GAS LAWS WEBQUEST LAB

Background

We are constantly being exposed to the behavior of gases. Each time we pump up a tire, blow up a balloon, use a spray can, or experience the cooling of gases as they escape from a gas storage container, we are reminded of how gases behave with changes in temperature, volume, pressure, or number of particles. In an astronomical scale, we know that star formation involves contraction of gas clouds to produce dense, high-pressure cores capable of fusion reactions.

These labs will help your students investigate the behavior of gases due to changes in variables like volume, temperature, and number of particles.

This experience with molecular motion in gases can be extended to help students understand perpetual motion in all states of matter. Students can transfer this relationship to the change in temperature and the corresponding change in vibration of molecules in a solid.

The behavior of gases has been scientifically investigated starting with Robert Boyle's work in the 1600s, followed by Jacques Charles' and Joseph Gay-Lussac's work. Together these studies led to the so called "Gas Laws" which relate volume (V), pressure (P), temperature (T) and numbers of particles of gas. Consequently we have the following relationships:

• PxV = a temperature dependent constant - Boyle's Law
• P/T = volume dependent constant - Gay-Lussac's Law
• V/T = a pressure dependent constant - Charles' Law

Instructions:

Activity 1 - Gas Particles in Motion: Changing Volume

Students will investigate Boyle's Law, which relates the effect of changes in volume of a confined gas on pressure at constant temperature. Students will use data collected in the lab to discover that there is an inverse relationship between these two variables.

1. Go to the website below:

http://sunshine.chpc.utah.edu/javalabs/java12/gaslaws/index.htm

2. Click on Student Instruction

3. Read Gas laws: An Introduction

4. Click the Back to Gas Labs button at the bottom of the screen

5. Click on Activity 1- Changing volume Student Lab

6. Read and do all the activities. You must write down your answers for all of the analysis questions, mathematical analysis, challenge problems, interpolation and additional analysis problems in each section.

Data:

Follow the on screen instructions. Choose a temperature, increase and decrease the volume and record the pressure and volume on your data table. Do the experiment on at least 2 different temperatures.

Temperature K

Volume (ml)

Pressure (mm Hg)

P x V (use in math Analysis part)

Temperature K

Volume (ml)

Pressure (mm Hg)

P x V (use in math Analysis part)

Analysis:

Study the data you have just collected from your trials.

1. Describe the relationship between pressure of a gas and its volume. (Use a complete sentence. You might begin with something like this: As we increase the volume of a gas, the pressure...)

2. Does changing the temperature at which you do your experiment influence the relationship between pressure and volume? If yes, explain how.

3. After reviewing the data from your experiments, can you describe the relationship between pressure and volume?

4. Now, based on what you learned in the lab, explain how the plunger sticks to the wall.

Graph:

1. Create a graph for each set of data you collected. When you are finished compare them with the one here. Use the same graph, just make different colored lines.

2. Does the general shape of your graphs stay the same ?

3. What conclusion can you make from comparing your graphs with each other ?

Mathematical Relationship:

Scientists can learn more about how gases behave by analyzing the mathematical patterns in the numbers. In your lab packet record the answers to the questions below. Return to one of your data tables and see if you can find any additional patterns from the numbers.

1. Draw a third column on your data table to the right of the Pressure column,and label it P x V.
2. Multiply all the pairs of pressure and volume values and put them in your new column.
3. What do you notice about all of the products you have just created?

4. Check with your classmates on their results. How are they the same? How are they different? Can you explain the differences?

Challenge Problem: P1V1= P2V2

If the pressure of 3.5 Liters of air inside a volleyball is 800 mm Hg, and someone hits the ball during a serve and causes the volume to momentarily decrease to 3.0 Liters, what will be the new pressure during that instant?

Additional Analysis Questions

1. During the up-stroke of the piston of a lawn mower engine, the volume inside is greatly reduced. What effect does this have on the pressure of the gases inside?

2. You repaired a leak in your bike tire and your friend offered to let you connect a hose from one of his tires to the repaired tire. From what you have learned in this lesson would you expect to be able to inflate your tire? Give your reasons.

Activity 2 - Gas Particles in Motion: Changing Temperature

Students will investigate Gay-Lussac's Law, which relates how changing the temperature of a gas that is kept at constant volume affects the pressure of the gas. Using their data, students will understand that there is a direct relationship between these variables.

1. Go to the website below:

http://sunshine.chpc.utah.edu/javalabs/java12/gaslaws/index.htm

2. Click the Back to Gas Labs button at the bottom of the screen

3. Click on Activity 2- Changing temperature Student Lab

4. Read and do all the activities. You must write down your answers for all of the analysis questions, mathematical analysis, challenge problems, interpolation and additional analysis problems in each section.

Data:

Follow the on screen instructions. Choose a temperature, increase and decrease the temperature and record the pressure and temperature on your data table. Do the experiment on at least 2 different volume.

Volume ml

Pressure (mm Hg)

Temperature (K)

P x T (use in math Analysis part)

P/T (use in math analysis part)

Volume ml

Pressure (mm Hg)

Temperature (K)

P x T (use in math Analysis part)

P/T (use in math analysis part)

Analysis:

1. Describe the relationship between temperature and pressure. You might start your sentence like this: As we increased the temperature of our gas, the pressure...

2. Is the relationship "direct" or "inverse?"
Give at least two examples from your data table to support your answer.

Graph:

1. Make a graph for each of your data tables. Use the same graph, use different colored lines.

2. How does this graph compare to your first graph?

3. What are the similarities and what are the differences ?

4. Use your graph line to figure out the corresponding pressures.

Now do the reverse. Here are some values for pressure. What are the corresponding temperatures?

Mathematical Relationship

1. Go back to the data table and calculate P x T. Also calculate P/T.

2. Which do you find a constant answer?

3. Do you have similar answers with different volumes? Why?

Challenge Problem P1 = P2
T1 T2

With this equation you should be able to do the following problem:
If water vapor (gaseous form of water) in a pressure cooker (constant volume) is initially at 293 K and 700 mm Hg, what will be the pressure if the water vapor is heated to 413 K? Use Gay-Lussac's Law to calculate the answer.

Analysis Questions:

Now that you have investigated the relationship between the pressure of a gas and the temperature of a gas, you should be able to explain some of the following:

· Why is a warning placed on all spray cans stating: "do not incinerate can even if empty, and always store below 120 degrees F?"

· When you examine the tires on your bicycle before you start out in the morning, they appear slightly soft. However, after riding for several hours, they get harder.

· Why is the freshness button on your pickle jar down when you buy your pickles?

Activity 3 - Gas Particles in Motion: Changing Volume and Temperature

Students will investigate Charles' Law, which relates changes in the temperature of a confined gas kept at a constant pressure to the volume of the gas.

1. Go to the website below:

http://sunshine.chpc.utah.edu/javalabs/java12/gaslaws/index.htm

2. Click the Back to Gas Labs button at the bottom of the screen

3. Click on Activity 3- Changing volume and temperature Student Lab

4. Read and do all the activities. You must write down your answers for all of the analysis questions, mathematical analysis, challenge problems, interpolation and additional analysis problems in each section.

Data:

Follow the on screen instructions. Choose a temperature, hit record and record the volume. Choose another temperature, find the volume. Continue doing until you have 6 different temperatures.

. Pressure mm Hg

Temperature (K)

Volume (L)

V/T (use in math analysis part)

What was the independent variable (the one you changed)?

What was the dependent variable (the one that changed because of what you changed)?

Graph:

It is often valuable to analyze data by graphing the variables. Choose one of your experiments and make a graph of volume versus temperature. Usually the independent variable (the value you were able to select) goes on the horizontal axis. The dependent variable goes on the vertical axis. In this case, temperature will go on the X-axis and volume (which depended on temperature) will go on the Y-axis.

Interpreting the Graph:

1. If you heat the gas to 120 K what volume will the gas have?

2. If you heat the gas to 73 K what volume will the gas have?

3. Predict what the volume of the gas would be at 190 K and 440 K. These numbers are not on the graph, but do the best you can.

Calculations:

Draw a third column on your data table and label it V/T. For each of the rows in your data table divide the volume by the temperature and put that number in the new column. Did you get the same number each time?

Did your neighbors get the same number each time? We call this number a constant.

Problems:

V1 = V2
T1 T2

1. If a gas with a volume of 15 L is at a temperature of 10 K, what is the volume if the temperature changes to 30 K?

2. If a gas with a volume of 25 L is at a temperature of 5 Kelvin, what is the temperature if the volume has changed to 40 L?

3. If a gas with a volume of 19 L is at a temperature of 29 Kelvin, what is the temperature if the volume has changed to 27 L?

4. If you were to place your inflated balloon in the warm oven for a few minutes, what would happen to it?