1. SCH3U, Strand f: Gases and atmospheric chemistry
Gas laws
SCH3U, Strand f: Gases and atmospheric chemistry
By Farah Farah and Vanessa Poehlmann

2. Minds On! The Mysterious Shrinking Balloon
Investigation done in pairs
Inflate a balloon and tie off the end tightly.
Use a string to measure it’s circumference.
Take turns constantly submerging the balloon in ice-cold water for approximately 15 minutes.
Measure the circumference again.
Compare the two measurements.
Why did the balloon shrink?

3. Why Did the Balloon Shrink?
A class discussion or a think-pair-share can follow the activity to develop hypothesis.
The answer is explained by GAS LAWS:
The gas inside the balloon compressed when the overall temperature of the balloon was decreased in the cold water.
Therefore, the circumference of the balloon decreased!

4. Background Knowledge: Physical Characteristics of Gases
Gases assume the volume and shape of their containers.
Gases are the most compressible state of matter.
Gases will mix evenly and completely when confined to the same container.
Gases have much lower densities than liquids and solids.

5. Background Knowledge: Pressure
Force
How does pressure affect our lives?
Give some examples of pressure from our every day life.
Have you ever felt your ears “pop” in an airplane or when driving over a hilly road?
This can be explained with pressure and the influence of gravity.
Area
Units of Pressure
1 pascal (Pa) = 1 N/m2
1 atm = 760 mmHg = 760 torr
1 atm = 101,325 Pa

6. Variables That Affect Gases
Volume (V) – the size of the container that holds the gas in liters (L).
Temperature (T) – the speed or kinetic energy of the particles in degrees Kelvin (oC +273)
Pressure (P) – The outward push of gas particles on their container in atmospheres (atm) or millimeters of mercury (mm Hg) or pounds/square inch (psi)
*Think of pressure as the number of collisions between gas particles and their container.
Moles (n) – the amount of gas.

7. sTP – Standard Temperature Pressure
The behavior of a gas depends on its temperature and the pressure at which the gas is held.
So far we have only dealt with gases at STP.
The values for Standard Temperature and Pressure are:
273o kelvin and 1 atm

8. Kinetic-Molecular Theory (KMT) describes the behavior of gases
A gas consists of very small particles.
The distances between gas particles are relatively large.
Gas particles are in constant, random motion.
Collisions between gas particles are perfectly elastic.
Average KE of particles depends only on the temperature of the gas.
There is no attractive force between particles of a gas.

9. The Gas Laws
With all of that background information, we can begin to discuss the gas laws:
Boyle’s Law
Charles’ Law
Gay-Lussac’s Law
The Combined Gas Law
The Ideal Gas Law

10. Boyle’s Law P1V1 =P2V2 Describes the Pressure-Volume Relationship.
The pressure and volume of a sample of gas at constant temperature are inversely proportional to each other.
(As one goes up, the other goes down)
P1V1 =P2V2
If 3 of the variables are known, the fourth can be calculated.
Constant temperature
Constant amount of gas

11. Charles’ Law Describes the temperature-volume relationship.
At constant pressure, the volume of a fixed amount of gas is directly proportional to its absolute temperature.
If 3 of the variables are known, the fourth can be calculated
Constant pressure
Constant amount of gas

12. Gay-Lussac’s Law Describes the Temperature-Pressure Relationship.
If a volume of a sample of gas remains constant, the temperature is directly proportional to its pressure.
If 3 of the variables are known, the fourth can be calculated
Constant volume
Constant amount of gas

13. The Combined Gas Law
If more than one variable changes, a different equation is needed to analyze the behavior of the gas.
5 of the variables must be known to calculate the 6th.

14. The Ideal Gas Law
Describes the physical behavior of an ideal gas in terms of the pressure, volume, temperature and the number of moles of gas.
Ideal gas: a gas as described by the kinetic-molecular theory.
BUT All gases “real gases”
FORTUNATELY, they behave like ideal gases under most conditions.
Only at very low temperatures and very high pressures do real gases show significant non-ideal behavior.
We assume that most gases are close to ideal
and that the ideal gas equation applies.

15. Ideal Gas Equation P-pressure V-volume n-number of moles of gas
R-ideal gas constant (universal gas constant) atm .L /mol.K
or torr .L/mol.K
T-temperature

16. Lesson Sequence Lesson 1: Physical Characteristics of Gases & Pressure
Lesson 2: Kinetic Molecular Theory & S.T.P
Lesson 3: Boyle’s Law & Charles’ Law
Lesson 4: Gay- Lussac’s Law & Combined Gas Law
Lesson 5: Ideal Gas Law

17. Curriculum Expectations
Lesson 1: Physical Characteristics of Gases & Pressure
F2.1, F2.2
Lesson 2: Kinetic Molecular Theory & S.T.P
F3.2, F3.3
Lesson 3: Boyle’s Law & Charles’ Law
F2.3, F3.5
Lesson 4: Gay- Lussac’s Law & Combined Gas Law
Lesson 5: Ideal Gas Law
F2.1, F3.5
NOTE: The Gas Laws are a very large topic and encompass almost all of
Strand F in SCH3U

18. Laboratory Experiment: Alka-Seltzer and the Ideal Gas Law
When Alka Seltzer reacts with water, CO2 gas is produced.
In this lab, students will collect the gas given off from this reaction by covering a flask with a balloon.
Using the mass difference, students will determine the mass lost by the process, and thus the mass of CO2 produced.
Students then use the ideal gas law to calculate the number of moles of gas produced, and from this, the molar mass of CO2.
Discussion questions follow the lab, including sources of error.
NOTE: Full laboratory is included in handout.

19. Class Activity: SCUBA Science
This activity brings a real-life connection to gas laws by discussing the tragic sinking of the Andrea Doria and the science of SCUBA diving.
Visit this link to view the entire activity:
To begin, students watch video clips of the Andrea Doria, and SCUBA divers that have become fascinated with diving the wreck site. Students then rotate through 4 exploration stations, as listed on the website. Through these stations they complete the Gas Laws Activities Handout.
The activity is designed to be completed in one class period. This can be done in small groups or as a whole class, if individual computers are not available. Also note that the end of the webpage lists assessment opportunities and other useful links to resources.

20. Safety Rules for Gas Laws Labs
When performing the previous lab or activity, the basic lab rules apply, as well as some special considerations for gasses:
 No eating or drinking in the lab
 Use proper safety protection
 Always clean glassware before you use it to be sure that residues are cleaned away. Add at least some water first, before adding any liquid or solid solutes.
 Read up experiment procedure.
 Any compressed gas cylinders are to be stored upright and away from high traffic areas.
 Never allow a gas cylinder to fall or strike another cylinder violently.
 Tell the instructor of any accidents immediately.
 If you smell gas, tell the instructor immediately.

21. Gizmo: Boyle’s Law and Charles’ Law
This Gizmo allows students to investigate Boyle's Law and Charles' Law by performing experiments where either temperature or pressure are held constant, while other variables change.
It also provides a great visual example, as students can see how the movement of the molecules change with changing variables.
This appeals to visual learners as well as student with spatial multiple intelligence.
Assessment opportunities are included in the student exploration guide.

22. Potential Student Difficulty: “If I can't see it, who cares?”
Many gases are invisible and odourless, so it is difficult for students to conceptualize their behavior.
It is our challenge as teachers to make the invisible world of gases seem real and relevant to our students!

23. Techniques to Help
Inquiry learning can help to make gasses “real” to students. By setting up various “exploration stations” for students to perform activities related to gas laws, they can formulate and test their own hypothesis about the behaviors of gases.
REMEMBER: Resist the temptation to give students the answers! Let them arrive there themselves!
There are many great demonstrations that bring the gas laws to life. Click on the links below to watch some great demos on youtube.
The Cartesian diver - this demonstration is a classic,
but is great for inquiry learning.
Why does the diver sink and float?
Magdeburg Hemispheres - a demonstration done with
household toilet plungers instead of actual Magdeburg
Hemispheres.

24. Misconceptions: Hot air rises?
Students are often confused about what really happens when a gas is heated or cooled. Some students will talk about attractive forces bringing molecules together on cooling, or repellant forces pushing molecules apart on heating. Some will suggest that there are somehow more molecules in heated gas, causing expansion in a heated balloon.

25. Techniques to Help Think of Dancing with the Stars . . .
To get students thinking about increasing or decreasing particle motion, an analogy can be made to a room full of people (gas molecules) dancing to music (temperature of the gas).
Think of Dancing with the Stars . . .
For waltz music (low temperature), the dancers will be gently swaying, and they won't bump up against the walls very often, or very hard.
For jive music (high temperature), they'll start dancing faster, bouncing off each other more, and running into the walls more often and harder. Either pressure will increase or the container will expand.
This analogy can be acted out by a few students, if safety is emphasized.

26. Practical Applications
SCUBA diving and decompression sickness
Discuss dissolved gasses in the human body, and how a quick change in pressure can cause them to come out of solution as bubbles.
Health Canada Air Quality Index
Discuss pollutants in our air,
as a result of mining, smelting,
car emissions, and industrial
effluents.

27. Differentiated Assessment
The culminating task for gas laws is an excellent opportunity for differentiated assessment.
Students must meet the following criteria, for one of the gas laws:
an authentic use of the gas law
a real world application of the law through a demonstration
Within these criteria, students can submit their culminating task in any form, as long as it is pre-approved by the teacher:
A class demonstration (spatial and musical)
A skit [performed live or taped] (body-kinesthetic)
A written report (linguistic)
A laboratory for other students to complete (logical/mathematical)

28. ELL Learners and Students with IEPs
Accommodations for ELL learners:
ELL students can be paired with student with strong language skills to assist them with labs and activities.
Graphical organizers can help ELL students to visualize the relationship between the different gas laws.
Visual demonstrations such as the Cartesian diver and Madgeburg spheres should be used as much as possible so ELL students can grasp the concepts visually.
Students with IEPs:
Adhere to the recommendations made on each student’s IEP.
Handouts can be given for notes.
If students require a quiet area to focus during loud laboratories or activities, a resource room can be used with alternative opportunities for assessment.

29. Resources/References
Decompression Sickness:
Health Canada Air Quality Index:
The Cartesian Diver
Air Pressure Demo with Potty Plungers
Gizmo – Boyle’s Law and Charles’ Law
SCUBA Science Acivity