What Is a Gas?

DeYoung, Robert Joliet Twp. H. S. - West
401 North Larkin Ave.
Joliet, IL 60435

Objectives Students will: 1) answer the question: What is a gas? 2) develop an understanding about how gases behave at the molecular level. 3) develop a mental and physical model of gas behavior at the molecular level. Equipment and Materials Various sizes and shapes of balloons Dry ice Gas less dense than air Gas denser than air 1 florence flask Poster paper Rope (4 meters/group) Marble sets (4 marbles/student plus 1 shooter/group) String (50 cm length/group) Metric Rulers Scissors Markers Molecular motion demonstrator with accessory kit (Purchased from scientific supply companies) Recommended Strategies Demonstration. Fill several balloons with a gas less dense than air. Fill one balloon with a gas denser than air. Place dry ice in a florence flask and cap the top of the flask with a balloon end. Observe and discuss demonstration. End the discussion by limiting the lesson to developing a scientific model of gas behavior at the molecular level. Review the concept of a scientific model. Review the concept of kinetic theory and the assumptions of kinetic theory. (The marbles will be used in this activity to represent gas particles.) Divide the class into groups of four students. Each group should receive the following: poster paper one group set of marbles (4 marbles/student plus 1 shooter/group) string one marker rules for marble activity (See below.) with observation section After the students have used the marbles to develop the model of a gas, write all of their observations on the chalk board. (Observations may include the following: straight line movement, some marbles move faster than others, collisions, marbles have mass, velocity, kinetic energy transferred.) Discuss how this model of a gas may be improved. (When using the marbles only the shooter and marbles that were hit moved. To improve this model all of the marbles should be in constant motion.) Use the molecular motion demonstrator on the overhead projector to show all marbles in constant motion. Add observations from the overhead projector to the previous observations. (Observations may include the following: random movement, collisions appear elastic, particles occupy shape and volume of container, particles in constant motion, particles far apart, no apparent attraction between particles.) Homework: Use the model of a gas developed in this activity to explain what changes, if any, will occur at the molecular level when 1) the temperature of a gas is a) increased; b) decreased. 2) the pressure of a gas is a) increased; b) decreased. ________________________________________________________________ Rules for marble activity 1. Place poster paper on the floor. 2. Use string and a marker to draw a circle with radius approximately 50 cm on the paper. 3. Place 4 meters of rope around the circle at some distance from the circumference to prevent marbles from rolling around the room. The rope may be repositioned to facilitate shooting. 4. Each student selects 4 marbles from the group set and places them anywhere within the circumference of the circle. 5. For the first round each student will get one turn in succession. 6. At each student's turn the shooter is positioned outside the circumference of the circle. The shooter will be used to try to knock marbles out of the circle. 7. Marbles knocked out of the circle are collected by the student who is shooting. 8. Starting with the second round students who knock marbles out of the circle may continue for another turn. 9. After each student's turn that student will give one observation which is to be recorded by all students in their group observation section. 10. If no marbles are knocked out of the circle the turn passes to the next student. 11. When no marbles remain in the circle the student with the most marbles wins. ------------------------------------------- Group Observations:
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