1

Notes on Gases:Notes on Gases:A Summary of Chapters 13 & 14A Summary of Chapters 13 & 14

Section 1: Properties of Gases

Section 2: Gas Laws

Section 3: Gas Stoichiometry

2

Gas PropertiesGas PropertiesKinetic Molecular Theory:

1) Gases consist of large numbers of particles that are far apart.

2) When particles collide, they do not lose energy.

3) Gas particles are in continuous, rapid, random motion.

4) There are no forces of attraction between gas particles.

5) Average temperature of a gas depends on the temperature.

3

More Properties…More Properties…Expansion:

-No definite shape or volume.Gases naturally expand to fill their

containers.

Fluidity: Gas particles glide past one another causing them to “flow” like liquids.(Liquids and gases are FLUIDS.)

4

More Properties…More Properties…Low Density:

Particles are so far apart compared to solids and liquids the density is really

low…therefore, gases float!

Compressibility: Gas particles can be squeezes closer

together (causing the volume to decrease and the pressure to increase).

5

More Properties…More Properties…

Diffusion:

Natural mixing of gas particles caused by random motion.

Effusion: Process of gas particles passing

through a tiny opening. Ex. – Hole in a bike tire.

6

7

What is Pressure?What is Pressure?Pressure (P) is the force applied over a surface area. Measured in newtons (N).

P = force area

Barometers are used to measure atmospheric pressure. Measured in…

1. Millimeters of mercury (mm Hg)2. Atmospheres (atm)3. Torricelli (torr) *invented the barometer*

4. Pascal (Pa) or kilopascal (kPa)

8

Units for PressureUnits for Pressure(All calculations must be in atm!!!)

Atmospheric pressure at sea level:

1 atm = 760 mm Hg= 760 torr= 101.3 kPa

Units for TemperatureUnits for Temperature(All calculations must be in Kelvin!!!)

Converting from Kelvin CelsiusC = K – 273

Converting from Celsius KelvinK = C + 273

9

Standard Standard Temperature and PressureTemperature and Pressure

Oftentimes, chemists want to use the same conditions for several experiments…so a standard temperature and pressure was

agreed upon.

STP = 0STP = 0ºC and 1 atmºC and 1 atm

10

The Gas LawsThe Gas Laws

1. Boyle’s Law (Pressure-Volume)2. Charles’s Law (Temperature-Volume)3. Gay-Lussac’s Law (Temperature-Pressure)4. Combined Gas Law (P-T-V)5. Ideal Gas Law (P-T-V-Moles)

11

Boyle’s Law (Pressure-Volume)Boyle’s Law (Pressure-Volume)

P1V1 = P2V2

If pressure increases, volume will ________.

If pressure decreases, volume will ________.

This relationship is ________.

12

Boyle’s Law (Pressure-Volume)Boyle’s Law (Pressure-Volume)P1V1 = P2V2

If pressure increases, volume will decrease.

If pressure decreases, volume will increase.

This relationship is inverse.

Lungs Video

Marshmallows Video

13

Charles’s Law Charles’s Law (Temperature-Volume)(Temperature-Volume)

V1 = V2

T1 T2

If temperature increases, volume will _______.

If temperature decreases, volume will _______.

This relationship is ________.

14

Charles’s Law Charles’s Law (Temperature-Volume)(Temperature-Volume)

V1 = V2

T1 T2

If temperature increases, volume will increase.

If temperature decreases, volume will decrease.

This relationship is direct.

Liquid Nitrogen + Balloon55-Gallon Can

15

Gay-Lussac’s Law Gay-Lussac’s Law (Temperature-Pressure)(Temperature-Pressure)

P1 = P2

T1 T2

If temperature increases, pressure will ______.

If temperature decreases, pressure will ______.

This relationship is ________.

16

Gay-Lussac’s Law Gay-Lussac’s Law (Temperature-Pressure)(Temperature-Pressure)

P1 = P2

T1 T2

If temperature increases, pressure will increase.

If temperature decreases, pressure will decrease.

This relationship is direct.FountainEgg + Bottle

17

Wouldn’t it be easier if we only had one formula?Wouldn’t it be easier if we only had one formula?

COMBINED GAS LAW

P1 V1 = P2 V2

T1 T2

If one of these variables is constant, block it out and If one of these variables is constant, block it out and use the equation that is left.use the equation that is left.

If temperature is constant (no T) = Boyle’s LawIf temperature is constant (no T) = Boyle’s Law

If pressure is constant (no P) = Charles’s LawIf pressure is constant (no P) = Charles’s Law

If volume is constant (no V) = Gay-Lussac’s LawIf volume is constant (no V) = Gay-Lussac’s Law

18

Summary of FormulasSummary of FormulasBoyle’s Law : P1V1 = P2V2

Charles’s Law : V1 = V2

T1 T2

Gay-Lussac’s Law : P1 = P2

T1 T2

Combined Gas Law : P1 V1 = P2 V2

T1 T2

19

PRACTICE – 1 of 4PRACTICE – 1 of 4

COMBINED GAS LAW

P1 V1 = P2 V2

T1 T2

Q1: A sample of Neon gas occupies a volume of 752mL at 25ºC. What volume will the

gas occupy at 50ºC if the pressure remains constant? What law will we use?

20

PRACTICE – 2 of 4PRACTICE – 2 of 4

COMBINED GAS LAW

P1 V1 = P2 V2

T1 T2

Q2: A sample of oxygen gas has a volume of 150.mL when its pressure is 0.947atm. What will the volume of the gas be if the pressure

increases to 0.987atm? (Temperature remains constant.) What law will we use?

21

PRACTICE – 3 of 4PRACTICE – 3 of 4

COMBINED GAS LAWP1 V1 = P2 V2

T1 T2

Q3: The gas in an aerosol can is at a pressure of 3.00atm at 25ºC. Directions on the can warn the

user not to keep the can in a place when the temperature exceeds 52ºC. What would the

pressure in the can be at 52ºC? (Assume volume remains constant.) What law will we use?

22

PRACTICE – 4 of 4PRACTICE – 4 of 4

COMBINED GAS LAW

P1 V1 = P2 V2

T1 T2

Q4: A helium-filled balloon has a volume of 50.0L at 25ºC and 1.03atm. What volume will it have at 0.855atm and 10ºC? What

law will we use?

23

The Ideal Gas LawThe Ideal Gas Law

A law relates pressure, volume, A law relates pressure, volume, temperature, and the number of temperature, and the number of

moles of a gas.moles of a gas.PV = nRTPV = nRT

P = pressure (in atm)P = pressure (in atm)

V = volume (in L)V = volume (in L)

n = number of moles (in moles)n = number of moles (in moles)

R = Ideal Gas Constant (R = Ideal Gas Constant (0.0821 always0.0821 always))

T = temperature (in Kelvin)T = temperature (in Kelvin)

24

PRACTICE – 1 of 3PRACTICE – 1 of 3

Ideal Gas Law

PV = nRT

Q1: What is the pressure (in atm) exerted by a 0.500 mol sample of nitrogen gas in a

10.0L container at 298K?

25

PRACTICE – 2 of 3PRACTICE – 2 of 3

Ideal Gas Law

PV = nRT

Q2: What is the volume (in liters) of 0.250 moles of oxygen gas at 20.0ºC and 0.974

atm of pressure?

26

PRACTICE – 3 of 3PRACTICE – 3 of 3

Ideal Gas Law

PV = nRT

Q3: How many moles of chlorine (Cl2) is contained in a 10.0L tank at 27ºC and

3.50atm of pressure?

27

Final Summary of FormulasFinal Summary of Formulas

Boyle’s Law : P1V1 = P2V2

Charles’s Law : V1 = V2

T1 T2

Gay-Lussac’s Law : P1 = P2

T1 T2

Combined Gas Law : P1 V1 = P2 V2

T1 T2

Ideal Gas Law : PV = nRT

28

FINAL SECTION: Gas StoichiometryFINAL SECTION: Gas Stoichiometry

Same rules as Reaction Stoichiometry…

We are simply adding one value –

standard molar volumestandard molar volume..The volume occupied by one mole of gas at STP

(Standard Temperature and Pressure).

standard molar volume = 22.4 L/mol22.4 L/mol of gas.

29

PRACTICE – 1 of 4PRACTICE – 1 of 4

Gas Stoichiometry

Q1: A chemical reaction produces 0.0680 mol of oxygen gas. What volume (in liters) is

occupied by the gas at STP? (Remember the value 22.4L/mol.)

30

PRACTICE – 2 of 4PRACTICE – 2 of 4

Gas Stoichiometry

Q2: A chemical reaction produced 98.0 mL of sulfur dioxide gas (SO2) at STP. What was

the mass in grams of the gas produced? (Remember the value 22.4L/mol.)

31

PRACTICE – 3 of 4PRACTICE – 3 of 4

Gas StoichiometryCaCO3 CaO + CO2

Q3: How many grams of calcium carbonate must be decomposed to produce 5.00L of

carbon dioxide gas at STP? (Use PV=nRT)

32

PRACTICE – 4 of 4PRACTICE – 4 of 4

Gas StoichiometryWO3 (s) + 3H2 (g) W(s) + H2O(l)

Q4: How many liters of hydrogen gas at 35ºC and 0.980 atm are needed to react

completely with 875 g of tungsten oxide? (PV=nRT)

33

YouTube Videos – GAS HELPYouTube Videos – GAS HELP

1. Gas Stoichiometry #12. Gas Stoichiometry #23. Molar Volume Explanation4. How to Collect a Gas Experimentally5. Ideal Gas Law Example6. Diffusion of Gas Demos7. Effusion of Heavy Gas (Sulfur hexafluoride)8. Effusion of Light Gas (Hydrogen)9. Kinetic Molecular Theory of Gases10. Properties of Gases

34

Review Topics for the TestReview Topics for the Test

I. Properties of Gasesa) Kinetic Molecular Theory (5 parts)b) Fluidity, Expansionc) Compressibility, Density d) Effusion/Diffusione) Units for Temperature and Pressure f) STP

35

Review Topics for the TestReview Topics for the Test

II. Gas Laws Boyle’s Law : P1V1 = P2V2

Charles’s Law : V1 = V2

T1 T2

Gay-Lussac’s Law : P1 = P2

T1 T2

Combined Gas Law : P1 V1 = P2 V2

T1 T2

Ideal Gas Law : PV = nRT

36

Review Topics for the TestReview Topics for the Test

III. Gas Stoichiometry • Converting from moles Liters

• Converting from Liters moles

• Converting from grams Liters

• Converting from Liters grams

• Using a balanced equation to predict grams or Liters by using PV=nRT

37

Remember: - Scientific Calculator- Pencil- Scratch paper- 3x5 Note Card (front/back)