1. Chapter 5
Gases

2. What are some things you remember about gases and their behavior?
List, Pass,
Amass

3. Elemental States at 25oC Solid Liquid Gas He Rn Xe I Kr Br Se Ar Cl SNe F O P N C H Li Na Cs Rb K Tl Hg Au Hf Ls Ba Fr Pt Ir Os Re W Ta Po Bi Pb Be Mg Sr Ca Cd Ag Zr Y Pd Rh Ru Tc Mo Nb Ac Ra Zn Cu Ti Sc Ni Co Fe Mn Cr V In Sb Sn Ga Ge Al Gd Cm Tb Bk Sm Pu Eu Am Nd U Pm Np Ce Th Pr Pa Yb No Lu Lr Er Fm Tm Md Dy Cf Ho Es At Te As Si B
5 - 2
Solid
Liquid
Gas

4. Stuff You Already Know State Property Solid Liquid Gas Density Shape
Compressibility
Thermal
expansion
High High Low
Fixed Takes shape Expands
of lower part to fill the
of container container
Small Small Large
Very Small Moderate Small

5. More You Remember
In this state, the particles have sufficient energy to overcome all forces that attract them to each other.
Each particle is completely separated from the others.
This results in low densities and the fact that gases completely fill the container that holds them.

6. Gas Pressure Gases exhibit pressure on the containers that hold them.
Pressure = Force / Area
Units: N/m2 a.k.a. Pascal
Standard Pressures
760 mmHg = 1 atm = 760 torr = 1.01x105 Pa

7. One atm 760 mmHg 29.9 inHg vacuum
Manometer measures air pressure of a gas in a contained system.
Barometer measures ambient air pressure.
vacuum
One
atm
760 mmHg
29.9 inHg

8. Boyles Law P1V1 = P2V2 Pressure and volume are inversely proportional.
Examine the graph of the data:
Derivative!
Data!

9. Charles’ Law
V1/T1 = V2/T2
Volume and Temperature are directly proportional.
Check out data:
All gases intersect the x axis at a temperature of 0 Kelvin(-273 oC).
At temperatures lower than 0 Kelvin, gases would have a negative volume (impossible, as is negative Kelvin degrees)

10. Avogadro’s Law Guy-Lussac’s Law P1/n1 = P2/n2 P1/T1 = P2/T2
Also, at constant pressure and temperature, the volumes of gases involved in a chemical reaction are related by small whole numbers.
(ie: 2 “volumes” of hydrogen and 1 “volume” of oxygen combine to form 2 “volumes” of water…we can use volume and moles similarly when it comes to gas stoichiometry.)

11. Ideal Gas Law PV = nRT R = 0.0821 Latm/Kmol
When you hold variables constant, this equation can be manipulated into one of the others that we just talked about.
Since ideal gases don’t exist, this equation expresses the behavior a real gas approaches as pressure is lowered and temperature is increased.

12. Gas Stoichiometry At STP, the molar volume of a gas is 22.4 L / mole
Temperature = K
(0 oC)
Pressure = 1 atm
Gas stoichiometry problems can involve a gas law and/or the molar volume of a gas.

13. Demo and Thoughts CRUSH THE CAN What is inside the can?
Answer
Now
Rearrange the ideal gas law to get an equation to solve for the molar mass of a gas.
CRUSH THE CAN
What is inside the can?
Why does this happen?
Which gas law(s) does it
illustrate?

14. Section 5.5: Dalton’s Law of Partial Pressure
For a mixture of gases in a container, the total pressure exerted is the sum of the pressures that each gas would exert independently.
Ptotal= P1 + P2 + P3, etc…
Air is a mixture of gases:
Pair = PN2 + PO2 + PAr + PCO2 + PH2O

15. The law of partial pressures also works for moles.
Ptotal= (n1 + n2 +…)(RT/V)
In a mixture of ideal gases, it is the TOTAL NUMBER OF MOLES OF PARTICLES, not the identity of the substance, that determines the pressure.

16. Partial Pressure Try Me
Mixtures of helium and oxygen are used in scuba diving tanks to help prevent “the bends.”
For a particular dive, 46 liters of O2 and 12 liters of He were pumped in to a 5 liter tank. Both gases were added at 1.0 atm pressure at 25oC.
Determine the partial pressure for both gases in the scuba tank at 25oC. Then, determine the total pressure in the tank.

18. P total = P He + P O2
P total =
P total = 11.7 atm

19. Mole Fractions
Another way to determine the partial pressures of a gas.
X = n1 = P1
ntotal Ptotal
Chi,
mole
fraction

20. When Gas Is Collected Over Water
You must include the partial pressure of water in your calculations.
The vapor pressure of water is a constant value at each temperature. (you would need to look this up on a table or it would be given to you.)

21. Section 5.6: Effusion and Diffusion
Effusion occurs when a gas passes through a small opening in a barrier.
Diffusion occurs when two gases mix randomly and spontaneously.

22. More on Diffusion, Effusion, and speed of molecules
The speed of diffusion is much less than the theoretical velocity of the gas because of COLLISIONS.
The average speed of a gas that is effusing is proportional to the averages speed squared.
R = J/Kmol

23. Even more on velocity of molecules that are effusing and/or diffusing
Graham’s Law: The rates of the gases is proportional to the square root of the inverse of the molar masses of the gases.

24. Kinetic Molecular Theory
Kinetic Molecular Theory is an attempt to describe the behavior of an ideal gas
The particles are so tiny and spread out that their volume is negligible.
Particles in constant motion collisions w/ walls cause pressure.
Particles exert no intermolecular force.
Average KE is directly proportional to Kelvin temperature.

25. Can we explain each gas law using KMT?
Boyle’s Law
Gay-Lussac
Charles
Avogadro

26. www.wwnorton.com/college/ chemistry/gilbert/tutorials/ch8.htm
KMT tutorial
chemistry/gilbert/tutorials/ch8.htm

27. Maxwell-Boltzman Distribution Curves
Seen in wwnorton tutorial.
Illustrates the number of particles at a given velocity and temperature.

28. Gases are not Perfect Particles DO have mass and volume
Small attractive forces between particles ARE sometimes significant
Higher concentration of gas, more forces
Under extreme pressures or at low temperature, gases will condense to liq./sol.

29. Ideal vs Real behavior Nitrogen at Various Gas Various temp.
Deviations

30. But who would want to do that?!!
Well, Now What?
The ideal gas law has to be adjusted to reflect REAL gas behavior.
But who would want to do that?!!
I DO!!!
Johannes van der Waals
…Yes, he’s the intermolecular force guy, and its no coincidence!

31. What Johannes Did… 1 Ideal gas law 2 Adjusted for volume of gas 3
Adjusted for intermolecular forces 4
Glued Together
The Official
Equation 5

32. When should you use vanderWaals equation?
Whenever you want to know the REAL behavior of the gas, not just the ideal, limiting value.
Whenever you are working at low temperatures or high pressures
Whenever you need to employ KMT to explain the behavior of a gas …AND BE CORRECT ALL THE TIME.

33. But how do you know the values of a and b?
They are constants. You can look them up!

34. Show Me Problem
Calculate the pressure exerted by mol of nitrogen in a 1.00L container at 25.0oC using
The Ideal Gas Law
The van der Waals Equation
The Ideal Gas Law Way
PV =nRT
P(1.00) = (.500)(.0821)(298)
P = 12.2 atm
b) van der Waals Way
(Pobs+a(n/V)2)(V-nb)=nRT
(Pobs+1.39(.500/1.00)2)( (.0391))=(0.500)(0.0821)(298)
(Pobs +5.56)(.98045)=12.23
Pobs=(12.23/ )-5.56 = 6.92 atm

35. Try Me Problem
Calculate the pressure exerted by mol of argon in a 1.00L container at 23.0oC using
The Ideal Gas Law
The van der Waals Equation

36. Atmospheric Chemistry
Air is a homogeneous mixture!
The heavier gases exist in the lower atmosphere, while lighter gases are present in the upper atmosphere.
Radon gas found in basements because it is very heavy.
Oxygen is less prevalent at the tops of mountains.
Hydrogen is more prevalent as you gain altitude.
Troposphere (closest to us) is most greatly impacted by our every-day routines. Xe H2 He Kr N2 Ar
H2O O2 Ne
CO2
CH4 NO

37. Causes of Air Pollution and Acid Rain
-Generation of electricity
Coal burning plants
-Transportation
Combustion of petroleum

38. Acid Rain Effects on Buildings
Erosion of the stone
Blackened streaks on bricks

39. Why? What's it all mean? CaCO3 + H2SO4  CaSO4 + H2CO3
Limestone (calcium carbonate) reacts with acid rain (sulfuric acid):
CaCO3 + H2SO4  CaSO4 + H2CO3
H2CO3  CO2 gas + H2O
What's it all mean?
Calcium sulfate is soluble in water,
which means that the
limestone will wash away as the rain pours over it.

40. Chemistry of Acid Rain as caused by burning coal

41. Prevention of Acid Rain
At coal plants:
Injection of limestone and air into combustion chamber before products are allowed to escape.
(product becomes CaSO3, which is unusable, but non-toxic)

42. Air Pollution Effects on People
Burning eyes
Trouble breathing
Headaches
Fatigue
Photochemical smog

43. Chemistry of Air Pollution as caused by excessive traffic