Gas Properties

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Gas Properties

Purpose: To learn how gas behaves in response to changes in temperature, pressure, and volume.

Background: In this lab, you will learn about three of the four general laws that govern the behavior of gases.  For these laws, various parameters are held constant for a CONSTANT MASS of gas.  All three laws simulated here are combined into the Ideal Gas Law, which describes the relationship between volume, pressure and temperature for a given sample of an ideal gas.  Basically, the law states that for a given mass of any gas, the quantity PV/T is a constant (P is pressure, V is volume, and T is temperature).  An ideal gas is a theoretical gas composed of identical particles with negligible volume that move randomly and interact with each other only in perfectly elastic collisions.   It is an approximation that helps us to predict the behavior of real gases, but no gas is actually ideal.

Instructions:

Go to https://phet.colorado.edu/sims/html/gases-intro/latest/gases-intro_en.html

As you proceed through the directions, answer all the questions.

Click on the Laws module.

Part 1:  Boyle’s Law

You will start by exploring Boyle’s Law.  Click on Width.  The container should be 10 nm wide.  Add 50 heavy particles to the container.  ALLOW THE GAS TO SPREAD.  Under Hold Constant, toggle on Temperature.  Fill in Table A with the Pressure value at 10 nm width.  The width of the container is representative of the volume for this exercise.  For the 10 nm width, use the collision counter to determine the number of collisions in a sample period of 10 ps.  Record this data in Table A.

1. According to the Kinetic Molecular Theory, what causes pressure on the inside of the container?

2. Hypothesize: How will the following affect the pressure:

· Making the container smaller?

· Making the container larger?

Vary the volume of the container by pulling the handle.  Fill in Table A with the pressure and number of collisions data that correspond to the listed volumes.  BE SURE TO ALLOW THE GAS PARTICLES TO SPREAD OUT WITH EACH ADJUSTMENT YOU MAKE.

Table A

3.

a. Which variable did you control for this exercise?  This is the independent variable.

b. Which variable changed as a result?  This is the dependent variable.

c. What was held constant (2 properties)?

4. Generally, as volume increased, what happened to the number of collisions?  Why?

Using Excel, plot Pressure vs Volume.

· Pressure on y-axis

· Volume on x-axis

· Label each axis & add a title to the graph (Boyle’s Law)

· The shape of the graph should be a curve called a hyperbola.  Add a Power trendline.

· Show your graph to the instructor

5. Based on the shape of the graph, what is the relationship between volume and pressure for a given mass of gas?

Now, graph Pressure vs the inverse of the volume (1/V).  You can create a new column in Excel with the 1/V calculations.

· Pressure on y-axis

· 1/V on x-axis

· Label each axis and add a title to the graph

· Draw a best fit line through the data points and set the intercept to 0.

· Show your graph to the instructor

Calculate the other two columns in Table A; P x V and P/V.

6. Which is constant; P x V or P/V?

Boyle’s Law relates pressure to volume in a gas.  (Remember that you held temperature constant for this exercise, and the amount of gas doesn’t change.)

7. Explain Boyle’s Law based on your data and graph.  Write a simple equation for it.

Apply Boyle’s law to the following.

8. If a gas has a volume of 1.25 L and a pressure of 1.75 atm, what will the pressure be if the volume is changed to 3.15 L?  (Show your work)

9. A container has a volume of 5.85 L and a pressure of 4.25 atm.  What will the volume be if the container’s pressure is changed to 2.75 atm? (Show your work)

Part 2:  Gay-Lussac’s Law

Next, you will explore Gay-Lussac’s Law.  Reset the simulation.  Add 50 heavy particles to the container.  ALLOW THE GAS TO SPREAD.  Under Hold Constant, toggle on Volume.  Fill in Table B with the Pressure value at a temperature of 300 K.  Use the collision counter to determine the number of collisions in a sample period of 10 ps.  Record this data in Table B as well.

1. Hypothesize: How will the following affect the pressure:

· Increasing the temperature?

· Decreasing the temperature?

Vary the temperature by using the heat source slider beneath the container.  Fill in Table B with the pressure and number of collisions data that correspond to the listed temperatures.  BE SURE TO ALLOW THE GAS PARTICLES TO SPEAD OUT WITH EACH ADJUSTMENT YOU MAKE.

Table B

2.

a. What is the independent variable for this exercise?

b. What is the dependent variable?

c. What was held constant (2 properties)?

3. Generally, as temperature increased, what happened to the number of collisions?  Why?

Using Excel, plot Pressure vs Temperature.

· Pressure on y-axis

· Temperature on x-axis

· Label each axis & add a title to the graph (Gay-Lussac’s Law)

· Draw a best fit line through the data points and set the intercept to 0.

· Show your graph to the instructor

Calculate the other two columns in Table B; P x T and P/T.

4. Which is constant; P x T or P/T?

Gay-Lussac’s Law relates pressure to temperature in a gas.  (Remember that you held volume constant for this exercise.)

5. Explain Gay-Lussac’s law based on your data and graph.  Write a simple equation for it.

6. Decrease the temperature as far as the simulation allows.

a. What is that temperature?

b. What is the pressure?

c. Describe what happened to the motion of the particles.

7. Increase the temperature until reaching a maximum on the pressure gauge.

a. What happened to the container?

b. Describe the motion of the particles as you add heat.

Apply Gay-Lussac’s law to the following.

8. If a gas has a pressure of 1.69 atm at a temperature of 300 K, what will the pressure change to if the container is cooled to 100 K? (Show your work)

9. On the side of aerosol cans, there is warning against heating the container.  If the gas inside the container is at a pressure of 5.9 atm at room temperature (22° C), what will the pressure of the can be if the can is heated to 100° C? Remember to convert to Kelvin by adding 273 to the °C temperature. (Show your work)

Part 3a:  Charles’ Law

Next, you will explore Charles’ Law.   Reset the simulation.  Click on Width.  The container should be 10 nm wide.  Add 50 heavy particles to the container.  ALLOW THE GAS TO SPREAD.  Now, you will be holding pressure constant.  Click on Hold Constant Pressure with a changing V.  The temperature should be 300 K.  For this temperature, record the width of the container (volume) in Table C.  Use the collision counter to determine the number of collisions in a sample period of 10 ps.  Record this data in Table C as well.

1. Hypothesize: How will the following affect the volume:

· Increasing the temperature?

· Decreasing the temperature?

Vary the temperature by using the heat source slider beneath the container.  Fill in Table C with the volume and number of collisions data that correspond to the listed temperatures.  BE SURE TO ALLOW THE GAS PARTICLES TO SPEAD OUT WITH EACH ADJUSTMENT YOU MAKE.

Table C

2.

a. What is the independent variable for this exercise?

b. What is the dependent variable?

c. What was held constant (2 properties)?

3. Generally, as temperature increased, what happened to the number of collisions?  Why?

Using Excel, plot Volume vs Temperature.

· Volume on y-axis

· Temperature on x-axis

· Label each axis & add a title to the graph (Charles’ Law)

· Draw a best fit line through the data points and set the intercept to zero.

· Show your graph to the instructor.

Calculate the other two columns in Table C; V x T and V/T.

4. Which is constant; V x T or V/T?

Charles’ Law relates volume to temperature in a gas.  (Remember that you held pressure constant for this exercise.)

5. Explain Charles’ law based on your data and graph.  Write a simple equation for it.

Apply Charles’ law to the following.

6. If a gas has a volume of 1.25 L at a temperature of 300 K, what will the volume change to if the container is cooled to 200 K?  (Show your work)

7. A balloon bought in a store where the temperature is 22° C (295 K) has a volume of about 3.12 L.  The person takes the balloon outside on a hot day of a temperature is 37° C (310 K).  What is the new volume of the balloon? Be careful of the Temp Units!!! (Show your work)

Part 3b:  Calculating Absolute Zero with Charles’ Law

According to the kinetic theory of matter, molecules of a gas are so small that they can be considered to have no volume compared to their surrounding empty space.  Furthermore, the velocity of gas particles is directly proportional to the temperature of gas.  By cooling a gas, the particles slow down.  The temperature at which all motion stops is called absolute zero.  There can be no temperature value below this, so it is used as the starting point for an absolute temperature scale, the Kelvin scale.

Charles’ law, as you have just learned, states that there is a direct relationship between temperature and volume of a gas when the pressure is held constant.  In other words,

T/V = constant

This law can be used to experimentally find the value of absolute zero.  You will be using experimentally derived data and a graphing method to find the value of absolute zero in °C. A gas is placed in a cylinder under a movable piston.  A weight is placed on top, creating a constant force on the piston.  The temperature of the gas is varied and the corresponding values are recorded.  The data below is from the experiment.

Temperature (°C)	Volume (liters)	Temperature (K)	V/T
273	0.1094
100	0.0748
10	0.0568
1	0.0545
0	0.0544
-73	0.0403

Using graph paper or Excel, plot Temperature vs Volume.

· Volume (liters) on y-axis:  start at 0 and go up to 0.11

· Temperature (°C) on x-axis:  start at -300°C and go up to 300°C

· Label each axis & add a title to the graph (Absolute Zero Calculation)

· Draw a best fit line through the data points and project it until it crosses the x-axis

· Show your graph to the instructor

8. What is the equation for the line?

9. Based on your graph, what is the experimentally derived value of absolute zero in °C?  (Hint: At what temperature value does the line cross the x-axis?)

10. Show the gas follows Charles Law?  (Hint:  Convert the temperature values in the table above to the Kelvin scale and calculate the V/T ratio for each data point.  Record this data in the table above.)

Closing Questions (Keep in mind that all three laws apply to a constant mass of gas)

11. Give a real-life example of Boyle’s law in action.  Explain.

12. Give a real-life example of Gay-Lussac’s Law in action.  Explain.

13. Give a real-life example of Charles’ Law in action.  Explain.