Gases and the Air We Breathe

1
Gases and the Air We Breathe

• Yes, I really have seen oxygen bars!

2
What is a gas?

• A gas is a substance in which
• The molecules are widely spaced
• Diffuse rapidly
• Molecules can move freely and rapidly through out
  the entire volume of their container
• Are evenly dispersed throughout the entire
  container
• Highly compressible

3
What is in air?

• Mostly nitrogen
• 80
• Some oxygen
• 20
• Traces of other gases
• Argon 1
• Carbon dioxide .03
• Wow! Isnt that a small amount to cause sooo much
  climate change

4
What is an ideal gas?

• A gas that obeys all of the gas laws at all
  times.
• Non-ideal gases do things like sink to the floor
  or are beginning to transition into liquids

5
How do we smell?

• The olfactory nerve at the top of our nasal
  cavity has receptors to bind to gas molecules in
  the air.
• We can smell 2000-5000 different compounds
• Our nerves are as sensitive as a blood hounds,
  just not as plentiful and the olfactory center of
  our brain is not as developed

6
Gaseous Systems

• Open Systems
• Allow gas to leave and not necessarily come back
• Closed systems
• Contain gas within a defined space
• All the better to study the nature of gasses
• Gas laws are based upon closed systems

7
Pressure/Volume Relationships

• Given a set volume that will not vary, if you put
  more gas in it the pressure will increase
• Ex Helium gas in a canister
• Given a set volume that will not vary, if you
  take gas out of it the pressure will decrease
• Ex As helium is used from the container the
  pressure falls

8
Pressure/Volume Relationships

• Given a volume that will vary, if you put more
  gas in it the volume will increase
• Ex Helium pumped into a balloon
• Given a volume that will vary, if you allow gas
  out, the volume will decrease
• Ex Letting the helium out of the balloon lets
  the balloon deflate

9
Pressure/Volume Relationships

• The relationship between pressure and volume is
  predictable
• Boyles Law
• P1V1 P2V2
• If you know any three of the above, you can
  calculate the fourth
• At sea level the pressure of gas is 1atmostphere
  or 760 mmHg
• 1 Pascal is 8 umHg

10
How is pressure related to volume?

• Think again about P1V1 P2V2
• If pressure goes up then volume must go down for
  the equation to still be true
• Therefore
• Pressure and volume are inversely related

11
How is temperature related to pressure?

• If temperature goes up pressure goes up
• Ex Heat a soda can and open it
• If temperature goes down pressure goes down
• Ex Put a soda can in the freezer for a while and
  then open it
• If properties move in the same direction when one
  of them is changed they are said to be directly
  proportional

12
What would pressure/temperature equations look
like?

• Charles Law
• P1 P2
• T1 T2

13
What if we look at temperature and pressure and
volume?

• If temperature goes up and pressure stays the
  same
• Volume had to go up
• If temperature goes up and volume stays the same
• Pressure had to go up
• All three of these are linked and if one varies,
  the others will also

14
Whats the difference between force and pressure?

• Force is the amount of pressure over a given area
• Ex. Lbs/ft2

15
What will a pressure/volume/temperature equation
look like?

• P1V1 P2V2
• T1 T2

16
What is STP?

• Standard Temperature and Pressure
• Standard Temperature
• 273oK
• Standard Pressure
• 1 atmosphere
• At STP a mole of any ideal gas will take up 22.4L

17
What if we add more stuff?

• What if we add more moles of a substance to a
  closed system
• What will happen to pressure?
• What will happen to volume?
• What will happen to temperature?
• What will this look like in math?

18
Ideal Gas Law

• PV nRT
• What the heck is R?
• If you take one mole of a gas at STP
• R will always come out the same!
• It is the ideal gas constant
• 0.082 L atm
• moles K

19
Importance of Ozone

• Very little of it where we need it
• Blocks UV light from the sun
• UV light kills living tissues
• Used to sterilize
• Chlorofluorocarbons
• Break down and release Cl
• React with O3 and break it down to O2

20
Global Warming and Greenhouse Gases

• A greenhouse gas holds energy in the earths
  atmosphere and prevents cooling
• Greenhouse gases include
• CO2
• H2O
• Fluorocarbons
• Sulfur hexafluoride
• Nitrous oxide
• Methane