1. Gas Laws

2. Properties of Gases Particles far apart Particles move freely
Indefinite shape
Indefinite volume
Easily compressed
Motion of particles is constant and random

3. Gas Pressure
Gas pressure is the result of collisions of particles with their container.
More collisions = more pressure
Less collisions = less pressure
Unit = kPa or atm

4. Units of Pressure 1 atm = 101.3 kPa =760 torr = 760 mmHg
1 atm = 101,325 Pa
1 atm = lb/in2
1 bar = 100,000 Pa = atm
atm = atmosphere

5. Amount of Gas
If you add gas, then you increase the number of particles
Increasing the number of particles increases the number of collisions
Increasing the number of collisions = increase in gas pressure
Unit = mole

6. Volume Decreasing the volume of a container increases the compression.
Increasing compression results in more collisions with the side of the container and therefore an increase in gas pressure
Unit = L

7. Temperature
If the temp. of a gas increases, then the kinetic energy of the particles increase.
Increasing KE makes the particles move faster.
Faster moving particles hit the sides of the container more and increase gas pressure.
Unit = Kelvin (K) (K = °C + 273)

8. STP Standard Temperature and Pressure Standard Temp = 273K
Standard Pressure = 1 atm (101.3kPa, 760torr, 760mmHg)

9. Gas Laws Boyle’s Law Charles’s Law Gay-Lussac’s Law Avogadro’s Law
Combined Gas Law
Ideal Gas Law
Dalton’s Law of Partial Pressures

10. Boyle’s Law
As pressure of a gas increases, the volume decreases (if the temp is constant).
Inverse relationship
P1V 1= P2V2

13. Charles’s Law
As temperature of a gas increases, the volume increases (if pressure is constant).
Direct relationship
V 1= V2
T 1 T2

15. P 1= P2 T 1 T2 Gay-Lussac’s Law
As temperature of a gas increases, the pressure increases (if volume is constant).
Direct relationship
P 1= P2
T 1 T2

16. Combined Gas Law
P1V1 = P2V2
T T2

17. Avogadro’s Law
Equal volumes of gases at the same temperature and pressure contain an equal number of particles
V 1= V2
n 1 n2

18. Dalton’s Law of Partial Pressure
The sum of the partial pressures of all the components in a gas mixture is equal to the total pressure of the gas in a mixture.
So…all the individual pressures add up to the total pressure.
Ptotal = P1 + P2 + P3 + …

20. Ideal Gas Law
An Ideal Gas does not exist, but the concept is used to model gas behavior
A Real Gas exists, has intermolecular forces and particle volume, and can change states.

21. PV = nRT Ideal Gas Law P = Pressure (kPa or atm) V = Volume (L)
n = # of particles (mol)
T = Temperature (K)
R = Ideal gas constant
8.31 (kPa∙L) or (atm∙L)
(mol∙K) (mol∙K)

22. At what temperature would 4
At what temperature would 4.0 moles of hydrogen gas in a 100 liter container exert a pressure of 1.00 atm?
Use Ideal Gas Law when you
don’t have more than one
of any variable
Ideal Gas Law PV = nRT
T = PV/nR
= (1.00atm)(100L)
(4.0mol)(.0821atm∙L/mol∙K)
= K  300K

23. Problem #1
Oxygen occupies a volume of 66L at 6.0atm. What volume will it occupy at 920kPa?

24. Problem #2
At 25°C a gas has a volume of 6.5mL. What volume will the gas have at 50.°C?

25. Problem #3
Initially you have gas at 640mmHg, 2.5L, and 22°C. What is the new temperature at 750mmHg and 5L?

26. Extensions! PV = nRT n is moles. If we know the chemical formula for
the gas we can convert moles
to mass or to particles using
Dimensional Analysis!

27. We could also use the fact that:
moles = mass or n = m
molar mass MM
Plugging this in, we have PV = mRT MM
This can be rearranged to solve for Density which is m/V
m = P∙MM or D = P∙MM
V R∙T R∙T

28. What is the density of water vapor at STP?
D = P∙MM D = (1 atm)(18.02g/mol)
R∙T (.0821atm∙L)(273K)
mol∙K
D = g/L
NOTE: STP is exact and does not count towards
Sig Figs. Constants don’t either…so actually this
problem doesn’t have a method to calculate SFs!