Piston Laboratory: Introduction

This lab will demonstrate some of the principles behind the work done on or by a gas. As a gas changes volume, work is done. In this lab, you will study how work is done by a gas in a piston.
First, design an experiment you could construct that might measure the amount of work it takes to change the volume of a gas in a piston.

  • What materials would you use?
  • What would you measure?
  • What results would you expect?
  • What if the results were different? What would that indicate?

Piston Laboratory: Description

Developing a Hypothesis:
When a gas is injected into a piston, and the pressure in the piston is held constant, the volume will change. The product of pressure and the change in volume is work.
In this lab, you will investigate how the change in volume relates to work. You will investigate the work done by two different gases, one heavy and one light.
Create a hypothesis of what you think the results of this experiment will be.

  • How will adding more gas to the piston change the work done by the piston?
  • Adding more gas will increase the height of the piston
  • How will the work done by the heavy gas differ from the work done by the lighter gas?
  • The different gases will still do the same amount of work per number of molecules
  • Students may have they will be different, if they do make sure you check to see how they explain they are the same in their discussion

Defend your hypothesis with your knowledge of work and energy. Your answers will be part of your lab write-up that you submit to your teacher.
Objectives:

  1. Generate data on how changes in the volume of a gas affect the behavior of a piston.
  2. Evaluate data generated by experimentation on the piston in terms of work and energy.

To view the items that need to be included in your lab write-up, along with a grading rubric, please refer to the Guidelines for the Laboratory section.

  1. Read the entire lab procedure and plan the steps you will take.
  2. The virtual lab can be found by clicking here.
  3. The experimental setup is comprised of a piston that you can fill with two gases: heavy molecules and light molecules. Lab experiment I is conducted to study the behavior of the piston when heavy gas molecules are sent into the cylinder, and experiment II is conducted to study the behavior of the piston when lighter gas molecules are sent into the cylinder. Notice that you can see the pressure changes on the pressure-meter on the left of the cylinder and the temperature changes on the thermometer below the pressure-meter. The pressure and temperature changes randomly when the gas is injected into the cylinder, but finally the pressure and temperature settle to a constant value since our experiment is based on finding the work done by the gas at a constant pressure. Take a few minutes and explore how this virtual lab works.
  4. In this lab, a ruler graduated in nanometer (nm) is placed at the right side of the cylinder to measure the distance (Δd) moved by the piston when the gas molecules move the piston. The constant pressure value is 0.25 atmospheric pressure as indicated by the pressure-meter.
  5. Use your spreadsheet program to build two tables like the example below. One will be for measurements with the heavy gas molecules, and the other for measurements with the lighter molecules.
    EXPERIMENT - I
    Measure the distance moved by the piston for the different number of heavier molecules, and calculate the work done by the heavier molecules.
    Area of the piston = 1x 10-16m2
    Pressure = 0.25 A t m

1 Atm = = 101 N/m2

Pressure = (0.25)(101N/m2) = = 25.25 N/m2

TABLE - 1

Trail No. / Number of Molecules / Distance moved by the piston, / Change in volume produced by the piston / Work done by the gas molecules
1 / 50 / 85 nm / 8.5 x 10-24 m3 / 2.15 x 10-22 J
2 / 300 / 510 nm / 5.10 x 10-23 m3 / 1.30 x 10-21 J
3 / 900 / 1530 / 1.530 x 10-22 m3 / 3.876 x 10-21 J
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5
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  1. EXPERIMENT - II
    Measure the distance moved by the piston for the different number of lighter molecules and calculate the work done by the lighter molecules.
    Area of the piston = 1x 10-16m2
    Pressure = 0.25 A t m
    TABLE-1

Trail No. / Number of molecules / Distance moved by the piston, / Change in volume produced by the piston / Work done by the gas molecules
1 / 50 / 85 nm / 8.5 x 10-24 m3 / 2.15 x 10-19 J
2 / 1000 / 1700 / 1.70 x 10-22m3 / 4.3 x 10-18J
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4
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  1. Begin the experiment by adding the heavy molecules of gas to the cylinder. This can be done by lifting the pump SLIGHTLY and dropping it down. Record the number of gas particles in the table I under experimentI. Use the ruler to measure the distance moved by the piston and record this value also in the table I under experiment I.
  2. Lift the pump again and add a little more gas to the cylinder. After the piston stops moving, record the distance and the number of particles of gas in the piston.
  3. Repeat Step 7 five to six times and write down the number of gas molecules in the piston and the distance moved by the piston in each trail. Record these values in Table I under experimentI. Repeat step 8 for the lighter molecules of gas, but record these values in TableI under Experiment II.
  1. Organizing Data: This laboratory measures pressure in atm, or atmospheres. You are more familiar with the SI unit pascal (Pa). Convert the pressure in the laboratory to units of pascal using the following conversion: 1 atm = 101,325 Pa. Do this calculation in your spreadsheet.
  2. Organizing Data: Calculate the change in distance (Δd) that resulted from changing the amount of gas in the piston. For any trial, the distance moved by the piston is the final position of the piston, since the initial position of the piston is always at zero.
  3. Organizing data: Convert the change in distance to meters. Notice that your measurements were in nm. 1 nm = 10-9 m.
  4. Organizing Data: The area of the piston is constant and its value is 10-16 m2. Since the piston is circular in nature, the change in volume (ΔV) can be calculated using the following formula:
    change in volume, ΔV = A*(Δd)
    Be sure to convert the distance Δd to meters before finding the change in volume.
  1. Organizing Data: Calculate the work done each time when gas is added to the piston. The equation for work done by a gas is W = P ΔV. Record these values in the last column of the table.
  2. Making Graphs: For each of the gas molecules (heavier/lighter), use a graphing program to build a graph of number of particles vs. distance. You might choose to plot the two graphs on the same axes for comparison. Be sure to include a legend if you do.

  1. Making Graphs: For each of the molecules of gas, use a graphing program to build a graph of ΔV vs W. You might choose to plot the two graphs on the same axes for comparison. Be sure to include a legend if you do.

  1. Evaluating Results: How did adding gas to the piston affect the work done by the piston?
  2. It increased it
  1. Evaluating Results: How do your graphs of number of particles of gas vs. change in distance differ from what you might expect? Propose some ideas that account for these differences.
  2. The result for both the heavy and the light are the same. The average kinetic energy of the molecules is the same because they are at the same temperature do the force will be the same.
  3. Interpreting Results: What is the slope of the line on the graphs of work vs. change in volume? How does that relate to the equation for work?
  4. The slope is the pressure in Pa and that is the constant for the equation W = PV
  5. Making Predictions: Using the graphs you created, predict the change in distance that would be required to perform 36.6 x 10-19 J of work by the heavy and lighter molecules of a gas.
  6. W = PV solve for V
  7. W = 36.6 x 10-19 J
  8. P = 0.25 atm = 2.5331 Pa
  9. V = 1.44 x10-22 m3
  10. V = Ah solve for h
  11. A = 1.0 x 10-16 m2
  12. 1440 nm
  13. Evaluating Observations: How did the work done by the heavy and lighter molecules of gas compare to each other? Use ideas of kinetic energy and your observations of the movement of the two molecules of gas to explain your answer.
  14. The values were the same, because they had the same average kinetic energy because they were at the same temperature

The lab report that you submit to your teacher should include:

  1. A document file (RTF) containing:
  2. Your experimental design idea and answers to the initial questions.
  3. Your hypothesis about this experiment, supported with physics concepts.
  4. Answers to the Conclusions from this experiment.
  5. Answers to the post lab questions at the end.
  6. Copy the following spreadsheet information into your document:
  7. Your data tables from your experiments along with calculations from the Analysis section.
  8. Graphs of ΔV vs. W for the two molecules of gases.

Reminder: Be sure to submit your assignment at this time.Refer to the Guidelines for the Laboratory section for directions on how to submit your assignment to your instructor.