Objectives | Materials | Invitation to Learn | Lab Procedure | Closure

After investigating the effect of temperature changes on the pressure of a confined gas held at constant volume, students will be able to:

1. Relate the changes in temperature of gases to changes in pressure (i.e. direct relationship).
2. Explain why pressure of a gas increases as temperature rises.
3. Predict the pressure of a gas when its temperature is specified.
4. Construct a mathematical expression for the relationship between temperature and pressure (i.e. P is proportional to T when V is constant).

Preliminary Knowledge:

1. Basic math skills and some simple algebra
2. Graphing skills
3. Familiarity with the principle of the particulate nature of matter (a concept presented in the 7th grade Science Core Standards)
4. The natural motion of particles in matter
5. Common units of measurement for volume such as liters (L) and units for pressure such as mm Hg or atmospheres (atm)
6. The Kelvin temperature scale and how it relates to degrees celsius (K = C + 237)

• Computer Lab with Internet connection or a single machine and suitable projection equipment. We recommend a Pentium class computer (166 MHz, with at least 32 MB ram).
• Java-capable and enabled browser with the Java plug-in installed. For questions/assistance write <support@cosmic.utah.edu>.
• Calculator
• Lab notebook or Student Packet - This is a printable version of the lab materials (instructions, tables, questions, graph formats, and questions/problems) where students can record their lab.

1. Teachers may introduce this lab by demonstrating how the pressure in a fully inflated basketball or soccer ball changes when the ball is kept in the refrigerator or placed in a warm oven for 10-15 minutes. Pressure can be assessed by inserting a pressure gauge into the ball, or simply by feeling the ball with your hands.
2. Alternatively, this same activity can be carried out using an empty two liter bottle with an air tight lid. Students should be challenged to come up with an explanation for why the pressure seems to be greater at higher temperatures (remember that as temperature goes up, the particles move faster, have more kinetic energy, collide more frequently with the walls of the container, and hit the walls "harder"). Challenge students to suggest other ways to cause the pressure of a gas to increase. Perhaps they will suggest decreasing the volume of the container or forcing more gas into the container. Ask them to give some everyday examples of their suggestions, such as pumping up a tire.

Pre-Assessment:

Here are several questions which will gauge your students' understanding of the effect of temperature changes on the pressure of confined gas.

1. Without changing the size of a gas container, how can you increase the pressure of the gas inside the container?
2. What can you do to increase the pressure of the gases in a tea kettle?
3. How does the pressure of a gas change when the temperature changes and volume is kept constant?

Directions for teaching the lab:

Invite students to proceed to the beginning of the Student Lab. Teachers, please note that the temperature of gases must be measured in Kelvin so that the graphing and subsequent mathematical development can be kept as simple as possible. The gas particles, shown as colored dots, will be moving randomly and at constant velocity. The teacher should emphasize that the gas container, shown as a square on the screen, is actually a sliced-section of a larger cubic container. It is suggested that you have a model to try to explain what a sliced-section actually represents. This gas container can be changed to different volumes. However, the container will always have the same number of gas particles. Students will be able to vary the temperature of the gas container by clicking on the top of the mercury column of the thermometer and dragging the column up or down. The corresponding pressure will be scrolling in the pressure box as the temperature is raised or lowered. If the student wishes to save the temperature and pressure values, he or she presses the Record Data button. Remind students that they need to record the data from their experiment into their own lab notebooks before doing additional experiments with different sized containers. Finally, students should continue to the graphing and analysis sections of the student lab. It is very important that students attempt to graph their data by themselves before using the helps that are provided at the end of the student pages.

Summary:

This lesson should give students experience with manipulating variables and describing the relationships between those variables. Collecting and recording data correctly will be emphasized. Analysis of data both qualitatively and quantitatively is a major thrust of the lesson. The importance of controlling certain variables during an experiment can be emphasized.

Students should be encouraged to make connections from this lesson to some common events in their own lives.

• Why is the following warning placed on most spray cans: "Do not place in hot water or near radiators or stoves. Do not incinerate, even when empty. Do not store at temperatures above 120 degrees F"?
• Why does a car tire's pressure increase during summer months?
• Why do car or bicycle tires seem under-inflated in winter months?
• Explain how the "egg in the bottle" trick works. (Remember we can get a hard-boiled egg to enter a large gallon jug if we first heat the air in the jug, place the egg on the mouth of the jug as a seal, then cool the gases inside by spraying cool water onto the jug.)
• Explain the bumping of a lid on a pot of boiling water.

From a purely mathematical standpoint, it is expected that after completing the activities and analyzing the data, students will discover:

• There is a direct relationship between gas pressure and temperature when volume is kept constant.
• When pressure versus temperature is graphed, a straight line is obtained, and if the graph line is extrapolated back to the left it crosses the X-axis at approximately 0 Kelvin, so-called "absolute zero."
• That if a value for temperature is known, the corresponding pressure can be determined by interpolation using the graph.
• The quotient P/V is equal to a constant.
• One version of Gay-Lussac's Law, V1/T1 = V2/T2, allows the determinations of any one of the four variables in the equation if the other three are known.

Post-Assessment:

Teachers may return to the pre-assessment questions and use these same questions or construct their own post-assessment instrument. Hopefully, teachers can also include more difficult, higher-level questions in their post-assessment.

Closure activities:

In addition to the problems and questions at the end of the lab activity, students should be encouraged to conduct the following simple investigation as homework.

Blow up a small balloon with as much air as possible without bursting it. Tie a secure knot to ensure that no air escapes. Leave the balloon at room temperature for an hour or so. Then place the balloon in hot water and check the tension of the balloon's skin for several minutes. Make a scale from 1-5 (1 = very low tension and 5 = very high tension) to rate the tension of the balloon's skin. Can you explain your results?

Alternatively, this activity could have been done in the classroom as an introduction to this lesson. Small groups of students could also work on this after the lesson has been completed.

Extension activity:

Have students work in small groups, and have them imagine that they are employed with a hair spray company that packages its products in aerosol cans. A number of serious accidents have occurred from children throwing the empty cans into the fire just to watch them explode. The federal government has been pressured into signing a law saying that aerosol cans must carry a prominent warning label.

Students can:

1. Create a presentation for the general public describing the behavior of gas in an empty aerosol can when it comes in contact with fire.
2. Design a warning label to be placed on every can that is manufactured. The label should include a logo and simple but catchy wording. Have students present their work.
3. Students could create a poster advertising aerosol safety. Hang the posters where others can read them.