Gas laws describe the behavior of gases and can be used to interconvert pressure, volume, temperature, and amount of gas. The three main gas laws are: [1] Boyle's law relates pressure and volume at constant temperature; [2] Charles' law relates volume and temperature at constant pressure; and [3] Gay-Lussac's law relates pressure and temperature at constant volume. Together these laws form the combined gas law. Standard temperature and pressure provide reference points for gas measurements and calculations.

1. Gas Laws
QBA Miguel Ängel Castro Ramirez

2. Pressure: Peer, gas, blood, teen...

3. Measuring pressure
• Force per unit area • Units in use by
• Force is measured in chemists include
Newtons • Pascals (Pa) or KPa
(Kg*m/sec2) • Millimeters of
• Area can be mercury (mmHg)
measured in meters • Atmospheres (atm)
• Non-SI units were • Torrs (torr – no
PSI, or pounds per abbreviation)
square inch

4. Converting
• 1 atmosphere = 760 mmHg
• 1 atmosphere = 101 325 Pa
• 1 atmosphere = 101.325 kPa
• 1 atmosphere = 760 torrs
• You can write conversion factors
between any two of these units
• Let’s practice some!

5. From HMC, p. 365 Use Dimensional Analysis!!
• The average atmospheric pressure in
Denver, Colorado is 0.830 atm. Express
this pressure in mm Hg and in kPa
• Convert a pressure of 1.75 atm to kPa
and to mm Hg.
• Convert a pressure of 570. torr to
atmospheres and to kPa.

6. The answers…

7. STP
• Standard
temperature and
pressure
• 1atmosphere
• 0 degrees Celsius
• STP is an important
concept because it
gives you a point of
reference.
• STP is also a motor
oil. That’s cool, if
irrelevant.

8. 3 labs at once!
• Put a balloon over the mouth of an
Erlenmeyer flask containing about 40 mL of
water. Place the flask on a hot plate for 10
minutes. Plunge the flask into an icewater
bath. Make observations.
• Set up the syringe in the clamps as shown.
Record the volume. Record subsequent
volumes with one book on top of the set-up,
then two, three, and 4. Graph volume as a
function of number of books.
• Heat 100 mL of water on a hotplate until it is
about 75C. Pour the water into a 2L bottle,
swirl it, dump it and cap it tightly. Observe.

9. What will you turn in?
• A graph showing
the relationship
between books and
volume of gas
• A paragraph
describing any
relationships you
have observed
between pressure,
temperature and
volume of a gas.

10. Boyle’s Law: Relating pressure and volume

11. P1V1=P2V2
• If a particular sample of gas is in a
container, pressure changes that
occur at constant temperature will
result in volume changes.
• Which of the experiments you did
deals with this?
• When you add pressure, what
happens to volume?
• Can you graph data from your lab to
quantify the relationship?

12. Charles’ Law: Relating volume and temperature

13. V1/T1=V2/T2
• If a particular sample of gas is in a
container, temperature changes that
occur at constant pressure will result in
volume changes.
• Which of the experiments you did
deals with this?
• When you increase the temperature of
a gas, what happens to volume?

14. Gay-Lussac’s Law: Relating pressure and temperature

15. Of course, these laws only work on a contained
volume of air. Coupla holes in the ‘chute, all
bets are off...

16. P1/T1=P2/T2
• If a particular sample of gas is in a
container, temperature changes that
occur at constant volume will result in
pressure changes.
• Which of the experiments you did
illustrates this?
• When you increase the temperature of
a gas, what happens to pressure?

17. Chemistry Homework due next time
• Page 348, #2, 4, 5, 7 (don’t write a
book about number 7!!)
• Page 353, 1, 3, 6, 16, 17, 18
• Read chapter 11 so you get practice
with the new vocabulary!

18. There’s just one catch...
• We can’t use the Fahrenheit or the
Celsius scale for these calculations
because they both allow the possibility
of negative values.
• You can’t have a volume of -12 liters,
or -3.4 atmospheres of pressure. For V
and P, zero is the lowest it goes. So
temperature has to be based on a
system with absolute zero.

19. Kelvin
• Theoretical
explanation
• Empirical
exploration
• The value?
• Converting to
Kelvins
• Annotating Kelvins
• Calvin vs. Kelvin!

20. Putting it all together
• The combined gas law
• Before and after scenarios on one
sample of gas
• Doing Boyle, Charles, and Gay-Lussac
problems with the combined gas law
• Using algebra on the formula before
including values
• Including labels

21. Practice!
• Boyle, pg. 370
• Charles, pg. 372
• Gay Lussac, pg. 374
• Combined gas law, pg. 375

22. Homework End of chapter 11; 9, 11, 18-32 EVEN
Can we talk about your homework for a minute…?

23. Ideal Gases and the Kinetic Molecular Theory:
a review
• Gases are composed of tiny particles
that are far apart from each other.
• Particles are in constant motion. (They
have kinetic energy.)
• We interpret their kinetic energy as
temperature.
• There is no attraction or repulsion
between particles.
• Collisions are elastic.

24. What does this mean?
• The size of a particular molecule of gas does
not determine the volume of the gas
sample.
• Higher temperature is actually just faster
molecules.
• Gas particles that are “sticky” (polar) are
less ideal than particles that are non-sticky
(like noble gases)
• Low pressure and high temperature helps
gases act more ideally, too, because they
have fewer and faster collisions.

25. Please Note!
• When heated, molecules of a gas do
not expand! They go faster, they crash
into their container more and into
each other more. Either this means
more pressure, or, if the pressure is held
constant, it means these molecules
become more spread out.
• Gases expand when heated.
Individual molecules don’t expand!

26. KE = ½ mv2
• KE is, essentially, temperature
• If 2 gas samples have the same
temperature, they have the same KE.
• If the mass of one of these gases is
higher than the mass of the other, at
the same temperature, the lighter gas
has a higher velocity.

27. Did you notice...?
• You were able to find the number of
moles of gas by converting to STP!
• We know that 1.000 moles of a gas at
273.15K and 1.000 atmospheres has a
volume of exactly 22.414 Liters
• PV/T is directly related to the number
of moles OR
• PV/T = constant “R” x number of moles
• Solve for R!

28. PV=nRT
• Clapyron, Father of
the ideal gas law
• The value you
obtain for R
depends on the
label you use for
pressure.
• The label for R is...
Atmosphere Liters per
mole Kelvin
Or... atm·L/Mol·K

29. The avanT-garde r
• Homework: Create some form of
artistic expression of the value of R and
its label.
• Purpose: To assist in the memorization
of the value and the label. To allow
students with different talents to excel.
• Secondary purpose: to lighten up and
have a little fun amidst all the math.
• Observe examples of work from
previous victims...um, students.

30. Developing the rubric as a class?
• The rubric Criterion
3 2 1 0
should
include Creativity Exemplary Adequate Limited None
creativity, ? ? ? ?
effort, and
what else? Effort
• How do we
compare Content
“pairs
projects”
with Presentation
individuals?

31. The molar mass of butane

32. Molar mass is grams per mole
• We can calculate the mass of a
sample of gas by weighing its
container before removing the gas
and after
• We can calculate number of moles by
finding the volume of a sample, the
temperature of the sample, the dry
gas pressure, and using PV=nRT. Solve
for n, number of moles.
• Grams divided by moles = molar mass!

33. Full Formal lab report…
• No hypothesis required
• Don’t forget to subtract out the water
vapor pressure
• Show calculations by hand
• Calculate molar mass and percent
error
• Describe any sources of error in your
conclusion
• Explain the water vapor issue in your
conclusion

34. In summary…
• Pressure comes in various units which you
can convert.
• KMT is the model we use to explain the
behavior of gas particles.
• Boyle, Charles, and Gay-Lussac’s laws
together make the combined gas law.
• Kelvin scale must always be used in gas law
problems
• PV=nRT
• STP provides a link between measureable
quantities and number of particles in a
sample.
• We can use gas laws to calculate molar
mass of a gas.