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Watch the AACT webinar on Modeling Instruction in Chemistry
Summary
In this activity, students will use models to predict behaviors of gas. They will conceptually and quantitatively solve problems, but the emphasis is put on the conceptual changes through modeling exercises.
Grade Level
High school
Objectives
By the end of this lesson, students should be able to
- Understand the relationship between pressure, volume, temperature, and particle quantity of a gas.
- Use models to predict how changing some variables of a gas will effect other variables, quantitatively and qualitatively.
Chemistry Topics
This lesson supports students’ understanding of
- Gas laws
- Properties of a gas
- Modeling
Time
Teacher Preparation: 20 minutes
Lesson: one class period
Materials
- White boards (optional)
Safety
No specific safety precautions need to be observed for this activity
Teacher Notes
- This activity could be done in groups with students thinking through their ideas using white boards.
- This activity accompanies an AACT webinar, Modeling Instruction in Chemistry.
For the Student
Lesson
On each of the problems below, start with the given P, V, T, or n; then make a decision as to how a change in P, V, T, or n will affect the starting quantity, and multiply by the appropriate factor. Draw particle diagrams of the initial and final conditions.
1. What would be the new pressure if 250 cm^{3} of gas at standard pressure is compressed to a volume of 150 cm^{3}? (n and T = constant)
P | T | V | n | |
Initial |
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Final | ||||
Effect |
2. The pressure in a bicycle tire is 105 psi at 25 ^{o}C in Fresno. You take the bicycle up to Huntington, where the temperature is – 5 ^{o}C. What is the pressure in the tire? (V and n = constant)
P | T | V | n | |
Initial |
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Final | ||||
Effect |
3. A sample of gas occupies 150 mL at 25 ^{o}C. What is its volume when the temperature is increased to 50 ^{o}C? (P and n = constant)
P | T | V | n | |
Initial |
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Final | ||||
Effect |
4. What would be the new volume if 250 cm^{3} of gas at 25 ^{o}C and 730 mm pressure were changed to standard conditions of temperature and pressure? (n = constant)
P | T | V | n | |
Initial |
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Final | ||||
Effect |
5. Sam’s bike tire contains 15 units of air particles and has a volume of 160 mL. Under these conditions the pressure reads 13 psi. The tire develops a leak. Now it contains 10 units of air and has contracted to a volume of 150 mL. What would the tire pressure be now?
P | T | V | n | |
Initial |
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Final | ||||
Effect |
6. A closed flask of air (0.250 L) contains 5.0 “puffs” of particles. The pressure probe on the flask reads 93 kPa. A student uses a syringe to add an additional 3.0 “puffs” of air through the stopper. Find the new pressure inside the flask.
P | T | V | n | |
Initial |
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Final | ||||
Effect |
7. A 350 mL sample of gas has a temperature of 30 ^{o}C and a pressure of 1.20 atm. What temperature would be needed for the same amount of gas to fit into a 250 mL flask at standard pressure?
P | T | V | n | |
Initial |
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Final | ||||
Effect |
8. A 475 cm^{3} sample of gas at standard temperature and pressure is allowed to expand until it occupies a volume of 600. cm^{3}. What temperature would be needed to return the gas to standard pressure?
P | T | V | n | |
Initial |
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Final | ||||
Effect |
9. The diagram below left shows a box containing gas molecules at 25 ^{o}C and 1 atm pressure. The piston is free to move.
In the box at right, sketch the arrangement of molecules and the position of the piston at standard temperature and pressure. Does the volume decrease significantly? Why or why not?