Lab 8- Gas Laws Simulation

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Cape Fear Community College *

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130

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Chemistry

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Dec 6, 2023

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General, Organic, and Biochemistry: CHM-130 Dr. John D. Fields Lab 8: Gas Laws Simulation Gases behave very differently than solids or liquids. Because the space between the molecules of gas is much larger than the size of the molecules themselves, it allows for drastic changes in volume, pressure, and temperature. Weather balloons are a perfect example of the changes that can happen to a sample of gas. At ground level, the pressure is high and the balloon starts small, but when released the balloon reaches the stratosphere where the pressure is much lower. Because of this, the balloon expands (increases in volume) significantly (fig. 1). Figure 1. Weather Balloon at Ground Level versus Upper Atmosphere Gas Laws Gases can be measured in terms of pressure, volume, temperature, and number of molecules (or moles). These are the 4 variables that affect the behavior of a gas. That behavior was explored by multiple individuals for whom the gas laws are named: Boyle looked at the relationship of volume and pressure. Charles look at the relationship of volume and temperature. Gay-Lussac looked at how pressure and temperature are related. For each type of experiment, the scientists realized that to look at the relationship of 2 variables, the other 2 had to be kept constant. For example, Boyle made sure that temperature did not change during his experiments. He also kept the number of molecules (or moles) of gas the same by having sealed containers (like balloons). Charles kept the pressure and number of moles constant, and Gay-Lussac kept volume and number of moles constant. You will “play” with a simulation that accurately portrays the behavior of gases. As you change each variable you will notice what changes occur to the gas. For each, the change will either be inverse or direct. Inverse relationship means as one goes down the other goes up. For example, the longer you drive, the less gas remains in your car’s tank. This is an inverse relationship. A direct relationship means that as one variable increases, the other one increases as well. An example of this would be the longer you heat water on the stove, the hotter it gets. Cape Fear Community College 2021 1
General, Organic, and Biochemistry: CHM-130 Dr. John D. Fields Materials Computer with internet access Pen/pencil to write down observations Calculator Procedure For this lab, you will use the PhET gas law simulation. Click here to access it: https://phet.colorado.edu/sims/html/gases-intro/latest/gases-intro_en.html Once you click the link above, choose “Laws.” You will notice the following simulation apparatus (fig 2). You will add gas to the container using the pump handle, change the volume of the container using the volume handle on the left, change the temperature using the “bucket” at the bottom, and clicking the variables menu to the right to change which variables will remain constant for each experiment. To reset after each experiment, click the “Reset Button” in the lower right. Figure 2. PhET Gas Laws Simulation Cape Fear Community College 2021 2
General, Organic, and Biochemistry: CHM-130 Dr. John D. Fields A. Boyle’s Law 1. Add gas to the container by “pumping” the pump handle up and down 10 times. Do this using your computer’s mouse. Record the pressure displayed in the pressure gauge in Data Table 1. Make note of the units. 2. Choose “Temperature” in the variables menu to hold the temperature constant during this experiment. 3. Move the volume handle all the way to the left to increase the volume of the container. Record the new pressure. 4. Move the volume handle all the way to the right to decrease the volume of the container. Record the new pressure. 5. Note the relationship (inverse or direct) of volume and pressure under Data Table 1. 6. Click the Reset button to continue with part B. B. Charles’ Law 1. Add gas to the container by “pumping” the pump handle up and down 10 times. Record the temperature displayed in the thermometer in Data Table 2. Make note of the units. 2. Choose the “Pressure ↕V” in the variables menu to hold the pressure constant (but allow volume to change) during this experiment. 3. Move the handle on the temperature bucket up for 2 seconds to increase the temperature. Record the new temperature in Data Table 2. Also note what happens to the volume of the container. 4. Next, move the handle on the temperature bucket down for 4 seconds to decrease the temperature. Record the new temperature in Data Table 2 and note what happens to the volume of the container. 5. Note the relationship (inverse or direct) of volume and temperature under Data Table 2. 6. Click the Reset button to continue with part C. C. Gay-Lussac’s Law 1. Add gas to the container by “pumping” the pump handle up and down 10 times. Record the temperature displayed in the thermometer in Data Table 3. Record the pressure displayed on the pressure gauge in Data Table 3. Make note of the units. 2. Choose the “volume” in the variables menu to hold the volume constant during this experiment. 3. Move the handle on the temperature bucket up for 2 seconds to increase the temperature. Record the new temperature and new pressure in Data Table 3. 4. Next, move the handle on the temperature bucket down for 4 seconds to decrease the temperature. Record the new temperature and new pressure in Data Table 3. 5. Note the relationship (inverse or direct) of temperature and pressure under Data Table 3. 6. Click the Reset button to repeat any of these experiments. You can also “play” with the simulation by discovering what happens if you change various things (such as choosing a smaller sized gas molecule the red button below the pump handle). Cape Fear Community College 2021 3
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General, Organic, and Biochemistry: CHM-130 Dr. John D. Fields Data Table 1. Boyle’s Law Volume Pressure (with units) Initial Increased Decreased (At constant temperature and number of moles) Relationship of Volume and Pressure: ___________________________________________ Data Table 2. Charles’ Law Temperature change Temperature (with units) Change to Volume (increased, decreased, or remained the same) Initial Increased Decreased (At constant pressure and number of moles) Relationship of Volume and Temperature: __________________________________________ Data Table 3. Gay-Lussac’s Law Temperature change Temperature (with units) Pressure (with units) Initial Increased Decreased Cape Fear Community College 2021 4
General, Organic, and Biochemistry: CHM-130 Dr. John D. Fields (At constant volume and number of moles) Relationship of Pressure and Temperature: __________________________________________ Post-Lab Review Questions For post-lab review questions, use these forms of the Gas Law Equations: Boyle’s Law: P 1 V 1 = P 2 V 2 Charles’ Law: V 1 T 1 = V 2 T 2 Gay-Lussac’s Law: P 1 T 1 = P 2 T 2 1. A sample of gas starts with a pressure of 1.3atm and a volume of 24.5L. What is the new volume if the pressure is increased to 2.5atm? Assume constant temperature and number of moles. 2. A helium balloon that had a volume of 36.8L at room temperature (25.0 o C) was left out in the cold overnight where the temperature went down to 10.5 o C. What is the volume of the balloon at that new temperature? Assume constant pressure and number of moles. 3. A hollow steel ball contains argon at 3.5atm at 35.0 o C. What is the pressure if the temperature is raised to 68.0 o C? Assume constant volume and number of moles. Cape Fear Community College 2021 5