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. Drill #1 3/34 & 25/2014 What is the density of water vapor at STP?
Standard Temperature and Pressure
Standard Temp = 273K
Standard Pressure = 1 atm (101.3kPa, 760torr, 760mmHg)
One mole of an ideal gas will occupy a volume of 22.4 liters at STP
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!

9. Answer
D = g/L

10. Drill – pd 4A 4/23/15
What volume would be occupied by grams of hydrogen gas at a pressure of 2.01 atmospheres and a temperature of 35.0°C?

11. Answer
4.09 L H2

12. Standard Temperature and Pressure
STP
Standard Temperature and Pressure
Standard Temp = 273K
Standard Pressure = 1 atm (101.3kPa, 760torr, 760mmHg)
One mole of an ideal gas will occupy a volume of 22.4 liters at STP

13. Gas Laws Dalton’s Law of Partial Pressures Boyle’s Law Charles’s Law
Gay-Lussac’s Law – already have used
Avogadro’s Law
Combined Gas Law
Ideal Gas Law
Graham’s Law – last one to learn

14. 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

15. Graham’s Law

16. Diffusion and Effusion
Diffusion – the gradual mixing of 2 or more gases due to their spontaneous, random motion
Effusion – molecules of gas confined in a container randomly pass through a tiny opening in the container

17. The rates of diffusion and effusion depend on the velocities of the gas molecules.
Velocity is determined by the equation
KE = ½mv2

18. Kinetic energy is dependent on temperature, meaning two different gases will have the same kinetic energy at the same temperature
½m1v12 = ½m2v22

19. Graham’s Law of Diffusion:
Rates of diffusion of gases at the same temp and pressure are inversely proportional to the square roots of their molar masses.

20. Compare the rates of diffusion of hydrogen and oxygen at the same temperature and pressure.
rateH2 √MO √32.00g/mol
rateO2 √MH √2.02g/mol
Hydrogen diffuses 3.98 times faster than oxygen
3.98

21. Drill – pd 3 4/23/15
Compare the rate of effusion of carbon dioxide with that of hydrogen chloride at the same temperature and pressure.

22. Practice Prob. #1 Answer
Carbon dioxide will effuse about 0.9 times as fast as hydrogen chloride.

23. Practice Problem #2
A sample of hydrogen effuses through a porous container about 9 times faster than an unknown gas. Estimate the molar mass of the unknown gas.

24. Practice Prob. #2 Answer
160 g/mol

25. Homework
Mixed Practice Problems

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

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

31. 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

32. Combined Gas Law
P1V1 = P2V2
T T2

33. 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

34. 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 + …

36. 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.

37. 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)

38. 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

39. If we know the chemical formula for the gas we can convert moles
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!

40. 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