1. States of Matter: Gases

2. Characteristics of Gases
Gases expand to fill any container.
random motion, no attraction
Gases are fluids (like liquids).
no attraction
Gases have very low densities.
no volume = lots of empty space

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

4. 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.
have an avg. KE directly related to Kelvin temperature.

5. Elements that exist as gases at 250C and 1 atmosphere
5.1

6. 5.1

7. Pressure
Which shoes create the most pressure?

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

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

10. 10 miles 0.2 atm 4 miles 0.5 atm Sea level 1 atm
5.2

11. And now, we pause for this commercial message from STP
OK, so it’s really not THIS kind of STP…
STP in chemistry stands for Standard Temperature and Pressure
Standard Pressure = 1 atm (or an equivalent)
Standard Temperature = 0 deg C (273 K)
STP allows us to compare amounts of gases between different pressures and temperatures

12. Effect of intermolecular forces on the pressure exerted by a gas.
5.8

13. Standard Temperature & Pressure
STP
STP
Standard Temperature & Pressure
0°C K
1 atm kPa
-OR-

14. Temperature K = ºC + 273 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

15. Boyle’s Law
P α 1/V
This means Pressure and Volume are INVERSELY PROPORTIONAL if moles and temperature are constant (do not change). For example, P goes up as V goes down.
P1V1 = P2 V2
Robert Boyle ( ). Son of Earl of Cork, Ireland.

16. Scuba Diving and the Gas Laws
Chemistry in Action:
Scuba Diving and the Gas Laws
Depth (ft)
Pressure (atm) 1 33 2 66 3 P V
5.6

17. Charles’s Law If n and P are constant, then V α T
V and T are directly proportional.
V V2 =
T T2
If one temperature goes up, the volume goes up!
Jacques Charles ( ). Isolated boron and studied gases. Balloonist.

18. Gay-Lussac’s Law If n and V are constant, then P α T
P and T are directly proportional.
P P2 =
T T2
If one temperature goes up, the pressure goes up!
Joseph Louis Gay-Lussac ( )

19. Combined Gas Law
P1V1/T1= P2V2/T2

20. Avogadro’s Law V a number of moles (n) V = constant x n V1/n1 = V2/n2
Constant temperature
Constant pressure
V = constant x n
V1/n1 = V2/n2
5.3

21. Ideal Gas Equation 1 Boyle’s law: V a (at constant n and T) P
Charles’ law: V a T (at constant n and P)
Avogadro’s law: V a n (at constant P and T)
V a nT P
V = constant x = R nT P
R is the gas constant
PV = nRT
5.4

22. PV = nRT PV (1 atm)(22.414L) R = = nT (1 mol)(273.15 K)
The conditions 0 0C and 1 atm are called standard temperature and pressure (STP).
Experiments show that at STP, 1 mole of an ideal gas occupies L.
PV = nRT
R = PV nT =
(1 atm)(22.414L)
(1 mol)( K)
R = L • atm / (mol • K)
5.4

23. Dalton’s Law of Partial Pressures
V and T are constant P1 P2
Ptotal = P1 + P2
5.6

24. PT = PO + PH O 2KClO3 (s) 2KCl (s) + 3O2 (g) 5.6
Bottle full of oxygen gas and water vapor
2KClO3 (s) KCl (s) + 3O2 (g)
PT = PO + PH O 2
5.6

25. 5.6

26. PA = nART V PB = nBRT V XA = nA nA + nB XB = nB nA + nB PT = PA + PB
Consider a case in which two gases, A and B, are in a container of volume V.
PA =
nART V
nA is the number of moles of A
PB =
nBRT V
nB is the number of moles of B
XA = nA
nA + nB
XB = nB
nA + nB
PT = PA + PB
PA = XA PT
PB = XB PT
Pi = Xi PT
mole fraction (Xi) = ni nT
5.6

27. Pi = Xi PT PT = 1.37 atm 0.116 8.24 + 0.421 + 0.116 Xpropane =
A sample of natural gas contains 8.24 moles of CH4, moles of C2H6, and moles of C3H8. If the total pressure of the gases is 1.37 atm, what is the partial pressure of propane (C3H8)?
Pi = Xi PT
PT = 1.37 atm
0.116
Xpropane = =
Ppropane = x 1.37 atm
= atm
5.6

28. Kinetic Molecular Theory of Gases
A gas is composed of molecules that are separated from each other by distances far greater than their own dimensions. The molecules can be considered to be points; that is, they possess mass but have negligible volume.
Gas molecules are in constant motion in random directions. Collisions among molecules are perfectly elastic.
Gas molecules exert neither attractive nor repulsive forces on one another.
The average kinetic energy of the molecules is proportional to the temperature of the gas in kelvins. Any two gases at the same temperature will have the same average kinetic energy
5.7

29. Kinetic theory of gases and …
Compressibility of Gases
Boyle’s Law
P a collision rate with wall
Collision rate a number density
Number density a 1/V
P a 1/V
Charles’ Law
Collision rate a average kinetic energy of gas molecules
Average kinetic energy a T
P a T
5.7

30. Kinetic theory of gases and …
Avogadro’s Law
P a collision rate with wall
Collision rate a number density
Number density a n
P a n
Dalton’s Law of Partial Pressures
Molecules do not attract or repel one another
P exerted by one type of molecule is unaffected by the presence of another gas
Ptotal = SPi
5.7

31. C6H12O6 (s) + 6O2 (g) 6CO2 (g) + 6H2O (l)
Gas Stoichiometry
What is the volume of CO2 produced at 370 C and 1.00 atm when 5.60 g of glucose are used up in the reaction:
C6H12O6 (s) + 6O2 (g) CO2 (g) + 6H2O (l)
g C6H12O mol C6H12O mol CO V CO2
1 mol C6H12O6
180 g C6H12O6 x
6 mol CO2
1 mol C6H12O6 x
5.60 g C6H12O6
= mol CO2
0.187 mol x x K
L•atm
mol•K
1.00 atm =
nRT P
V =
= 4.76 L
5.5