1. Gases
Objective
I will know the properties of gasses and be able to calculate the quantifiable properties of gasses
Success Criteria
I will be able to calculate each of the four quantifiable properties using the appropriate equation

2. Video Links Liquid Nitrogen and Balloon Demo Link
Charles Law Balloon Demo Link
Boyle’s Law Demo Link

3. Collecting Background
1. What are the physical properties of a gas? 2. What are the quantitative (measurable) properties of gasses?
3. What are the units of pressure? How do you convert between the units?
4. Describe the different ways that the measurable properties can be related (the laws)?

4. Characteristics What are the physical properties of a gas?
Gases are fluid
In essence, gases can flow
Gases have low density
Gases are highly compressible
Gases completely fill their container

5. Pressure
Pressure is defined as the amount of force exerted per unit area of surface
How hard the gas is pushing on the container
There are several units of pressure
Atmosphere (atm)
Kilopascal (kPa)
Millimeters of Mercury (mm Hg)
Torr (torr)
Pounds per square inch (psi)

6. Pressure Converting Units of Pressure
1.00 atm= kPa=760 torr=760 mm Hg
Practice Problems
The vapor pressure of water at 50.0oC is 12.33kPa. What is the value in atmospheres?
(12.33kPa)(1.00atm/ kPa)=0.122atm
In thermodynamics, the standard pressure is 100.0kPa. What is this value in mm Hg?
(100.0kPa)(760mm Hg/ kPa)=750.1mm Hg

7. Quantifiable Properties
There are four measurable properties of gases
P is pressure
T is temperature (must be measured in Kelvin)
K = oC + 273
V is the volume
n is the number of moles of the gas

8. STP Standard Temperature and Pressure (STP)
Standard Temperature is 0oC
Standard Pressure is 1.00atm
ΔG° = ΔH° – T ΔS°
The superscript indicates at STP

9. Boyle’s Law
Boyle’s Law discusses the relationship of pressure and volume
This shows that as the pressure increases, the volume decreases.
This is an inverse relationship
PV = k1
P = k1/V where k1 is the pressure-volume constant
And if we keep Temperature and the number of particles constant, but change
either pressure or volume we
then have:
P1V1=P2V2

10. Boyle’s Law
A sample of oxygen gas has a volume of 150.0mL at a pressure of 0.947atm. What will the volume be at a pressure of 1.000atm if the temperature remains constant?
P1V1=P2V2
(0.947atm)(150.0mL)=(1.000atm)V2
V2=142mL
Be sure your answers are in Significant Figures!

11. Boyle’s Law
A balloon has a volume of 456mL at a pressure of 761torr. It is taken under water in a submarine to a depth where the air pressure in the submarine is 3.3atm. What is volume of the balloon if the temperature remains constant?
Be sure all variables are in the same units
(761torr)(1.00atm/760torr)=1.00atm
P1V1=P2V2
(1.00atm)(456mL)=(3.3atm)V2
V2=138mL=140mL

12. Charles’ Law
Charles’ Law discusses the relationship between Temperature and Volume
This shows that as the temperature increases, the volume increases
This is a direct relationship
V/T=k2
At a constant pressure and number of particles, if either temperature
or volume change we have:
V1/T1=V2/T2

13. Charles’ Law
A sample of neon gas has a volume of 752mL at 25.0oC. What is the volume at 50.0oC if the pressure remains constant?
Change the degrees in to Kelvin
25.0oC = 298 K; 50.0oC = 323 K
V1/T1=V2/T2
(752 mL)/(298 K)=V2/(323K)
V2 = 815 mL

14. Gay-Lussac’s Law
Gay-Lussac’s Law discusses the relationship between temperature and pressure
This shows that as the temperature increases, the pressure increases.
P = k3T where k3 is the temperature-pressure constant
P/T = k3
At a constant volume and number of particles, if either the temperature or
pressure changes, we use this
equation:
P1/T1=P2/T2

15. Gay-Lussac’s Law
At 122oC, the pressure of a sample of nitrogen is 1.07atm. What will be the pressure at 205oC, assuming constant volume?
First change temperature to Kelvin
122oC = 395 K; 205oC = 478 K
P1/T1=P2/T2
(1.07 atm)/(395 K)=P2/(478 K)
P2= 1.29 atm

16. Combined Gas Law
When the three different laws just discussed are analyzed, what would they be if they are all combined?
PV = k1
V/T=k2
P/T = k3

17. Combined Gas Law PV/T = k4
If the number of moles remains constant, we can solve for any of the other variables
P1V1/T1= P2V2/T2
Also used is Standard Temperature and Pressure (STP)

18. Combined Gas Law
At a pressure of torr and 24.2oC, Xenon has a volume of 0.350L. What will the volume be at STP?
First change temperature to Kelvin
24.2oC = K
Change the pressure to atmospheres
(780.0 torr)(1.00 atm/760 torr) = 1.03 atm
P1V1/T1= P2V2/T2
(1.03atm)(0.350 L)/(297.2K) = (1.00atm)V2/(273K)
V2 = L

19. Diffusion and Effusion
Diffusion is the movement of particles from high density to low density
Popping a balloon
Effusion is the passage of gas molecules under pressure through a tiny opening
Nail in a tire

20. Graham’s Law of Diffusion
In Graham’s Law of Diffusion, we will analyze the kinetic energy of two different gases
Kinetic energy formula is 1/2mv2
m is the mass (in this case molar mass)
v is the velocity of the molecule
Graham’s Law states that the kinetic energy of the first gas will equal the kinetic energy of the second gas
m1v12= m2v22

21. Graham’s Law of Diffusion
Oxygen molecules have an average speed of 480 m/s at room temperature. At the same temperature, what is the average speed of molecules of sulfur hexafluoride?
Molar mass of Oxygen is g/mol (O2)
Molar mass of SF6 is g/mol
m1v12= m2v22
(32.00 g/mol)(480 m/s)2= ( g/mol) v2
v = 220 m/s

22. Dalton’s Law of Partial Pressures
Dalton’s law of partial pressures states that the total pressure of a mixture of gases is equal to the sum of the partial pressures of each gas
PT = P1 + P2 + P3 + ……
A 42.0 mL sample of hydrogen is collected over water at 30.0oC. What is the total pressure if the pressure of the dry gas torr and the vapor pressure of water at 30.0oC is 18.6 torr?
PT = torr torr
PT = torr

23. Essential Information
1.00 atm= kPa=760 torr=760 mm Hg
STP: 273 K and 1.00 atm
Dalton’s Law: PT = P1 + P2 + P3 + ……
Combined Gas Law: P1V1/T1= P2V2/T2
Gay-Lussac’s Law: P1/T1=P2/T2
Charles’ Law: V1/T1=V2/T2
Gramham’s Law: m1v12= m2v22
Boyle’s Law: P1V1=P2V2
Ideal Gas Law: PV=nRT where R is the gas constant