Chemistry 151 College of the Canyons Week 9 – Introduction to Gases Fall 2020 Name __________________________________ Date ____________________________ Section_________________________________ INTRODUCTION The behavior of any gas can be described by four properties: pressure (P), temperature (T), volume (V) and amount of substance (moles, represented by the letter n). There are many relationships, or laws, that are used to investigate the behavior of gases, when one or more of these properties stay constant, while one or more of these properties change. The gas laws that we will be investigating in this lab are Boyle’s Law, Charles’ Law, Avogadro’s Law, and the Combined Gas Law. The first quantitative studies of the relationship between these properties were conducted by Robert Boyle in the mid-17th century. Boyle studied that the relationship between the pressure (P) applied to a gas and its volume (V), and demonstrated that these two properties have an inverse relationship. Thus, any increase in pressure results in an equal decrease in volume and vice versa, as long as the temperature and quantity of the gas remain constant. Boyle’s law is represented by 𝑃𝑃1 𝑉𝑉1 = 𝑃𝑃2 𝑉𝑉2 where P1 and V1 are the initial pressure and volume of the gas, and P2 and V2 are the final volume and pressure. The significance of the 1/273 value was demonstrated in 1845 by William Thomson, later known as Lord Kelvin. He proposed that if one were to continue to decrease the temperature a gas, it volume would theoretically become zero at -273oC. Of course, the volume cannot actually reach zero, but Thomson used this idea to predict that the lowest temperature possible must be -273oC, or more exactly, -273.15oC. This temperature later became known as absolute zero, and the temperature scale based on this value as the zero point is called the Kelvin scale. The units on the Kelvin temperature scale are called Kelvins. The temperature units on the two scales are the same; they differ only by their zero points. And since zero Kelvin is equal to -273.15oC, any Celsius temperature can be converted to the corresponding Kelvin temperature by simply adding 273.15 to the Celsius temperature. K = oC + 273.15 According to the Kinetic-Molecular Theory of Gases, as the temperature of a gas increases, so does the speed of the gas molecules, as the pressure and amount of gas remains constant. Charles’s observations of the relationship between the volume and temperature of a gas, now known as Charles’s Law, is stated below. V1 and T1 represent the initial volume and initial temperature of the gas, while V2 and T2 represent the final volume and final temperature of the gas. The temperatures in Charles’s Law or any of the other gas laws MUST be in units of Kelvins. 𝑉𝑉1 𝑉𝑉2 = 𝑇𝑇1 𝑇𝑇2 1 Chemistry 151 College of the Canyons Week 9 – Introduction to Gases Fall 2020 In the two laws above, Boyle’s Law and Charles’ Law, we investigated the properties of V, T and P. As volume is inversely proportional to pressure and directly proportional to temperature, we can also look at a sample of gas under both of these conditions, known as the Combined Gas Law. This law is represented by 𝑃𝑃1 𝑉𝑉1 𝑃𝑃2 𝑉𝑉2 = 𝑇𝑇1 𝑇𝑇2 where P1, V1, and T1 are the initial pressure, volume, and temperature of the gas, and P2, V2, and T2 are the final volume, pressure, and temperature. In the laws above, the amount of gas (n), remains constant, and is not therefore seen in the equation. However, we can also explore the changes that occur to the amount of gas as the volume of the gas is changed, as long as the temperature and pressure of the gas remains constant. This relationship is known as Avogadro’s law. This law is represented by 𝑉𝑉1 𝑉𝑉2 = 𝑛𝑛1 𝑛𝑛2 where V1 and n1 are the initial pressure and moles (amount) of the gas, and V2 and n2 are the final volume and moles (amount) of the gas. To summarize, the simple gas laws are outlined in the table below: Boyle’s Law 𝑃𝑃1 𝑉𝑉1 = 𝑃𝑃2 𝑉𝑉2 Charles’ Law 𝑉𝑉1 𝑉𝑉2 = 𝑇𝑇1 𝑇𝑇2 Combined Gas Law 𝑃𝑃1 𝑉𝑉1 𝑃𝑃2 𝑉𝑉2 = 𝑇𝑇1 𝑇𝑇2 Avogadro’s Law 𝑉𝑉1 𝑉𝑉2 = 𝑛𝑛1 𝑛𝑛2 PROCEDURE Part A: Introduction to Gases 1. Open the PhET simulation link: https://phet.colorado.edu/en/simulation/gases-intro 2. Click on ‘play’ button to enter simulation and then click on the ‘Intro’ option. 2 Chemistry 151 College of the Canyons Week 9 – Introduction to Gases Fall 2020 3. Give one pump of gas by clicking and dragging the handle up and down on the pump that is located to the bottom right of the empty box. Observe the behavior of the particles. How would you describe what is happening to the gas molecules? 4. Throughout this simulation, you will need to calculate the volume of the box by measuring the width. You can do this by clicking on the ‘Width ||’ option in the upper right hand corner. This should give you a measurement for the width of the box. a) What is the width of the box? What units is this in? b) Assuming the box is a perfect cube, the length and height of the box should be equal to the width. Using this information, calculate the volume of the box. 5. Record the current pressure, temperature and volume. Make sure you include units for each value! a) Pressure: b) Temperature: c) Volume: 6. Hold the volume of the container and the temperature of the gas constant, and add one more pump of gas to the container. What are your observations? 3 Chemistry 151 College of the Canyons Week 9 – Introduction to Gases Fall 2020 7. Determine the number of particles in the box by clicking on the green plus sign next to the word ‘Particles’ in the upper right hand corner of the simulation. The box should expand and tell you the number of particles present in the box (you should only see one type of particle present). Record the number of particles and the pressure in the data table below. Repeat this a few times, either increasing or decreasing the number of the same type of particles. Note: When you use the pump to add particles, the temperature is constant, and when you use the arrows in the particle box, the temperature is not constant. Pressure (atm) Number of Particles 7. Is there a relationship between the number of particles and the pressure of a gas? Briefly describe this relationship both quantitatively and qualitatively. Part BI: The Relationships between Pressure, Volume, and Temperature in a Gas – Keeping the Number of Particles and Volume Constant and exploring the Temperature and Pressure Relationship 1. Choose the Laws Option from the bottom of your screen. This option should be to the right of your current Intro option. 2. Give one pump of gas into the chamber. 3. Choose to hold the volume constant by selecting that option in the upper right-hand corner. 4. Record the initial temperature (in K) and pressure (in atm) in the chamber. a) Temperature (K): b) Pressure (atm): 5. Use the slider at the bottom of the simulator to add heat and double the temperature. a) Did the pressure go up or down? b) What is the new pressure in the chamber? c) What is the new temperature in the chamber? d) Record your observations of the particles. 4 Chemistry 151 College of the Canyons Week 9 – Introduction to Gases Fall 2020 6. Keeping the volume constant and the number of particles constant, change the temperature by either increasing or decreasing the temperature 100 K at a time and record the pressure. Repeat this process 4 times and record the data in the table below. Temperature (K) Pressure (atm) 7. Is there a relationship between the temperature and the pressure of a gas? Briefly describe this relationship both quantitatively and qualitatively. Part BII: The Relationships between Pressure, Volume, and Temperature in a Gas – Keeping the Number of Particles and Temperature Constant and exploring the Volume and Pressure Relationship 1. Reset the simulation by selecting the reset button in the bottom right corner of the simulation (this button is orange and looks like an arrow almost completing a circle). 2. Give one pump of gas into the chamber. 3. Choose to hold the temperature constant by selecting that option in the upper right-hand corner. 4. Record the initial pressure (in atm) in the chamber and calculate its volume like you did in Part A (click on ‘Width’ in the menu of the upper right-hand corner of the simulation). a) Pressure (atm): b) Volume (nm3): 5. Locate the handle on the left of the chamber and slide it to the right as far as it will go. a) What is the new width of the chamber? Does the volume go up or go down when you slide the handle it to the right? b) Assuming the length and height remain constant and only the width changes, calculate the new volume of the chamber. c) Did the pressure go up or down when you slide the handle to the right? Why? 5 Chemistry 151 College of the Canyons Week 9 – Introduction to Gases Fall 2020 6. Slide the handle all the way to the left as far as it will go. a) What is the new volume of the chamber? b) Did the pressure go up or down? Why? 7. Keeping the temperature and the number of particles constant, change the volume and record the pressure. You can do this by either increasing or decreasing the width of the box 1 nm at a time and recalculating the volume of the box. Repeat this process 4 times and record your data in the table below. Volume (nm3) Pressure (atm) 8. Is there a relationship between the volume and the pressure of a gas? Briefly describe this relationship quantitatively and qualitatively. 6 Chemistry 151 College of the Canyons Week 9 – Introduction to Gases Fall 2020 Part BIII: The Relationships between Pressure, Volume, and Temperature in a Gas – Keeping the Number of Particles Constant and exploring the Pressure 1. Reset the simulation by selecting the reset button in the bottom right corner of the simulation (this button is orange and looks like an arrow almost completing a circle). 2. Give one pump of gas into the chamber. 3. Choose to hold the pressure constant by selecting that option in the upper right-hand corner. 4. Record the initial temperature (in K) in and volume of the chamber. a) Temperature (K): b) Volume (nm3): 5. Use the slider at the bottom of the simulator to add heat and increase the temperature by 20 K. a) What is the new temperature of the container? b) Did the volume go up or go down? Why? c) Calculate the new volume of the container. 6. Keeping the pressure and the number of particles constant, change the temperature by either increasing or decreasing the temperature 20 K at a time and calculate the new volume each time. Repeat this process 4 times and record your data in the table below. Temperature (K) Volume (nm3) 7. Is there a relationship between the volume and the temperature of a gas? Briefly describe this relationship. 7 Chemistry 151 College of the Canyons Week 9 – Introduction to Gases Fall 2020 POST-LABORATORY QUESTIONS: To solve each of the problems below, first determine the equation you will need from the Introduction section of this lab. 1. If we have a sample of gas at 1.67 atm and 76.3°C, what would happen to the temperature if the pressure is increased to 2.32 atm? Calculate this temperature, assuming the volume stays constant at 2.00 L. 2. If a gas occupies 7.5 L at 1.00 atm, what will be the pressure if the volume is increased to 34.0 L? 3. A certain gas held at a temperature of 24.5 °C holds a volume of 285 mL. If the temperature is changed to 45.0 °C, what will be the volume of the gas? 4. If 4.6 moles of gas are contained in a volume of 1.75 L, what is the new volume if 1.4 moles are added to the container? 5. The total pressure in a 10.9-L automobile tire is 24 psi at 20.0°C. How much does the pressure in the tire rise if its temperature increases to 29.0°C and the volume remains at 10.9 L? 8 Chemistry 151 College of the Canyons Week 9 – Introduction to Gases Fall 2020 6. The initial pressure of 0.31 moles of gas in a drum is 742 torr. If gas is added to the drum and the final pressure is 759 torr, how many moles of gas are in the drum? Hint: for this problem, you do not have an equation in the Introduction section, but based on the relationship between pressure and volume, what can you determine about the relationship between pressure and number of moles? 9
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