Introduction to Gases Guided Inquiry

Transcription

1 Introduction to Gases Guided Inquiry Part 1 - The Kinetic Molecular Theory Adapted from a POGIL authored by Linda Padwa and David Hanson, Stony Brook University Why? The kinetic-molecular theory is a model or a mental image of how particles of matter behave. Knowledge of the kinetic-molecular theory allows us to predict the action of solids, liquids, and gases and understand how the changes of state occur. Learning Objectives Identify the basic differences between particle behavior in the solid, liquid and gaseous phases. Develop an understanding of the postulates of the kinetic-molecular theory. Success Criteria 1. Recognize the differences on the atomic-molecular level between solids, liquids, and gases. 2. Identify the origin of gas pressure. 3. Identify how temperature affects molecular motion. 4. Apply the kinetic molecular theory to predict the outcome of everyday situations. Prerequisites Temperature Pressure Volume Kinetic energy Potential energy Model 1 Representation of Atoms in Different Phases Key Questions 1. What are the key characteristics of atoms and molecules in gases, liquids, and solids? In Table 1 on the next page, describe the characteristics of particles for each phase of matter based on Model 1. Be specific with regard to spacing, the potential of particles for movement, and whether or not the particles will fill the container. 1

2 Table 1. Characteristics of the Phases of Matter SOLID LIQUID GAS SPACING POTENTIAL FOR MOVEMENT FILLING A CONTAINER 2. In which phase of matter is there the least spacing between particles? 3. In which phase of matter is there the most potential for movement? 4. Which phase of matter does not have a definite shape yet the particles will not fill the container? 5. In terms of spacing, what would be necessary to change from a solid to a liquid? What is this process called and how is this accomplished? 6. In terms of spacing, what would be necessary to change a liquid to a gas? What is this process called and how is this accomplished? 2

3 7. In terms of spacing, what would be necessary to change a liquid to a solid? What is this process called and how is this accomplished? Model 2 POSTULATES OF THE KINETIC MOLECULAR THEORY 1. Gases consist of tiny particles (atoms or molecules) 2. These particles are so small, compared with the distances between them that the volume (size) of the individual particles can be assumed to be negligible (zero). 3. The particles are in constant random motion, colliding with the walls of the container. These collisions with the walls cause the pressure exerted by the gas. 4. The particles are assumed to not attract nor repel each other. 5. The average kinetic energy of the gas particles is directly proportional to the Kelvin temperature. Key Questions 1. What causes a gas to exert pressure when confined in a container? 2. How does the total volume of gas particles compare to the volume of the space between the gas particles? 3. As the temperature of a gas decreases, what change occurs in the amount of kinetic energy? 4. What property of gas particles is measured by temperature? 5. What is the relationship between temperature and molecular motion? 3

4 6. In terms of the kinetic-molecular theory of gases, how can an increase in the temperature of a gas confined in a rigid container cause an increase in the pressure of the gas? Applications 1. There is a government warning on all aerosol cans that states: Do not store at a temperature above 120 F (50 C). a) Explain why this warning is required in terms of the relationship between temperature and pressure and the kinetic molecular theory. b) What could happen if the can were to be heated above 120 F (50 C)? 2. What would happen to a completely inflated balloon if it were taken from inside a house to the outside in the middle of January in Minnesota? Explain this prediction in terms of the Kinetic Molecular Theory. 3. Why do the manufacturers of tires suggest that tire pressure be checked before a car has been driven any distance? 4

5 Part 2 Gas Law Simulations Go to the website 1. There are four variables to describe gases. Three of them are observed in this simulation. List the four variables to describe gases: 2. Change the temperature in the simulation from low, to medium, to high. a. Observe what happens to the speed of the particles as well as the pressure. b. Which variable did you keep constant in this simulation? c. Using the kinetic-molecular theory, explain why the pressure changed when the temperature changed. 3. Change the volume of the plunger by pushing it down. a. Observe what happens to the speed of the particles as well as the pressure. b. Which variable did you keep constant in this simulation? Boyle s Law : c. Using the kinetic-molecular theory, explain why the pressure changed when the volume changed. Go to the website 1. Using the mouse, drag the plunger to a volume of 30 ml. The data should appear in a data table on screen. 2. Repeat at a volume of 25 ml, 20 ml, 15 ml, 10 ml, and 7 ml. Analysis: 1. As you decreased the volume of the plunger, what happened to the pressure? Explain why this happens in terms of the kinetic-molecular theory. 2. When you released the plunger, what happened to the volume? Explain why this happens in terms of the kinetic molecular theory. 5

6 3. Click the GRAPH button and draw a sketch of the graph in the space below or copy and paste it: 4. What is the relationship between pressure and volume? 5. Look at the graph on the screen and predict what the pressure would be if the volume was 40 ml. Charles Law: 1. Drag the temperature to about 400 Kelvin. 2. What happens to the volume of the syringe? Explain your answer in terms of the kinetic-molecular theory. 3. In the space below, draw a rough sketch of the graph or paste it in the space below: 4. Drag the temperature to about 100 Kelvin. 5. What happens to the volume of the syringe? 6. What is the relationship between temperature and volume? 6

7 Gay-Lussac Law: Go to the website 354/Ideal_Nav.swf::Ideal%20Gas%20Law%20Simulation 1. In the interactive, select Helium as the gas and then click beside Temperature so that your graph will be Pressure vs. Temperature 2. Change the temperature from high to low by sliding the temperature bar. Draw a sketch of the graph in the space below or paste it here: 3. What happens to the pressure of the container when the temperature is decreased? Now increase the temperature. What happens to the pressure? 4. Observe the motion of the particles in the container. Move the temperature back to low. What is happening to the particles? 5. How does what you observed in #4 explain what happened to the pressure change you described in #3? 6. What is the relationship between temperature and pressure? 7

8 Part 3 Conversions 1. How many mmhg are in 63.0 atm? Conversion Factors Kelvin is how many degrees Fahrenheit? 1 cm 3 = 1 ml 1 dm 3 = 1 L C is how many degrees Kelvin? 1000 Pa = 1 kpa 4. How many atm are in kpa? 1000 ml = 1 L 1 atm = 760 mm Hg 5. How many kiloliters are in 678 ml? 1 atm = 101 kpa kpa is how many Pa? 1 torr = 1 mm Hg 1000 L = 1 kl 7. Convert 876 torr into atm. 8. Convert 923 mm Hg into atm. 9. Convert 4.5 dm 3 into ml. 10. Convert 60 F into degrees Celsius. K = C F = 9/5(C) + 32 C = 5/9 (F 32) 11. Convert 349 degrees Kelvin into Celsius. 12. Convert 2 moles of hydrogen into liters. 13. Convert 6 grams of H 2 into moles of H 2. 8