What is Boyle s law and how can it be demonstrated?

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1 Name: Relationship Between Gas Variables Gas Laws Simulation Introduction: Scientists in the late 1800 s noted relationships between various variables related to gases (pressure, volume, temperature), and the number of gas particles in the sample being studied. They were able to figure out that it was easier to study relationships if they varied only two parameters at a time and fixed (held constant) the others. For example, they would study the relationship between pressure and volume (variables) and held temperature constant ( fixed ). After recording the data and graphic analysis, a trend was determined. These experiments would be difficult to complete a laboratory because it is complicated to isolate the parameters. Using a gas simulation you will be able to create different scenarios and collect data for each combination. You will be working with a fellow scientist and determine the various gas laws that were created years ago. Objectives: Design experiments to measure the relationships between pressure, volume, and temperature. Create graphs based on predictions and observations. Make qualitative statements about the relationships between pressure, volume, and temperature using molecular models. Directions: Create mini experiments using the Gas Simulation (under my website: Links ): Following the instructions below, make observations based on the gas simulation on the website. To activate the activity, press run now and press keep (bottom of computer). Do not update Java, press later for the update. Part I: Gas Particle Behavior at Constant Temperature Boyle s Law In 1642 Evangelista Torricelli, who had worked as an assistant to Galileo, conducted a famous experiment demonstrating that the weight of air would support a column of mercury about 30 inches high in an inverted tube. Torricelli s experiment provided the first measurement of indivisible pressure of air. Robert Boyle, a skeptical chemist working in England, was inspired by Torricelli s experiment to measure the pressure of air when it was compressed or expanded. The results of Boyle s experiments were published in 1662 and became essentially the first gas law-a mathematical equation describing the relationship between the volume and pressure of air. What is Boyle s law and how can it be demonstrated? 1

2 Directions: 1. Slowly add gas particles to the vessel by raising the pump and bringing it down once. 2. On the right toolbar, make your constant parameter temperature. List the two variables that will be observed in this activity Constant Parameter Temperature Kelvin Independent Variable Dependent Variable 3. By moving the man on the left and the movable ruler tool (click on tools & options measurement tools-ruler), vary the volume and observe the change in pressure. Make sure you allow the temperature to readjust to the original value. Complete the following data table based on your observations: Relationship P vs. V PV= K Initial VOLUME Let s use the width (nm) to express the volume of the gas. V= 4 nm PRESSURE (atm) Read the pressure gauge and record the value Final V= 8 nm Conclusions: What type of relationship exists between pressure and volume (indirect or direct)? Label the x-axis and y- axis. Draw a graph representing the relationship. Graphic Representation Practice Problem: A sample of oxygen gas has a volume of ml when its pressure is atm. What is will the volume of the gas be at a pressure of atm if the temperature remains constant? (Using a highlighter, highlight your final answer) 2

3 Interpret Graphs Boyle s Law Study the line graph below. Volume in liters (L) is on the x-axis. Pressure in kilopascals (kpa) is on the y-axis. This graph shows the relationship between the pressure and volume of a gas described by Boyle. The drawings can help you picture the volume of the gas at specific points. The experiment was done at Standard Temperature. 1. Complete the table. Number of Gas Particles Pressure (kpa) Volume (L) V1P1 V2P2 V3P3 2. Look at the drawing at point V2P2. What happened to the volume in the cylinder? What happened to the amount of gas? 3. How did the volume of the gas change between Points V1P1 and V2P2? How did the pressure change? 4. How does an increase in the volume of a gas affect its pressure? Assume the temperature is constant. 3

4 5. What would the pressure be if the volume were 1.5 L? 6. Is the relationship between the pressure and volume of a gas a direct one or an inverse one? 7. Using the combined Gas Law below cross out the variable that was kept constant in Boyle s experiment. Practice Problems: a. A gas with a volume of 2.2 L at 140 kpa expands to fill a 4.4-L container. What is the pressure in the new container? What is the pressure in the new container? The temperature does not change. b. A balloon contains 30.0 L of helium gas at 103 kpa. What is the volume of the helium when the balloon rises to an altitude where the pressure is only 25.0 kpa? (Assume that the temperature remains constant.) c. When a piston is pushed down in a cylinder, the pressure on the gas in the cylinder increases from standard pressure to 3.7 atm. The initial volume is 23.5 L. What is the final volume? 4

5 Part II: Gas Particle Behavior at Constant Pressure Charles Law Application of the gas laws are important in physiology, meteorology, scuba diving, even hotair ballooning. Charles s law, which describes how the volume of a gas changes as it is heated or cooled, was inspired by one of these applications, the first sensational flight in history of hot air ballooning. 1. RESET: On the right toolbar, now make your constant parameter pressure. List the two variables that will be observed in this activity. Constant Parameter Pressure (Approximate) atm Independent Variable Dependent Variable 2. Using the thermometer (use the heat control to adjust temperature) and ruler, collect data to investigate the relationship between volume and temperature of a gas. Make sure you allow the pressure to readjust to the original value (constant pressure). Relationship T vs. V V/T = K TEMPERATURE VOLUME Let s use the width (nm) to express the volume of the gas. Initial 86 K nm Final 172 K nm Conclusions: What type of relationship exists between temperature and volume (indirect or direct)? Label the x-axis and y- axis. Draw a graph representing the relationship. Graphic Representation Practice Problem: A sample of neon gas occupies a volume of 752 ml at 300 K. What will the gas occupy at 355 K if the pressure remains constant? 5

6 Interpret Graphs Charles s Law Study the line graph below. This graph shows the relationship between the volume and the temperature of a gas at constant pressure. 1. Volume is the variable on the y-axis. What units are used for the volume? 2. What is the variable on the x-axis? What are the units? 3. What is the volume of the gas when the temperature is 300 K? 4. How did the values of the temperature of the gas change between T1 and T2? How did the volume change? 5. When the temperature is 600 K, what is the volume? 6. Use the volume at 600 K to predict the volume at 1200 K. Explain your answer. (Hint: How did the volume change when the temperature went from 300 K to 600 K?) 7. How does an increase in the temperature of a gas affect its volume? Assume the pressure is constant. 8. Is the relationship between the volume and temperature of a gas a direct or an inverse relationship? 6

7 9. Using the combined Gas Law below cross out the variable that was kept constant in Charles s experiment. When you use Charles s law, the temperatures must be in kelvins! Practice Problems: a. An inflated balloon has a volume of 3.85 L at 24 0 C. The balloon is placed in a refrigerator and cooled to C. What is the new volume of the balloon? Assume the pressure does not change. b. A 6.70 L sample of argon gas is in a cylinder with a piston at STP (standard temperature and pressure). If the pressure is kept constant, at what temperature will the volume of the gas be 7.30 L? c. At 31 0 C, the volume of gas in a small plastic bag is L. If you place the bag in a cooler at 12 0 C, what is the new volume? Assume the pressure is constant. d. Nitrogen gas is transferred from a 12.1 L container to a 15.2 L container at constant pressure. The temperature of the gas in the second container is C. what was the temperature in the first container? 7

8 Part III: Gas Particle Behavior at Constant Volume Gay- Lussac s Law Gay-Lussac grew up during the period of the French Revolution. This was a time when the science of chemistry also saw several changes. The French Revolution directly affected Gay- Lussac. During the revolution, his father was imprisoned and young Gay-Lussac was sent to the Ecole Polytechnique. This was an institution created by the French Revolution to nurture scientists, especially for military use. 1. RESET: On the right toolbar, now make your constant parameter Volume. List the two variables that will be observed in this activity Constant Parameter Volume Variable #1 Variable #2. Relationship T Vs. P P/T = K Initial Final Temperature 40 K 80 K Pressure (atm) (Approximate) What type of relationship exists between temperature and pressure (indirect or direct)? Label the x-axis and y- axis. Draw a graph representing the relationship. Graphic Representation Questions: 1. Using the combined Gas Law below cross out the variable that was kept constant in Gay Lussac s experiment. When you use Gay-Lussac s law, the temperatures must be in kelvins! 8

9 As the temperature of an enclosed gas increases, the pressure increases, if the volume is constant. Practice Problems: a. The gas in a container is at a pressure of 3.00 atm at 298 K. Directions on the container warn the user not to keep it in a place where the temperature exceeds 325 K. What would the gas pressure in the container be at 325 K? b. Aerosol cans carry labels warning not to incinerate (burn) the cans or store them above a certain temperature. This problem will show why it is dangerous to dispose of aerosol cans in a fire. The gas in a used aerosol can is at a pressure of 103 kpa at 25 o C. If the can is thrown onto a fire, what will the pressure be when the temperature reaches 928 o C? c. A pressure cooker containing kale and some water starts at 298 K and 101 kpa. The cooker is heated, and the pressure increases to 136 kpa. What is the final temperature inside the cooker? 9

10 Using the Combined Gas Law 1. A beach ball is partly inflated to a volume of 23.3 L. The temperature of the air in the ball is 305 K, and its pressure is kpa. A swimmer holds the ball under water in a pool, where the pressure is kpa. The volume of air in the ball decreases to 17.6 L. What happens to the temperature of the air in the ball? 2. Neon gas at STP is compressed in a rigid container to a volume of 84.6 L. What is the pressure of this gas at 88.5 L and 25 0 C? 3. A gas has a volume of 275 L at 348 K. When it is cooled to 297 K, its pressure changes to 115 kpa and its volume decreases to 263 L. What was the original pressure of the gas? 10

11 Part IV: Number of Gas Particles(Moles) and Volume: Temperature and Pressure Avogadro s Law This simulation cannot be performed. Therefore, predict the relationship. Since volume is one of the variables, that means the container holding the gas is flexible in some way and can expand or contract. Relationship Number of gas molecules(moles) versus Volume V = k n * n is the amount of gas in moles What happens to the volume of a balloon when helium from a tank is added to the balloon? What type of relationship exists between volume and number of moles (indirect or direct)? Label the x-axis and y- axis. Draw a graph representing the relationship. Graphic Representation Avogadro s law states that equal volumes of gases at the same temperature and pressure contain equal numbers of molecules. Practice Question: Which gas sample at STP has the same total number of molecules as 2.0 liters of CO2(g) at STP? (1) 5.0 L of CO2(g) (3) 3.0 L of H2S(g) (2) 2.0 L of Cl2(g) (4) 6.0 L of He(g) Which gas sample at STP has the same number of molecules as a 2.0-liter sample of Cl2(g) at STP? (1) 1.0 L of NH3(g) (3) 3.0 L of CO2(g) (2) 2.0 L of CH4(g) (4) 4.0 L of NO(g) Using dimensional analysis, determine the volume of 3 moles of neon gas at STP? (Equivalence statement: 1 mole of any gas at STP = 22.4 L) 11

12 Making Connections: Using your results, explain each of the following scenarios. Make sure to refer to which graph can be used as evidence for your answer. Also include references to pressure, temperature, and volume in your responses. 1. In terms of gas particle behavior, explain why bicycle tires seem more flat in the winter than in the summer. 2. Explain why a can of soda pop explodes if left in the hot sun. 3. A rigid container filled with a gas is placed in ice (example: Oxygen tank found in hospitals). What will happen to the pressure of the gas inside the tank? 4. An infected tooth forms an abscess (area of infected tissue) that fills with gas. The abscess puts pressure on the nerve of the tooth, causing a toothache. While waiting to see a dentist, the person with the toothache tried to relieve the pain by treating the infected area with moist heat. Will this treatment help? Why or why not? 5. Lungs expand as they fill with air. Exhaling decreases the volume of the lungs. Describe the law that explains this biological function?. 12