AP Chemistry Unit 2

1
AP ChemistryUnit 2

• Chapter 5
• Pressure Boyles, Charles, Avogadros laws
  Ideal gas law gas stoichiometry Daltons law of
  partial pressures KMT of gases Effusion and
  diffusion real gases.

2
A gas
CB p. 2

• Uniformly fills any container.
• Mixes completely with any other gas
• Exerts pressure on its surroundings.

3
Pressure
CB p. 2

• is equal to force/unit area
• SI units Newton/meter2 1 Pascal (Pa)
• 1 standard atmosphere 1 atm
• 1 atm 760 mm Hg
• 1 atm 760 torr
• 1 atm 101.325 kPa

4
Figure 5.1a The pressure exerted by the gases
in the atmosphere can be demonstrated by boiling
water in a large metal can (a) and then turning
off the heat and sealing the can.
CB p. 2
5
CB p. 2
Figure 5.01b As the can cools, the water vapor
condenses, lowering the gas pressure inside the
can. This causes the can to crumple (b).
6
Figure 5.2 A torricellian barometer. The tube,
completely filled with mercury, is inverted in a
dish of mercury.
CB p. 2
7
Figure 5.3 A simple manometer.
CB p. 2
8
CB p. 2
9
Boyles law
CB p. 4

• Pressure ? Volume Constant (T constant)
• P1V1 P2V2 (T constant)
• V ? 1/P (T constant)
• Holds precisely only at very low pressures.

10
A gas that strictly obeys Boyles Law is called
an ideal gas.
CB p. 4
11
Boyles law
CB p. 4
12
Robert Boyle January 25, 1627
December 30, 1691

• Father of modern chemistry
• Instrumental in founding the Royal Society
• Developed key apparatus, the vacuum pump
• First to publish the details of his work,
  including unsuccessful experiments
• First use of the term "chemical analysis" is
  attributed to Boyle

13
Figure 5.4 A J-tube similar to the one used by
Boyle.
CB p. 4
14
Figure 5.5 Plotting Boyle's data from Table
5.1. (a) A plot of P versus V shows that the
volume doubles as the pressure is halved. (b) A
plot of V versus 1/P gives a straight line. The
slope of this line equals the value of the
constant k.
CB p. 4
15
Figure 5.6 A plot of PV versus P for several
gases at pressures below 1 atm.
CB p. 4
16
As pressure increases, the volume of SO2
decreases.
CB p. 4
17
Figure 5.7 A plot of PV versus P for 1 mol of
ammonia. The dashed line shows the extrapolation
of the data to zero pressure to give the "ideal"
value of PV of 22.41 L atm.
CB p. 4
18
Charles law
CB p. 6

• The volume of a gas is directly proportional to
  temperature, and extrapolates to zero at zero
  Kelvin.
• V bT (P constant)
• b a proportionality constant

19
Jacques Charles(1746-1823)

• Worked for the Bureau of Finances
• Met Ben Franklin in Paris 1779
• Self-taught physicist, began giving public
  lectures
• named a resident member of the Académie des
  Sciences 1795
• Amateur balloonist, ascending in a hydrogen
  balloon to an altitude of 10,000 ft. and
  redesigned hot air balloon.
• His work with gases resulted in the forming of
  Charles' Law in 1787

20
Figure 5.8 Plots of V versus T (ºC) for several
gases.
CB p. 6
21
Figure 5.9a. 5.8 except here the Kelvin scale is
used for temperature.
CB p. 6
22
CB p. 8
23
Avogadros law
CB p. 8

• For a gas at constant temperature and pressure,
  the volume is directly proportional to the number
  of moles of gas (at low pressures).
• V an
• a proportionality constant
• V volume of the gas
• n number of moles of gas

24
Figure 5.10 These balloons each hold 1.0L of
gas at 25ºC and 1 atm. Each balloon contains
0.041 mol of gas, or 2.5 x 1022 molecules.
CB p. 8
25
Ideal gas law
CB p. 10

• An equation of state for a gas.
• state is the condition of the gas at a given
  time.
• PV nRT

26
Ideal gas law
CB p. 10

• PV nRT
• R proportionality constant
• 0.08206 L atm ??? mol??
• P pressure in atm
• V volume in liters
• n moles
• T temperature in Kelvins
• Holds closely at P lt 1 atm

27
Standard Temperature and Pressure
CB p. 10

• STP
• P 1 atmosphere
• T ??C
• The molar volume of an ideal gas is 22.42 liters
  at STP

28
CB p. 10
29
CB p. 10
30
Figure 5.11 22.4 L of a gas would just fit into
this box.
CB p. 10
31
Daltons law of partial pressures
CB p. 12

• For a mixture of gases in a container,
• PTotal P1 P2 P3 . . .

32
Figure 5.12 The partial pressure of each gas in
a mixture of gases in a container depends on the
number of moles of that gas.
CB p. 12
33
CB p. 12
34
Figure 5.13 The production of oxygen by thermal
decomposition of KCIO3. The MnO2 is mixed with
the KClO3 to make the reaction faster.
CB p. 12
35
CB p. 14
36
CB p. 14
37
CB p. 14
38
(No Transcript)
39
CB p. 14
40
(No Transcript)
41
Kinetic Molecular Theory (KMT) of gases
CB p. 16

• 1. Volume of individual particles is ? zero.
• 2. Collisions of particles with container
  walls cause pressure exerted by gas.
• 3. Particles exert no forces on each other.
• 4. Average kinetic energy ? Kelvin temperature
  of a gas.

42
The meaning of temperature
CB p. 16

• Kelvin temperature is an index of the random
  motions of gas particles (higher T means greater
  motion.)

43
Figure 5.21 A plot of the relative number of
N2 molecules that have a given velocity at
three temperatures.
CB p. 16
44
CB p. 16
45
Root-mean-square-velocity
CB p. 18

• The symbol means the average of the squares
  of the particle velocities.
• The square root of is called the root mean
  square velocity and is symbolized by u rms.

46
CB p. 18
47
Diffusion vs. Effusion
CB p. 20

• Diffusion describes the mixing of gases. The
  rate of diffusion is the rate of gas mixing.

• Effusion describes the passage of gas into an
  evacuated chamber.

48
CB p. 20
49
Figure 5.22 The effusion of a gas into an
evacuated chamber.
CB p. 20
50
Figure 5.23 Relative molecular speed
distribution of H2 and UF6.
CB p. 20
51
Figure 5.24 (top) When HCl(g) and NH3(g) meet
in the tube, a white ring of NH4Cl(s) forms.
(bottom) A demonstration of the relative
diffusion rates of NH3 and HCl molecules through
air.
CB p. 20
52
Real gases
CB p. 22

• Must correct ideal gas behavior when at high
  pressure (smaller volume) and low temperature
  (attractive forces become important).

53
Real gases
CB p. 22
?
?
corrected pressure
corrected volume
Pideal
Videal
54
CB p. 22