1. Gases

2. Review KMT (kinetic molecular theory)

3. Molecules have vibrational motion
Molecules vibrate, rotate and translate
Molecules vibrate and rotate

4. Kinetic Molecular Theory
Gases consist of tiny particles. (atoms or molecules)
These particles are so small, compared to the distances between them, that the volume (size) of the individual particles can be assume to be negligible.(zero)
The particles are in constant motion, colliding with the walls of the container. These collisions with the wall cause the pressure exerted by the gas.
The average kinetic energy of the gas particles is directly proportional to the Kelvin temperature of the gas.

5. Properties of Real Gases
can be compressed
exert pressure on whatever surrounds them
expand into whatever volume is available
easily diffuse into one another
can be described in terms of temperature, pressure, volume and amount

6. Pressure gases exert a pressure on the walls of their container.
pressure is defined as force per unit area:

8. Atmospheric Pressure
The atmospheric pressure can be measured using a barometer.

9. Standard atmospheric pressure supports a column of mercury about 760 mm high.
760 mm Hg = 1 atm= kPa

11. Pressure Conversion
If the barometer reads mm Hg, what is the atmospheric pressure in atm and kPa?
1 atm
753.3 mm Hg
= atm
760 mm Hg
kPa
753.3 mm Hg
= kPa
760 mm Hg

12. Standard Temperature and Pressure
In order to compare two gases, we choose a standard temperature and pressure:
STP: standard temperature and pressure → 0.00 oC and kPa (1.00 atm.) → one mole of gas has a volume of 22.4 L
SATP: standard ambient temperature and pressure → 25.0 oC and KPa → one mole of gas has a volume of 24.8 L

13. Gas Laws

14. Carry out the CBL lab to determine the relationship between pressure and volume for a sample of gas.

15. Graph the following information
Pressure (KPa) Volume (L)
K (VP)
500
500.5
499.2
499.8
Is there a relationship between pressure and volume?
volume
pressure
P1V1 = K = P2V2

16. Boyle’s Law
For a given mass of gas at constant temperature, the volume of a gas varies inversely with pressure.
P1V1 = P2V2

18. Graph the following data
Temperature (K) Volume (L)
K (V/T)
0.0167
0.0168
temperature
volume
Is there a relationship between pressure and volume?
V1/T1 = K = V2/T2

20. Kelvin Scale
Lord Kelvin proposed an absolute temperature scale defined by:
T(K) = T(C)

21. Examples
Convert the following temperatures into Kelvin or celcius:
45 oC → K
207 oC → K
-48 oC → K
100 K → oC

22. Charles’ Law
Charles discovered that volume is directly proportional to its Kelvin temperature if a fixed mass remains under constant pressure.
V V2
T T2 =

23. V versus T for different gases

24. Lussac Law P1 P2 = T1 T2
The pressure of a gas is directly proportional to the Kelvin temperature, providing the volume and mass remain constant.
Joseph Louis Gay-Lussac and Jean-Baptistse Biot in their balloon on 24 August 1804

25. Combined Gas Law
P1V1 = P2V2
T T2

26. Avogadro’s Law
In 1811, Avogadro proposed that equal volumes of gases at the same temperature and pressure contain equal numbers of molecules.
It follows that the volume of a gas at constant temperature and pressure is proportional to number of moles.
V V2
n n2 =

27. The relationship between volume V and number of moles n.

28. The Ideal Gas Equation Combining the gas laws gives: PV = nRT
where R is called the Gas constant:
kPa R L
mol K = ×
8.314

29. Standard Temperature and Pressure
In order to compare two gases, we choose a standard temperature and pressure:
STP: 0°C and 1 atm
What is the volume of a mole of gas at STP?
1 mol
8.314 kPa L /mol K
× K =
kPa
= 22.4 L

30. Gas
Stoichiometry

31. Examples
If 6.45 grams of water are decomposed, how many liters of oxygen will be produced at STP?
2 H2O(g) ® 2 H2(g) + O2(g)
1 mol H2O
1 mol O2
22.4 L O2
6.45 g H2O
18.02 g H2O
2 mol H2O
1 mol O2

32. CH4(g) + 2 O2(g) ® CO2(g) + 2 H2O(g)
Examples
How many liters of CH4 at STP are required to completely react with 17.5 L of O2 ?
CH4(g) + 2 O2(g) ® CO2(g) + 2 H2O(g)
22.4 L O2
1 mol O2
1 mol CH4
22.4 L CH4
1 mol O2
1 mol CH4
22.4 L CH4
17.5 L O2
22.4 L O2
2 mol O2
1 mol CH4
= 8.75 L CH4

33. Avagadro
Equal volumes of gas, at the same temperature and pressure contain the same number of particles.
Moles are numbers of particles
You can treat reactions as if they happen liters at a time, as long as you keep the temperature and pressure the same.

34. CH4(g) + 2 O2(g) ® CO2(g) + 2 H2O(g)
Examples
How many liters of H2O at STP are produced by completely burning L of CH4 ?
CH4(g) + 2 O2(g) ® CO2(g) + 2 H2O(g)
2 mol H2O
17.5 L CH4
= 35.0 L H2O
1 mol CH4

35. Air Bag Chemistry

36. Air Bag Chemistry 2 NaN3(s) 2Na (s) + 3N2(g) Secondary reaction:
10 Na + 2 KNO3 K2O + 5 Na2O + N2(g)

37. Mg(s) + 2 HCl(aq) ® MgCl2(aq) + H2(g)
Measuring Gases
To measure the amount of gas produced in a reaction, it is often collected over water.
Reaction of magnesium with HCl:
Mg(s) + 2 HCl(aq) ® MgCl2(aq) + H2(g) O H
gas 2 P + =
= Patm