# Gas Laws – Dimensional Analysis

Before starting the lab, complete the following problems. Return to lecture notes or homework if you don’t remember how to complete these.

Part A:

## Pressure vs. Volume

You will use the Gas Properties simulation on D2L to complete the following table.

• Click on the “Ideal” simulation (NOT explore, energy, or diffusion)
• Click on the green “+” sign to add particles of “air” to the container
• Use the double arrow to inject 200 Heavy (blue) particles (4 clicks)
• Do not change the number of particles in the simulation once you start collecting data
• Click the box next to the word “width”, this provides a scale that we will assume to be the volume of the container. (10.0 nm = 10.0 mL)
• Click the circle next to temperature to lock this variable.
• Click the handle on the container and drag left or right to adjust the volume of the container.
• The pressure will fluctuate, but do your best to choose the pressure reading that appears most frequently and record the pressure in the table for the following volumes: 5.0, 6.5, 8.0, 9.5, 11.0, 12.5, 14.0, and 15.0 mL.

Data Part A

 Volume (mL) Pressure (atm) Constant, k 5.0 46.7 233.5 6.5 36.3 235.95 8.0 28.7 229.6 9.5 24.5 232.75 11.0 21.6 237.6 12.5 19.1 238.75 14.0 17.0 238 15.0 15.8 237
1. Calculate the constant, k, from your data and add it to the Data Table above with correct significant figures. (Hint: Is P/V or PV for these data points constant?)
2. If the volume is doubled, what is the new pressure?

It goes down by half.

1. If the volume is halved, what is the new pressure?

It doubles.

[Insert Graphs 1 & 2 from Part A here. See Instructions.]

1. From your answers to the first two questions andthe shape of the curve in the plot of pressure vs.volume, is the relationship between pressure and volume direct or inverse?

Inverse

1. Based on your data, what will the pressure be if the volume of the container was increased to 40.0 mL? Calculate using the equation for your best-fit line.
2. Based on your data, what will the pressure be if the volume of the container was changed to 3.0 mL? Calculate using the equation for your best-fit line.
3. What experimental factors are assumed to be constant in this experiment?
4. Generating a best fit line calculates the slope of the line that “best fits” the data. Any linear equation has the general form: y = m•x + b

This corresponds to:

Another way to calculate the slope is to calculate the k value for each data pair, which you did in #1 and added to the data table.

To quantify the variation of the k values, calculate the % range of the k values in the table according to the equation: (watch your significant figures!)

1. Write a verbal statement that correctly expresses the Boyle’s law equation written above.

Part B:

### Pressure vs. Temperature

You will use the same Gas Properties simulation on D2L to complete the following table.

• Click on the orange button with the circular arrow on the bottom right of the simulation to reset the simulation.
• Click on the green “+” sign to add particles of “air” to the container
• Use the double arrow to inject 200 Heavy (blue) particles (4 clicks)
• Do not change the number of particles in the simulation once you start collecting data
• Click the circle next to Volume to lock this variable.
• Find the thermometer at the top of the container, click the down arrow to change the units to °C.
• Find the bucket located under the container. Imagine the container is being submerged in the water bucket. Click the lever in the middle and pull down (you should see ice in the bucket) and pull up (you should see fire).
• Adjust the lever on the bucket to bring the temperature of the container to 0°C and record the corresponding pressure on the table.
• Adjust the lever to 3 different temperatures and record those pressure readings on the table. (Suggestions: use higher temperatures like room temperature and “hot water”)

Data Part B

 Pressure (atm) Temperature (°C) Temperature (K) Constant, k (P / T or P•T) (Use Kelvin values for T) 21.6 0 273 23.7 30 303 26.2 63 336 29.6 104 377
1. Calculate the constant, k, from your data and add it to the Data Table above with correct significant figures. (Hint: Is P/V or PV for these data points constant?)
2. In order to perform this experiment, what two experimental factors were kept constant?

[Insert Graph 3 from Part B here. See Instructions.]

1. Based on the data and graph that you obtained for this experiment, is the relationship between gas pressure and temperature direct or inverse?
2. Predict what should happen to the pressure of a gas if the temperature is doubled.
3. Explain whether your prediction is supported by your data. Include specific data.
4. To quantify the variation of the k values, calculate the % range of the k values. Watch your significant figures!
5. Write the equation you used (above) to express the relationship between pressure and temperature (K). Use the symbols PT, and k.

[Insert Graph 4 from Part B here. See Instructions.]

Since absolute zero is the temperature at which the pressure theoretically becomes equal to zero, the temperature where the regression line (the extension of the temperature-pressure curve) intercepts the y-axis should be the Temperature for absolute zero (in Celsius). The fit of your graph above should be linear, with an equation in the form y=m x +b, where b is the y-intercept.

1. What is the value of absolute zero? Show your work using your equation for the best-fit line.

Answer the following questions in the space provided.

1. Use the Kinetic Molecular Theory to explain the relationship of volume and pressure on the molecular level. Assume temperature and moles of gas are constant as they were in this experiment.
2. Use the Kinetic Molecular Theory to explain the relationship of temperature and pressure on the molecular level. Assume volume and moles of gas are constant as they were in this experiment.

Prepare two computer-generated graphs with the data collected in Part A.

• Graph #1 : Plot Pressure vs. Volume
• Graph #2 : Plot Pressure vs. 1/Volume

For any graph that shows a linear trend, apply the linear curve fit to the data. Re-write the equation for the line in terms of experimental variables.

Introduction – Part B

Pressure vs. Temperature

Background

Gases are made up of molecules or atoms that are in constant motion and exert pressure when they collide with the walls of their container. The velocity and the number of collisions of these molecules is affected when the temperature of the gas increases or decreases.

In this experiment, you will study the relationship between the temperature of a gas sample and the pressure it exerts.

Using the apparatus shown in Figure 1, you will place an Erlenmeyer flask containing an air sample in water baths of varying temperature. Pressure will be monitored with a Gas Pressure Sensor and temperature will be monitored using a Temperature Probe. The volume of the gas sample and the number of molecules it contains will be kept constant.

Pressure and temperature data pairs will be collected during the experiment and then analyzed. From the data and graph, you will determine what kind of mathematical relationship exists between the pressure and absolute temperature of a confined gas.

You may also do the extension exercise and use your data to find a value for absolute zero on the Celsius temperature scale.

Experiment Part B: Pressure vs. Temperature

You will use the same Gas Properties simulation to complete Data Table B in the post lab (these instructions are also in the post lab)

• Click on the “Ideal” simulation (NOT explore, energy, or diffusion)
• Click on the green “+” sign to add particles of “air” to the container
• Use the double arrow to inject 200 Heavy (blue) particles (4 clicks)
• Do not change the number of particles in the simulation once you start collecting data.
• Click the circle next to Volume to lock this variable.
• Find the thermometer at the top of the container, click the down arrow to change the units to °C.
• Find the bucket located under the container. Imagine the container is being submerged in the water bucket. Click the lever in the middle and pull down (you should see ice in the bucket) and pull up (you should see fire).
• Adjust the lever on the bucket to bring the temperature of the container to 0°C and record the corresponding pressure on the table.
• Adjust the lever to 3 different temperatures and record those pressure readings on the table. (Suggestions: use higher temperatures like room temperature and “hot water”)

Complete data analysis for Part B now.

Prepare two computer-generated graphs with the data collected in Part B:

• Graph #1 : Plot Pressure vs. Temperature (using temperature in Kelvin)
• Graph #2 : Plot Temperature (in °C) vs. Pressure

For any graph that shows a linear trend, apply the linear curve fit to the data. Re-write the equation for the line in terms of experimental variables.

For graph #2, click on the trendline, and adjust the y-axis to a minimum of -350.0 and x-axis to -5.0 to display where this line crosses the y axis. You should see your line is now extended to show the y-intercept location.

Copy both graphs into your post lab and complete questions 13-20 for Part B and compete additional questions 21 & 22.

Post Lab & Submission

Turn in your completed Report Sheet into the correct assignment box on D2L.

Last Updated on November 26, 2021