1. Gases
Dr. Ron Rusay
Summer 2004
© Copyright 2004 R.J. Rusay

2. Gases

3. Gases: Pressure, Mass, Volume, Temperature

4. Pressure Pressure is equal to force/unit area
SI units = Newton/meter2 = 1 Pascal (Pa)
1 standard atmosphere = 101,325 Pa
1 standard atmosphere = 1 atm =
29.92 inches of Hg
34 feet of H2O

5. Measuring Atmospheric Pressure Toricellian Barometer
1 standard atmosphere
1 atm = mm Hg
29.92 inches of Hg
34 feet of H2O

6. Pressure & Volume Boyle’s Law*

7. Changing Volume
@ constant temperature
P 
V 
P 
V ?

8. Pressure & Volume Boyle’s Law*

9. Boyle’s Law ** Pressure  Volume = Constant (T = constant)
V  1/P (T = constant)
(*Holds precisely only at very low pressures.)

10. Changing Volume **

11. Pressure vs. Volume

12. Ideal Gases
Real vs. “Ideal”
Definition: A gas that strictly obeys Boyle’s Law is called an ideal gas.

13. Temperature & Volume (@ constant pressure)

14. Temperature & Volume
77 K = ? oC

15. Temperature & Volume
What happened in the balloon on a molecular level?

16. Charles’s Law **
The volume of a gas is directly proportional to temperature, and extrapolates to zero at zero Kelvin.
V = T (P = constant)
= a proportionality constant

17. Temperature and Volume (@ constant P)

18. Pressure vs. Temperature (@ constant V)

19. Pressure vs. Temperature (@ constant V)
“Gay Lussac’s Law”

20. Vapor Pressure vs. Temperature solid  liquid  gas

21. Pressure, Volume & Temperature
(PV&T)

22. Molecular Motion / Theory
The Meaning of Temperature
Temperature (Kelvin) is an index of the random motions of gas particles (higher T means greater motion.)

24. Standard Temperature and Pressure
“STP”
P =
T =

25. Avogadro’s Law
For a gas at constant temperature and pressure, the volume is directly proportional to the number of moles of gas (at low pressures).
V = n
= proportionality constant
V = volume of the gas
n = number of moles of gas

26. Volume vs. n (moles of a gas)

27. Ideal Gas Law ** An equation of state for a gas.
“state” is the condition of the gas at a given time.

28. Ideal Gas Law ** PV = nRT Holds closely at P < 1 atm
R = proportionality constant
= L atm  mol
P =
V =
n =
T =
Holds closely at P < 1 atm

29. Molar Volume at Standard Temperature and Pressure
“STP”
P = 1 atmosphere
T = C
The molar volume of an ideal gas is _____ liters at STP

30. Dalton’s Law of Partial Pressures **
For a mixture of gases in a container, (P constant V &T)
PTotal = P1 + P2 + P