AP Chemistry Power Point

1. CHAPTER 5 ZUMDAHL
GASES

2. 5.1 PRESSURE
• A gas uniformly fills a container and mixes
completely with any other gas
• Pressure is one of a gases most obvious properties
• See collapsing can experiment
• A device to measure atmospheric pressure is a
barometer invented in 1642 by Evangelista Torricelli
made by inverting a column of Mercury. The units
of mmHg is sometimes called Torr in honor of
Torricelli

3. TORRICELLIAN BAROMETER

4. UNITS OF PRESSURE
• A manometer is
commonly used to
measure pressure
based upon the
height of mercury it
can support.
• 1atmosphere =
760mmHg = 760 torr =
101.3kPa
• A pascal (Pa) is a
N/m2

5. 5.2 THE GAS LAWS
• Boyles Law – Robert Boyle showed that PV=k. In other
words there is an inverse relationship between pressure
and volume
• Charles Law – Jacques Charles was the first person to fill
a balloon with Hydrogen gas and make a solo flight. He
found that volume is directly proportional to
temperature. V = bT. Also if V and T are ploted on the
Kelvin scale they all go back to the same temperature
for volume. That temperature is absolute zero 0K =
-273o
C
• Avogadro’s Law. He showed that equal volumes of gas
at the same temperature and pressure contain equal
numbers of particle. V = an

6. BOYLES LAW

7. CHARLES LAW

8. AVOGADRO’S LAW
• Each of these
balloons contains 1L
of gas at 25oC and
1atm pressure.

9. 5.3 THE IDEAL GAS LAW
• The three gas laws can be combined when all the
proportionality constants are combined into one
constant R (the universal gas constant)
• The resulting equation is PV = nRT and is known as
the ideal gas law
• Where pressure is in atm and volume in L then the
gas constant R = 0.08206 L atm/K mol

10. 5.4 GAS STOICHIOMETRY
• The volume 1 mole
of an ideal gas will
occupy at STP is
22.4L

11. GAS DENSITY AND MOLAR MASS
• One very important use of the ideal gas law in in the
calculation of molar mass of a gas from its
measured density.
• Molar mass = dRT/P

12. 5.5 DALTONS LAWS OF PARTIAL
PRESSURES
• Pressure is directly
affected by the
number of moles of
gas.
• The total pressure is
the sum of each of
the partial pressures
• PT = P1+P2 ……

13. MOLE FRACTION (Χ)
• The ratio of the number of moles in a given
component in a mixture to the total number of
moles in the mixture.
• So χ1= n1/ntotal = P1/Ptotal
• This can be rearranged to give
P1 = χ1 x Ptotal

14. COLLECTING A GAS OVER WATER
• Collecting over
water involves a
mixture of the
product gas and
water vapor. The
amount of water is
called the vapor
pressure of water

15. 5.6 KINETIC MOLECULAR THEORY
1. The particles are so small compared with the distances
between them that the volume of individual particles is
assumed to be negligible (zero)
2. The particles are in constant motion. The collisions with the
walls of the container are the cause of the pressure
3. The particles are assumed to exert no forces on each other.
They are assumed neither to attract nor to repel each other.
4. The average kinetic energy of a collection of gas particles is
assumed to be directly proportional to the Kelvin
temperture of the gas

16. PATH OF A GAS PARTICLE

17. KINETIC ENERGY AND TEMPERATURE

18. THE DISTRIBUTION OF VELOCITIES

19. 5.7 EFFUSION AND DIFFUSION
• Diffusion describes the mixing of gases. A smell
spreads throughout the room as a result of the
movement of the gas particles spreading a far
apart as they can from areas of high concentration
to areas of low concentration.
• Effusion describes the passage of a gas through a
tiny orifice into an evacuated chamber. The rate of
effusion measures the speed at which the gas is
transferred into the chamber

20. GRAHAMS LAW OF EFFUSION

21. DIFFUSION

22. 5.8 REAL GASES
At different Pressures At different Temperatures

23. INTERACTIONS
• At high temperature
collisions more
elastic.
• At low
concentration
fewer interactions

24. VAN DER WAALS EQUATION

25. VAN DER WAALS CONSTANTS

26. 5.10 CHEMISTRY OF THE ATMOSPHERE
• Make up of gases in the air
• Air pollution
• Photochemical smog
• The effect of acid rain
• Use of scrubbers to remove sulfur dioxide.