Chapter 13
13.1 Pressure- force exerted over an area
(pressure = force x area) (F in Newtons, area in m2)
(1 N-m2 = 1 Pascal = 1 Pa)
Barometer- device for measuring atmospheric pressure (Torricelli)
Manometer- device for measuring pressure in a container
Units of Pressure
1 atm = 760.0 mm Hg = 760.0 torr = 101, 325 Pa = 101.3 kPa
Example: 525 mm Hg x 1 atm/ 760 mm Hg = 0.691 atm
Problem: convert 105.2 kPa to atm
Problem: Convert 225,400 Pa to mm Hg
Figure 13.2:
A glass tube is filled
with mercury and
inverted in a dish of
mercury at sea level.
Figure 13.3: Gas pressure =
atmospheric pressure – h.
Figure 13.3: Gas pressure =
atmospheric pressure + h.
13.2 Pressure & Volume: Boyle’s Law
Pressure
Volume Temperature
# of Particles of Gas
If temperature and the # of particles of Gas are held constant, then
pressure and volume are indirectly proportional.
PxV = k
P1V1 = P2V2
Graph
Example:A sample of neon to be used in a neon sign has a volume of
1.51 L at a pressure of 635 torr. Calculate the volume of the gas after it
is pumped into the glass tubes of the sign, where it shows a pressure of
785 torr.
V2 = (V1 x P1)/P2 = (1.51 L x 635 torr)/785 torr = 1.22 L
Problem: V = 53.2 mL @ 785 mm Hg; V = ? @ 700 mm Hg
V2 = (V1 x P1)/P2 = (53.2 mL x 785 mm Hg)/700 mm Hg = 59.7
mL
Table 13.1
Figure 13.4:
A J-tube similar
to the one used by
Boyle.
Figure 13.5: A plot of P versus V from
Boyle’s data.
Figure 13.6: Illustration of Boyle’s
law.
13.3 Volume & Temperature : Charles’s Law
Pressure
Volume
Temperature # of Particles of Gas
If pressure and # of particles of gas are held constant, then temperature
and volume are directly proportional. (Note: Temperature MUST be in
Kelvin)
V/T = k
V1/T1 = V2/T2
Graph
Example: 13.3, p. 406
V2 = (V1 x T2)/T1 = (23 cm3 x 291 K)/301 K = 22 cm3
Problem: If a 45.0 mL sample of gas at 26.5oC is heated to 55.2oC,
what is the new volume of the gas sample at constant pressure?
V2 = (V1 x T2)/T1 = (45.0 mL x 328.2K)/299.5 K = 49.3 mL
Figure 13.7: Plots of V (L) versus T
(°C) for several gases.
Figure 13.8: Plots of V versus T using
the Kelvin scale for temperature.
13.4 Volume & Moles: Avogadro’s Law
Pressure
Volume
Temperature # of Particles of Gas
If pressure and temperature are held constant, then volume and # of
particles of gas are directly proportional.
V/n = k
V1/n1 = V2/n2
Example:Consider two samples of nitrogen gas (composed of N2
molecules). Sample 1 contains 1.5 mol of N2 and has a volume of
36.7 L @ 25oC and 1 atm. Sample 2 has a volume of 16.5 L at 25oC
and 1 atm. Calculate the # of moles of N2 in sample 2.
n2 = (n1 x V2)/V1 = (1.5 mol x 16.5 L)/36.7 L = 0.67 mol
Problem: If 0.214 mol of argon gas occupies a volume of 652 mL at
a particular temperature and pressure, what volume would 0.375 mol
of argon occupy under the same conditions?
V2 = 1.14 L
Figure 13.9: The relationship
between volume V and number
of moles n.
13.5 Ideal Gas Law
Pressure
Volume
Temperature # of particles of gas
R- universal gas constant
R = (1.000 atm)(22.4 liters) =
(1 mol)(273K)
PV = nRT
Example:
Problem:
Combined Gas Law- if # of particles of gas is held constant, then
the other quantities vary in this relationship:
P1V1/T1 = P2V2/T2
Example:
Problem:
13.6 Dalton’s Law of Partial Pressures
Partial pressure- the pressure that a gas would have if it was alone in a
container
Total pressure exerted is the sum of the partial pressures.
PT = p1 + p2 + … + pn
Example:
Problem:
Figure 13.10: When two gases are
present, the total pressure is
the sum of the partial pressures
of the gases.
Figure 13.11: The total pressure of a
mixture of gases depends on
the number of moles of gas
particles present.
Figure 13.12: The production of
oxygen by thermal decomposition.
Postulates of KMT.
Figure 13.13: (a) A gas confined in a cylinder
with a movable piston. (b) The temperature of
the gas is increased at constant pressure P ext.
Figure 13.14: A gas sample is
compressed.
13.9 The Implications of the Kinetic Molecular Theory
The average kinetic energy of gas particles is directly proportional to
the Kelvin temperature. (I.e., the warmer the gas, the faster the
particles move)
13.10 Real Gases Gas Laws do not work accurately when
temperature is low and pressure is high. (Gas  liquid)
13.11 Gas Stoichiometry
1 mole of any gas occupies 22.4 liters of volume at 0oC and 1 atm
0oC and 1 atm are called Standard temperature and Pressure (STP)
(22.4 liters is called molar volume)
Example:
Problem:
(not in textbook)
Graham’s Law- compares the rate of effusion (movement of a gas
through a pinhole) of one gas to the rate of effusion of another gas;
they are indirectly proportional to the square root of the their
respective molar masses.
Rate gas 1
= (molar mass gas 2)1/2
Rate gas 2
(molar mass gas 1)1/2