charles Law
Objectives: Day 1 of 3
To become familiar with units of pressure
To understand the inversely proportional relationship of Boyles Law
To understand the proportional relationship of Charles Law

3. Quickwrite: Answer one of the questions below in 2-3 sentences:
What do you think would have to the size of a balloon if it was brought from sea level up to lake Tahoe???
What do think would happen to the size of a balloon if we heated the molecules inside
In terms of heat and energy, what do think a temperature of Absolute zero means??

4. Pressure
A gas uniformly fills any container, is easily compressed, and mixes completely with any other gas
One of the most obvious properties of a gas is that it exerts pressure on it’s surroundings
For example, when you blow up a balloon, the air inside pushes against the elastic sides of the balloon and keeps it firm

5. Pressure
The gases most familiar to us form the earth’s atmosphere N2 & O2
The pressure exerted by this gaseous mixture that we call AIR can be dramatically by the following experiment:

6. Pressure:
What do you think made the can collapse?

7. 1 standard atmosphere = 1.00 atm = 760 mm Hg = 760 torr
Units of Pressure
When dealing with Gases, Scietists use several different units of pressure
One of units we use to measure atmospheric pressure is in millimeters of mercury
Throughout history, most barometers contained mercury, so one unit of pressure we use is mm Hg
A much more easier to use unit of pressure is the standard atmosphere
1 standard atmosphere = 1.00 atm = 760 mm Hg = 760 torr

8. What are the units of pressure?
1 standard atmosphere = 1.00 atm = 760 mm Hg = 760 torr
Or 1 atm mmHg
760 torr atm

9. Practice: The air pressure outside today is 960mm Hg
Covert this mm Hg into standard atmosphere
960 mm Hg
=1.2 atm
1 atm
Conversion Factor
760 mm Hg
_1 atm__
760 mmHg

10. Boyle’s Law
Boyle’s Law states the volume of a given sample of gas at a constant temperature changes inversely with the pressure
It is represented by the following equation:
P1V1 = P2V2

11. As Pressure increases, Volume decreases 1 atm 3 atm

12. What is Boyle’s Law
Law that states the _____ of a given sample of gas at a constant temperature changes inversely with pressure
In other words, if Volume goes ___ then pressure goes down or vice versa
Equation: P1V1 = P2V2
volume
Answer Bank
Volume Up
Down
Temperature
Energy
Pressure up

13. Boyle’s Law
Boyle’s law means that if we know the volume of a gas at a given pressure, we can predict the new volume if the pressure is changed (provided the temperature is not changed)
Consider the Equation P1V1 = P2V2
This equation tells us that we can calculate the new gas volume (V2) by multiplying the original volume (V) by the ratio of the original pressure (P1) to the final pressure (P2)

14. Practice: Write the question below:
Consider a 1.5 liter sample of gaseous freon at a pressure of 126 mm Hg. If the pressure is changed to 210 mm Hg at a constant temperature:
Will the volume of the gas increase or decrease?
What will be the new volume of the gas?

15. In this case, pressure is increasing from 126mm Hg to 210 mm Hg, so volume will decrease 126 mm Hg mm Hg

16. Practice: Remember, we are solving for V2
Solving for V2, we can arrange the equation: P1V1 = P2V2 into:
By plugging our values into the above equation, we can solve for V2
P1 = P2 =
V1 = V2 =
126 mm Hg
210 mm Hg
1.5 L
? L
V2 = (V1 )(P1 / P2 )
V2 = (1.5L)(126 mm Hg / 210 mm Hg )
V2 =
0.9 L

17. Charles’s Law
Charles’s Law states that the volume of a given sample of gas at constant pressure is directly proportional to the temperature in Kelvin's
It is given by the equation below:

18. What is Charles’s Law?
The _____of a given sample of gas at constant pressure is directly proportional to the ________in Kelvin's
In other words, if temperature goes up, then volume goes up, or vice versa
Equation:
volume
Answer Bank
Volume Up
Down
Temperature
Energy
Pressure
temperature

19. Practice:
A 2 liter sample of air is collected at 298 Kelvin (K) and then cooled to 278 K:
Does the volume increase or decrease?
Calculate the volume of the air at 278 K

20. If I decrease
temperature,
volume
decreases
298 K
278 K

21. Practice: Remember, we are solving for V2
Using Charles Law, we can solving for V2, by arranging the equation: into:
By plugging our values into the above equation, we can solve for V2
T1 = T2 =
V1 = V2 =
298 K
278 K
2.0 L
? L
V2 = (T2 )(V1 / T1 )
V2 = (278 K)(2.0L / 298 K )
V2 =
1.86 L

22. Charles’s Law
The solid lines are based on several different gases and how they behave as temperature is decreased
Where the line is dashed, these gases eventually liquefy
When we extend all of the lines extrapolate to zero volume at the same temperature (-273ºC)

23. Charles’s Law
This suggests that -273ºC is the lowest possible temperature
In fact, experiments have shown that all matter cannot be cooled below this temperature
This temperature is defined as absolute zero
A scientist by the named of Lord Kelvin recognized this and devised a whole new temperature scaled based on absolute zero
On the Kelvin temperature scale, 0 is the lowest possible temperature

24. Absolute Zero GAS A GAS B GAS C = extrapolation40
GAS A 35
GAS B 30 25
GAS C
Volume (measured in mL) 20 15 10 5 20 40 60 80
100
120
140
160
180
200
220
240
260
273
Absolute Zero!!!!
Temperature Measured Kelvins

25. What is absolute zero? The lowest possible ________on the Kelvin scale
At this temperature (0) particles of matter have no heat and potential ______(stop moving)
Temperature
Answer Bank
Volume Up
Down
Temperature
Energy
Pressure
energy

26. Practice: Convert 46 degrees Celsius to Kelvin's using the equation:
TCelsius = T Kelvin
Solve: plug in 46 degrees into the equation above
= T Kelvin
= 319 Kelvin

27. Standard Temperature and Pressure (STP)
When performing gas experiments, scientists often use a standard set of conditions
Standard Temperature and Pressure refer to a pressure of 1 atm and a temperature of 273 K
STP is a set of given conditions that exist at 1 atmopshere (ATM) of pressure and a temperature of 273 Kelvin or 0°Celsius

28. What is Standard Temperature and Pressure?
A set of given conditions that exist at ____of pressure and a temperature of _____ or 0°Celsius
1 atm
Answer Bank
Volume Up
Moles
Down
1 atm
Temperature
Pressure
273K
273K

29. Summarize: Describe the proportional relationship of Boyle’s law
Describe the inversely proportional relationship of Charles law:
What are some different units of pressure????
What are the units of STP????

30. Topic: Gay-Lussacs, Combined, and Ideal Gas Laws
Unit: Gases
Topic: Gay-Lussacs, Combined, and Ideal Gas Laws
Objectives: Day 2 of 3
To understand the proportional relationship of Gay-Lassacs Law
To understand how pressure, temperature, and volume are related using the combined gas law
To understand the behavior of an ideal gas and the equation PV=nRT

31. Quickwite: Answer one of the questions below in one or two sentences:
If you heat up a can of hairspray, how do you think it affects the pressure inside the bottle????
If you have a balloon with one mole of helium gas, and your add another mole of helium gas to your balloon, how do you think this affects the volume of your balloon?

32. Gay-Lussac’s Law
If volume is constant, Gay-Lussac showed that as temperature went up, so does pressure
This is a proportional relationship
Gay-Lussac’s Law states that gas pressure and gas temperature are directly proportional at a constant volume

33. What is Gay-lussacs Law?
The law that states that gas _______and gas temperature are directly proportional at a constant volume
In other words, if temperature goes up, then pressure goes up
Equation:
pressure
Answer Bank
Volume Up
Moles
Down
1 atm
Temperature
Pressure
273K

34. Practice:
A gas at 298K has a pressure of 1.5 atm. It is heated to 596 K. If volume does not change, what is the new pressure?
Arranging the equation for P2, we get:
By plugging our values into the above equation, we can solve for P2
P1 = P2 =
T1 = T2 =
1.5 atm
? atm
298 K
596 K
P2 = (T2 )(P1 / T1 )
P2 = (596 K)(1.5atm / 298 K )
P2 =

35. Combined Gas Law
The laws of Boyle, Charles, and Gay Lussac can be combine into one equation
This is called the combined gas law
Below is the combined gas law that shows how pressure, volume, and temperature are related
Remember the units must always match!

36. What is the Combined Gas Law?
The law that shows how gas pressure,_________, and temperature are related
It is a combination of Boyle, Charles, and Gay-Lussac
volume
Answer Bank
Volume Up
Moles
Down
1 atm
Temperature
Pressure
273K

37. Practice:
A gas has a volume of 15.3 Liters at 298K and 1.11atm. What is the volume at STP (standard temperature and pressure)?
Remember STP = 273K and 1 atm
Let’s consider what we know:
P1 = P2 =
V1 = V2 =
T1 = T2 =
1.11atm
1 atm
? L
15.3 L
298 K
273 K

38. Practice: Plugging your values into the combined gas law: We get:
P1 = P2 =
V1 = V2 =
T1 = T2 =
1.11atm
1 atm
Plugging your values into the combined gas law:
We get:
? L
15.3 L
298 K
273 K
_(1.11atm)(15.3L) = _(1.0atm)(V2)_
(298K) (273K)

39. If the quantity doubles, then so does the volume
Avogadro’s Law
If the amount of moles (quantity) of a gas is doubled then the volume is doubled
Volume is proportional to the number of moles
4 liters of gas
2 liters of gas
1 Mole
If the quantity doubles, then so does the volume
2 Mole

40. What is Avogadro’s law?
If the amount of _____(quantity) of a gas is doubled then the _____is doubled
Volume is proportional to the number of moles
moles
Answer Bank
Volume Up
Moles
Down
1 atm
Temperature
Pressure
273K
volume

41. Ideal Gas
The ideal gas equation defines the behavior of an ideal gas
Most gases obey this equation when at ideal conditions, (STP = 1 atm and 273 K)
An ideal gas is a hypothetical gas that exactly obeys the ideal gas law
PV = nRT
R is a constant and is always equal to Latm/Kmol
PV = nRT
Pressure
Volume
Moles
Constant
Temperature

42. What is an ideal gas?
A hypothetical gas that exactly obeys the ideal gas _____
(PV = nRT)
R is a _______ and is equal to __________
law
Answer Bank
gas
Ideal
law
constant
1 atm
Temperature
Pressure
Latm/Kmol
constant
Latm/Kmol

43. Practice:
If I have 4 moles of a gas at a pressure of 5.6 atm and a volume of 12 liters, what is the temperature?
Solving for T, we get the equation:
5.6 atm
4 moles
P = n =
V = R =
T =
12 L
Latm/Kmol
????
T = PV substituting our
nR values in we get: T = __(5.6 atm)(12.0 L)___
(4 mol)( Latm/Kmol)

44. Practice:
A sample of Hydrogen gas, (H2), has a volume of 8.56 liters at a temperature of 0º Celsius and a pressure of 1.5 atm. Calculate the number of moles of H2 present in this gas sample:
Solving for n, we get the equation:
1.5 atm ?
P = n =
V = R =
T =
8.56 L
Latm/Kmol
273 K
n = PV substituting our
RT values in we get: n = __(1.5 atm)(8.56 L)___
( Latm/Kmol)(273K)

45. Practice:
A sample of diborane gas has a pressure of atm at a temperature of -15ºC and volume of 3.48 liters. If conditions are changed so that the temperature is now 36ºC and the pressure is atm, what will be the new volume of the sample?

46. Practice: Note that the volume of n (moles) is not given
P1 = P2 =
V1 = V2 =
T1 = T2 =
0.454
0.616 atm
? L
3.48 L
258 K
309 K
Note that the volume of n (moles) is not given
This tells us that the quantity of diborane gas does not change, therefore we do not need to use n or the constant R
This will give us the combine gas law

47. Summarize:
When given moles use the _______gas law to solve the problem
When given pressure, temperature, or volume us the _______ gas law to solve the problem
If the quantity of a gas doubles, then so does its _______
Answer Bank
Charles’s
Boyles’s
volume
Combined
ideal
Gay-Lussac
pressure

48. Topic: Gas Stoichiometry & Kinetic Molecular Theory
Unit: Gases
Topic: Gas Stoichiometry & Kinetic Molecular Theory
Objectives: Day 3 of 3
To Understand the Molar Volume of a gas
To understand the basic assumptions of the kinetic molecular theory

49. Quickwrite: Answer one of the questions below in 2-3 sentences:
Review: If you have a mole of oxygen molecules, then how many molecules do you have????
Do you think gas particles ever stop moving?
If you heat up gas particles, do you think they move faster or slower?

50. Gas Stoichiometry The ideal gas equation is very useful
For example, if we know the pressure, volume, and temperature of for a given sample of gas, we can calculate the number of moles present using the equation: PV = nRT
As it turns out, one mole of gas at STP (standard Temperature and Pressure) occupies 22.4 liters

51. Gas Stoichiometry
At STP, (273 K, 1 atm) 1 mole of an ideal gas occupies 22.4 liters
And if you recall, 1 mole of gas molecules is equal to avagadro’s number x 1023
1 mole of gas occupies
22.4 liters at STP

52. Gas Stoichiometry
The volume of 22.4 liters is called the molar volume of an ideal gas
The conditions 273 K and 1 atm if you remember is called standard temperature and pressure (STP)
The Molar volume of one mole of an ideal gas equal to 22.4 liters at STP or 1 mole
22.4 liters

53. What is the molar volume of an ideal gas?
The volume of one mole of an ideal gas equal to _____liters at STP or
22.4
Answer Bank
attract
atoms
22.4 liters
energy
Distances
temperature
pressure
_1 mol_
Conversion factor =
22.4 liters

54. Practice: A sample of nitrogen gas has a volume of 1.75 liters at STP
How many moles of N2 are present?
We need to use the conversion factor of 1 mol = 22.4 liters at STP
1.75 L N2
1.00 mol N2
= mol of N2 or 7.8 x 10-2
22.4 L N2

55. Practice:
Quicklime, CaO is produced by heating calcium carbonate CaCO3. Calculate the volume of CO2 produced at STP from the decomposition of 152 g of CaCO3 according to the reaction:
CaCO CaO + CO2
= 44.2 grams
of NH3
152 g CaCO3
1 mol CaCO3
22.4 L CO2
1 mol CO2
= 34.1 L CO2
100 g CaCO3
1 mol CaCO3
1 mol CO2

56. Kinetic Molecular Theory
A relatively simple model that attempts to explain the behavior of an ideal gas is the Kinetic Molecular Theory
This model is based upon speculations about the behavior of the particles (atoms or molecules) in a gas

57. Kinetic Molecular Theory
The assumptions of the Kinetic Molecular Theory can be stated as follows:
5. The average Kinetic energy of the gas particles
is directly proportional to the Kelvin temperature
of the gas
3. The particles are in constant random motion, colliding
with the walls of the container. These collisions with
the walls cause the pressure exerted by the gas
2. These particles are so small, compared with the
distances between them, that the volume (size)
of the individual particles can be assumed
to be negligible
1. Gases consist of tiny particles (atoms or molecules)
4. The particles are assumed
not to attract or to repel each other

58. What is the Kinetic Molecular Theory?
atoms
Gases consist of ______or molecules
These particles are small, compared to the ________between them, that the volume (size) of the individual particles can be assumed to be negligible
Gas particles are in constant random motion, colliding with walls of the container exerting a _________
The particles are assumed not to _________or to repel each other
Average Kinetic _______of the gas particles is proportional to the temperature of the gas (more heat = faster molecules)
distances
Answer Bank
attract
atoms
22.4 liters
energy
Distances
temperature
pressure
pressure
attract
energy

59. Summarize:
When given temperature, pressure, or volume of a gas, you would use the _________gas law
2. When solving for the number of moles of a gas, you would use the _________ gas law
3. When given a mixture of gases, you would use ________ gas law
4. At STP, 1 mol of an Ideal gas has a volume of ______liters
Answer Bank
ideal
combined
22.4 liters
Daltons