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Chapter 11
("down and dirty or condensed soup version"))
Gases
Unpolluted air at sea level
78% N2
21% O2
1% Argon
trace CO2 and H20
The air we breathe is composed of the above mixture!!!
Nature of Gases
1. Gases fill a container completely.
2. Gases are compressible.
3. Gases have a low density D=Mass
Volume
Gas
1g/L
Liquid 2g/mL
4. Gases exert a uniform pressure on all inner surfaces of a container because they
completely fill the container.
Pressure What is it?
Pressure is the force exerted on a unit area.
Pressure exerted by the atmosphere or the earth is called atmospheric pressure.
Units of Pressure
1 atm = 760 mmHg = 760 torr = 1.01325 x 105 Pascal
Pascal is the SI unit for pressure.
1 atm = 14.96 psi (pounds per square inch)
*example 11.1 pg 365
Barometer measures atmospheric pressure
Manometer measures pressure of an enclosed gas.
Kinetic molecular theory of Gases (Briefly explains Ideal Gas behavior)
1. Gas consists of tiny, non-interacting particles that are very far apart
2. Gas particles are in constant random motion
3. When gas particles collide with the walls of a container pressure is produced
4. Average Kinetic energy of these particles is proportional to the Kelvin
temperature.
Boyle’s Law
P1 V1 = P2 V2
(n and T are constant)
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Boyles law continued.
The volume of a fixed amount of gas at a given temperature is inversely proportional to
the applied pressure.
*Example 11.2 pg 369
Charles Law
V1 = V2
T1
T2
(n and P are constant)
The volume of a fixed amount of gas is directly proportional to its Kelvin temperature
as long as the pressure is kept constant. If temperature is given in Celsius you must
convert to Kelvin before you start the problem.
*Example 11.3 pg 374
Combined Gas Law
P1V1
T1
(n is constant )
n= number of moles
= P2V2
T2
Example 11.4 pg 376
Avogadro’s law
Equal volumes of any two gases at the same temperature and pressure contain equal
moles of molecules.
Standard Temperature and Pressure or STP is defined as 0o C and 273 K and a
pressure of 1 atm or 760mmHg
At STP ,the volume of 1 mole of any gas has been shown by experiment to be 22.4 L.
32 grams of O2 = 1 mole = 22.4 L
2 grams of H2 = 1 mole = 22.4 L
1 mole = 6.022 x 1023 molecules = 22.4 L
molar volume of a gas is 22.4 L
molar mass of 22. 4 L is the molecular wt in grams of 1 mole = H2 =2grams
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Ideal Gas Law
PV=nRT
R = molar gas constant 0.08206 L . atm/(K . mol)
n = moles
P = pressure (atm)
V = volume (L)
T = temperature in Kelvin
will always be given in this class
*Example 11.6 pg 381
Mixture of Gases
Dalton’s law of partial pressure
The sum of the partial pressures of each of the components in a gas mixture must equal
the total pressure.
Ptotal = PN2 + PO2 +PAR
Ptotal = 0.78 atm + 0.21atm + 0.01atm
= 1.0 atm
*Example 11.9 pg 386