1. Behavior of Gases

2. Kinetic Molecular Theory (KMT)
Theory related to motion of particles.
Particles of an ideal gas…
have elastic collisions.
are in constant, random, straight-line motion.
have an avg. KE directly related to Kelvin temperature.
have no volume.
don’t attract or repel each other.

3. Real Gases But….particles in a REAL gas… Have their own volume
Although it’s really small relative to total volume of gas
Can attract each other
Weakly, usually Van Der Waals force only!!

4. When is a Gas Most Ideal? PLIGHT Thus, gas behavior is most IDEAL…
When gas particles are tiny, have weak attractive forces, are far apart and moving fast.
at low pressures
at high temperatures
when very small in size
when nonpolar
PLIGHT

5. Characteristics of Gases
Gases expand to fill any container uniformly.
Are in random motion, have no attraction
Gases have very low densities.
Particles have no volume = lots of empty space

6. Characteristics of Gases
There is a lot of “free” space in a gas.
Gases can be compressed.
no volume = lots of empty space

7. Gas Pressure
Gas pressure is a gauge of the number and force of collisions between gas particles and the walls of container
The SI unit for pressure is the pascal (Pa), but other pressure terms include atmospheres (atms), millimeters of mercury (mmHg), and torr.
Standard pressure in every unit for pressure: 
1 Atm
= kPa = 101,325 Pa
= 760 torr =760 mmHg
= 14.7lb/in2 

8. Factors Affecting Gas Pressure
Number of Moles (Amount of gas)
As # of particles increase, the number of collisions with the container wall increases.
Draw an Example:

9. Factors Affecting Gas Pressure
Volume
Smaller the volume, the greater the pressure exerted on the container.
Draw an Example:

10. Factors Affecting Gas Pressure
Temperature
As temp. increases, KE increases, this increases frequency of collisions making pressure increase.
Draw an Example:

11. Measuring Gas Pressure
Mercury Barometer
Barometer
measures atmospheric pressure
(developed by Torricelli in 1643)
Note:
The weight of the column of mercury is equal to the force of the atmospheric pressure. It the column was water the column would have to be 34 feet tall!!

13. Atmospheric Pressure
"Atmospheric Pressure" is defined as the force per unit area exerted against a surface by the weight of the air above that surface.
The pressure at point "X" increases as the weight of the air above it increases. The same can be said about decreasing pressure.
In the mountains there is less air above you so less pressure. Since gases are compressible, this creates an environment in the mountains that has less air per unit volume. It will be harder to breathe in the mountains because there is actually less O2 per volume compared to at sea level.

14. Column height measures pressure of atmosphere
Hg rises in tube until force of
Hg (down) balances the force
of atmosphere (pushing up).
(Just like a straw in soft drink)
World’s Longest Vertical Straw:
Column height measures
pressure of atmosphere
1 standard atmosphere (atm) = 760 mm Hg (or torr)
So how dense is Mercury? Watch and find out.

15. Standard Pressure (Sea Level)
101.3 kPa (kilopascal)
1 atm
760 mm Hg (also called torr)
You may be asked to convert between units of pressure!

16. Measuring Gas Pressure
U-tube Manometer
Manometer
measures contained gas pressure

18. The Gas Laws P V T
Working with Formulas

19. Gas properties can be modeled using math.
Model depends on:
V = volume of the gas (L)
T = temperature (K)
n = amount (moles)
P = pressure (atmospheres or kPa)

20. Standard Temperature & Pressure
STP
Standard Temperature & Pressure
0°C atm
273 K kPa
760 mmHg
-OR-

21. Temperature K = ºC + 273 ºC K -273 100 273 373
100
273
373
Always use absolute temperature (Kelvin) when working with gases.
K = ºC + 273

22. PV = k Boyle’s Law Pressure and volume of a gas are inversely related
at constant mass & temp
Robert Boyle ( ). Son of Earl of Cork, Ireland.
PV = k P V
Cartesian Diver:

23. Boyle’s Law
Since P x V is always a constant:
P1 x V1 = P2 x V2

24. Ex:
Consider a 3.0 L sample of gaseous SO2 at a pressure of 1.0 atm. If the pressure is changed to 1.5 atm at a constant temperature, what will be the new volume of the gas?

25. Piston Model Note: Inverse relationship.
As volume decreases, pressure increases.

26. Boyle’s Law: Mass and Temp are Constant

27. Boyle’s Law Balloon in a Vacuum Balloon: https://youtu.be/bW0j936U4EU
Pierre and Marie: Peeps in a vacuum
Cartesian Diver
Balloon in a Vacuum

28. Charles’ Law
Volume and absolute temp. (K) of a gas are directly related
at constant mass & pressure
Jacques Charles ( ). Isolated boron and studied gases. Balloonist. V T

29. Think of it this way.
As temperature of the gas increases, gas molecules begin to move around more quickly and hit the walls of container with more force, thus the volume will increase.
Keep in mind that you must use only the Kelvin temperature scale when working with temperature in all gas law formulas!

30. V1 = V2 T1 T2 Charles’ Law Since V/T is always a constant:
Can Crush

31. Ex:
A sample of gas at 15ºC and 1 atm has a volume of 2.50 L. What volume will this gas occupy at 30ºC and 1 atm?

32. Charles Law: Mass and Pressure are Constant

33. Charles’ Law Pour Liquid Nitrogen on Balloon!!
Bill Bye Vaccuum:
Can Crush:
Big Can Crush

34. Gay-Lussac’s Law
Pressure and absolute temp. (K) of a gas are directly related
at constant mass & volume P T

35. Gay – Lussac’s Law
Since P/T is always a constant:
P1 = P2
T T2

36. Ex:
Find the final pressure of gas at 150. K, if the pressure of gas is 210. kPa at 120. K if the volume remains constant

37. Review of 3 Gas Laws Summary of Changing Variables

38. Combined Gas Law (on Ref Table)
The good news is that you don’t have to remember all three gas laws!
We can combine them into a single equation. If you should only need one of the other gas laws, you can cover up the item that is constant and you will get that gas law!
P1V1 T1 =
P2V2 T2
P1V1T2 = P2V2T1

40. Example
A sample of He (g) has a volume of L, a pressure of atm and a temperature of 29°C. What is the new temperature (°C) of the gas at a volume of .090 L and a pressure of 3.20 atm?
Set up Data Table
P1 = atm V1 = .180 L T1 = 302 K
P2 = atm V2= .090 L T2 = ??