1. Chapter 5
GASSES

2. Gas Pressure
Gas pressure is the force exerted by a gas per unit surface area of an object.
Relate this to ice-skating, i.e. a 150 pound person whose weight is distributed on the thin blades of ice skates. (Why do you “cut” into the ice when you skate?)
Vacuum is the space created when there are no molecules to collide with one another, therefore no pressure. (Nature abhors a vacuum.)
Atmospheric pressure is the result of molecules colliding in the atmosphere. (A barometer measures atmospheric pressure.)

3. Gas pressure continued
Pressure is measured in pascals(Pa) Example: Atmospheric pressure at sea level is kiloPascals
Standard Atmosphere (atm) is the pressure required to support 760 mm of mercury in a mercury barometer at Zero degrees Celsius.
It is important to be able to relate measured gas to standards. Standard temperature and pressure (STP) is a temp. of 0 degrees Celsius and a pressure of or 760 mm Hg or 1 atm.

4. ATMOSPHERIC PRESSURE
The air on Earth exerts pressure because of gravity. There is Atmospheric pressure, as well, it is the collision of air molecules with objects around them.
As you climb up, atmospheric pressure decreases and vice versa.
Air moves from HIGH to LOW pressure. Remember nature abhors a vacuum.

5. Weather and Pressure
The pressure is high at the surface where air is slowly descending - much too slowly to feel. And, this is going on over a large area, maybe a few hundred square miles. As air descends, it warms, which inhibits the formation of clouds. This is why high pressure is generally - but not quite always - associated with good weather.
The air that descends in high pressure areas, has to get to high altitudes in some way, and that way is by rising in areas where the pressure at the surface is low.
As air rises it cools. As the air cools, the humidity in it begins to condense into tiny drops of water, or if it's cold enough, into tiny ice crystals. If there is enough water, or ice, rain or snow begin to fall. This is why low pressure is associated with bad weather.

6. Weather maps

7. Gas Pressure
Gas Pressure is the force exerted by a gas per unit surface area of the object.
Without any particles there is no pressure, thus a vacuum.

8. Ideal Gas Constant (R)= Pressure x Volume Moles x Temperature
Ideal Gas Law: PV = nRT
Ideal Gas Constant (R)= Pressure x Volume
Moles x Temperature

9. PRESSURE AND VOLUME RELATIONSHIP
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10. Boyle’s Law

11. Boyle’s Law is Pressure/Volume relationship
FORMULA
V1P1=V2P2
25 cm3 at 75 psi changes to 20 cm3 at what new pressure?
200 kpa will occupy what volume at 60 kpa (kilopascals)
As Pressure increases the volume of a gas decreases…inverse relationship

12. Boyles Law
Pressure1 x Volume1 = Pressure2 x Volume2
For a given mass of gas at a constant temperature the volume of the gas varies inversely with the pressure.
In an inverse relationship the product of the two variable quantities is constant.

13. Examples Deep sea diving: Breathing Boyle’s Law
Nitrous Oxide forms in the body when breathing high-pressured air
The Bends: is when ascending out of water and nitrogen is diffusing out of the blood. Bubbles form.
Breathing
Inhaling, the diaphragm goes downward. Lungs are an area of low pressure allowing air to come in.
Exhaling, diaphragm goes upward.High pressure in lungs, air goes out.
The Bends Web Site =

15. Charles’s Law

16. Charles Law Volume1 = Volume2 Temperature1 Temperature2
The volume of a fixed mass of gas is directly proportional to its Kelvin temperature, if the pressure is kept constant.
In a direct relationship the ratio of the two quantities that change is constant.

17. Charles’ law Calculations
200 mls. Of a gas is at 1000C. The temp changes to 1500C, find the new Volume.
100 mls. Of a gas is at 1500C and the new volume changes to 75 mls. What is the new Temperature (in Kelvin)?

18. Hot Air Balloons

19. Thermals and Migration
How Migrating Animals Take Advantage of Thermals and Updrafts Birds, butterflies and dragonflies all take advantage of rising currents to migrate. Think about the shape of the wings of a soaring eagle, crane, hummingbird, and monarch butterfly. All these animals are so light in comparison to their large wings that even gently rising air can push them up.
Cumulous clouds are tell-tale signs of thermals
A thermal is a column of rising air, caused by uneven heating of the earth

20. Thermal Bubbles
Thermals can cause hot air balloons to rise very rapidly.

21. Temperature and Volume Law
Charles’s law states
That the volume of a
Fixed mass of gas is
Directly porportional
To its Kelvin temp. if
The pressure is kept
Constant.
As temperature increases volume increases as well

22. Examples Hot air balloon: Thermals: Charles’s Law
As the heat source increases the volume of the balloon increases allowing it to become less dense and rise.
Thermals:
Charles’s Law
Hot air pockets which have increased volume when heated which decrease their density. Therefore the hot air can rise.
Thermals condense over the ocean causing cool wind to form new thermals.
Birds use them and hot air balloons don’t like them.

23. Cars and Gas Laws http://auto.howstuffworks.com/engine3.htm

24. Gay-Lussac’s Law
The pressure of a gas is directly proportional to the Kelvin temperature if the volume remains constant.
P1 / T1 = P2 / T2

25. Combined Gas Law P1 x V1 = P2 x V2 T1 T2
Pressure times Volume divided by Temperature  the new Pressure times Volume divided by Temperature

26. Boyle’s Law Problem> SOLVE!
V1 = 25 mL.
P1 = 100 kPa
P2 = 125 kPa
V2 = X (variable)
25(100) = X(125)
2500 = 125X
20 = X
Charles’ Law Problem > SOLVE!
(Convert all temps. To Kelvin)
V1 = 200 mLs
T1 = 30o C. = 303o K
V2 = X
T2 = 100o C =373o K
200/303=X/373
74600=303X
X=246mls

27. Combined gas law-
V1=150ml
P1=101.3kpa
T1=2730K
V2=300ml
P2=X
T2=3230K
(150)(101.3)/323=(300)(X)/273
X= 60 kpa

28. Daltons Law
The total pressure exerted by a mixture of gases is equal to the sum of the partial pressure of the component gases.
Ptotal = PA + PB + PC….
Problem: Find the partial pressure of Nitrogen, Oxygen, other gases in the room…use today’s barometer reading.

29. Mt. Everest Physiology on Mt. Everest 10.67 kPa of O2 needed by humans
Pressure on summit: 1/3 STP

30. gas masks
Pilots and mountaineers must have supplemental oxygen when they are working in high altitudes, where oxygen is scarce.

31. Grahams Law
The rate of effusion of a gas is inversely proportional to the square route of the gas’s molar mass. This relationship is also true for the diffusion of gasses.

32. Graham’s Law: The diffusion rate of 2 gases is inversely
Proportional to the square route of the molecular gases.
Compare gas A to gas B
Rate of diffusion Gas A = square root Gas B Mass
Gas B Gas A Mass
Smaller masses diffuse faster
To solve: Put larger mass on top, the answer = how
many times faster the smaller gas diffuses.
Example: Hydrogen diffuses 4.36 times faster
than fluorine.