1. Gas laws

2. Kinetic Molecular Theory
Particles in an ideal gas…
have no volume.
have elastic collisions.
are in constant, random, straight-line motion.
don’t attract or repel each other.

3. Real Gases Particles in a REAL gas… have their own volume
attract each other
Gas behavior is most ideal…
at low pressures
at high temperatures
in nonpolar atoms/molecules

4. Characteristics of Gases
Gases expand to fill any container.
random motion, no attraction
Gases are fluids (like liquids). They flow.
CO2 demo
no attraction
Gases have very
low densities.
Cats are Fluids:
They flow and fill the shape of their container

5. Characteristics of Gases
Gases can be compressed.
no volume = lots of empty space
Gases undergo diffusion
random motion

6. Characteristics of gases

7. K = ºC + 273 Temperature ºF ºC K -459 32 212 -273 100 273 373
Always use absolute temperature (Kelvin) when working with gases. ºF ºC K
-459 32
212
-273
100
273
373
K = ºC + 273

8. Pressure
Which shoes create the most pressure?

9. Pressure Barometer measures atmospheric pressure Aneroid Barometer
Mercury Barometer
Aneroid Barometer

10. Pressure KEY UNITS AT SEA LEVEL 101.325 kPa (kilopascal) 1 atm
760 mm Hg
760 torr
14.7 psi

11. Standard Temperature & Pressure
STP
STP
Standard Temperature & Pressure
1 atm K

12. Boyle’s Law

13. Boyle’s Law
The pressure and volume of a gas are inversely related at constant mass & temp P V
P1V1 = P2V2

14. Practice question
If a Helium tank that has an initial volume of mL and a pressure of 5 atm loses 50 mL of Helium what is its new pressure?
(5)(100) = P2 (50)
500 = P2 (50)
500/50 = 10
P2 = 10 atm

15. Charles’ Law

16. Charles’ Law
The volume and absolute temperature (K) of a gas are directly related
at constant mass & pressure V T
V1 = V2
T T2

17. Practice question
If a Helium balloon that has an intial volume of mL and a temperature of 240 K is placed in the sun where it heats to 300 K what is its new volume?
(100) = V2
(240) (300)
0.42 = V2
(300)
V2 = 125 mL

18. Gay-Lussac’s Law

19. P1 = P2 T1 T2 Gay-Lussac’s Law
The pressure and absolute temperature (K) of a gas are directly related
at constant mass & volume P T
P1 = P2
T T2

20. Practice question
If a Helium tank that has an initial pressure of 5 atm and a temperature of 240 K is placed in the sun where it heats to 300 K what is the new pressure?
(5) = P2
(240) (300)
0.021 = P2
(300)
P2 = 6.25 atm

21. Ptotal = P1 + P2 + ... Dalton’s Law
The total pressure of a mixture of gases equals the sum of the partial pressures of the individual gases.
Ptotal = P1 + P

22. Practice question
A scuba tank is filled with a mixture of atmospheric gases. Nitrogen exerts a pressure of 70 atm. Oxygen gas exerts a pressure of 22 atm. Argon exerts a pressure of 4 atm. A fourth gas exerts an unknown amount of pressure. We know the total pressure of the tank is 98 atm. What is the partial pressure of the fourth gas?
Ptotal = P1 + P2 + P3 + P4  98 = p4
98 = 96 + P4
98-96 = P4
2 = P4

23. UNIVERSAL GAS CONSTANT
Ideal Gas Law
PV=nRT
UNIVERSAL GAS CONSTANT
R= Latm/molK
R=8.315 dm3kPa/molK

24. Practice Question
How many moles of gas does it take to occupy L at a pressure of 2.3 atm and a temperature of K?
PV = nRT  (2.3)(120) = n (0.0821)(340)
276 = n(27.914)
276/(27.914) = n
n = 9.89 moles

25. Gas Stoichiometry Moles  Liters of a Gas STP - use 22.4 L/mol
Non-STP - use ideal gas law

26. Practice question
You are given 1 L of carbon monoxide at STP, how many moles of carbon monoxide do you have?
1 L x 1 mol = mol carbon monoxide
22.4 L