Unit 2: Gas Laws Introduction to Gas Laws Notes: Day Pages Description Date Completed Background: Variable 1 2 relationships and STP

Transcription

1 Mr. B s Chemistry Major Objectives: Name: Unit 2: Gas Laws Introduction to Gas Laws Notes: At the end of this unit, you should be able to: Block: 1. Describe the Kinetic Theory particularly as it relates to gases. 2. Relate kinetic energy and temperature. 3. Convert o C to K. 4. Describe what is meant by pressure as it relates to gases. 5. Convert between the various pressure units; atm, KPa, mm Hg. 6. Describe what is meant by STP and be able to use this information to do calculations. 7. Distinguish between the various gas laws - Boyle's, Charles', Gay-Lussac's, Combined, and Dalton's. 8. Relate the information studied to laboratory exercises. Classwork and Assignments Day Pages Description Date Completed Background: Variable 1 2 relationships and STP Pressure and Kinetic Molecular Theory Notes Gas Laws Notes Gas Law Practice Web Activity Gas Law s Gas Law Practice Atmospheric Pressure Pre Lab: Gas Laws Gas Lab Kinetic Theory Test Unit 2 Review 1

2 Items to KNOW STP = Standard Temperature and Pressure (0.00 C = 273 K and 1 atm) Standard Temperature = 1.00 atm = kpa = 760 mmhg = 760 torr Abbreviations atm - atmosphere ⁰C = K mm Hg - millimeters of mercury Gas Variables and Definitions: torr - another name for mm Hg Pa - Pascal (kpa = kilo Pascal) Pressure (P) K - Kelvin C - degrees Celsius Temperature (T) Volume (V) Moles (n) Equations Representing Relationships: Law Formula 2

3 Pressure and Kinetic Molecular Theory Notes What is pressure? What is force? You can think of it like weight or like a push. How much does your body push on the floor? How much do you have to push to move something across the floor? Liquids and solids exert pressure. Ex: Diving, your body is under more pressure when under water than when above it. If you are trapped under a piece of furniture you feel the pressure of the furniture on you. What does area have to do with it? Could you sleep on a bed of nails? How about just one nail? Carpenters why are screws pointy at the end instead of flat? The same force over a smaller area results in a higher pressure. Gas pressure is similar but hard to visualize. KINETIC MOLECULAR THEORY 1. Gases have a very small 2. Gases are constantly in at high speeds in random but line paths 3. Gases experience no attractions between a. All collisions between particles in a gas are perfectly. i. No attractive or repulsive forces ii. No transfer of Kinetic Energy iii. The average Kinetic Energy is dependent only on 4. The speed of a gas molecule is directly to its mass and speed. a. As the temperature increases, the speed of the gas molecule. These assumptions are good for IDEAL gases and are used quite often with little error. However, when one needs to be exact that you must account for the fact that REAL gases Have volume Experience electrostatic attractions For Introductory Chemistry, though, we will just deal with Ideal gases. 3

4 Pressure is the sum of all the forces of all the gas molecules colliding with a surface. Gas particles are in,, ; exerting pressure as they collide with the walls of the container. Therefore, the collisions, the the pressure. Gases have certain properties that can be explained by the KMT. 1. Low Density they because the molecules are moving at a high rate of speed and are not held back by electrostatic attractions as well as being spread out, they have low density. 2. Compressibility, they can be to compress because the molecules have space between them, unlike liquids and solids where there is little space between the molecules 3. Expansion, they will given the opportunity because the molecules are moving at a high rate of speed. 4. they will spread out, again because the molecules are moving at a high rate of speed, a. Example: perfume diffusing through air b. Example: Liquids also diffuse: food coloring in water 5. molecules moving at a high rate of speed will eventually collide with a hole and escape. a. Effusion is gas escaping through a hole, b. Example: air escaping through a hole in your tire 4

5 6. The word kinetic comes from a Greek word that means to move. The kinetic molecular theory is based upon the assumption that particles of matter (atoms or molecules) are in constant 7. Of the three states of matter, which one has the most kinetic energy? 8. Which state of matter has particles that are separated by the largest distance? 9. A scientific theory is an explanation of some type of natural phenomena. Theories are normally developed from careful study of the way the world behaves. Let s look at how gases behave and see if the kinetic molecular theory makes sense. 10. Compared to liquids and solids, gases tend to have densities. This can be explained because the particles of gas are. Units of pressure = SI units of pressure, named after scientist Pascal = named after scientist Torricelli = millimeters of mercury, comes from old way of measuring pressure by the height of a column of mercury open to atmosphere = atmosphere, unit most often used in chemistry. One atmosphere is what we feel experience every day. It is the standard pressure on earth. = pounds per square inch. Most often used in real life (tire pressure) 5

6 Gas Laws Problems Steps to Solve any Gas Law Problem: o Step 1: Write everything you are given in the problem. o Step 2: Which law do you want to use? (What remains constant?) o Step 3: Do your units match? If not, convert. (Temperature must always be in Kelvin) o Step 4: Plug in your values and solve. Proportional Indirectly Boyle's Law Charles Law Gay-Lussac's Law Dalton s Law of Partial Pressures Boyle's Law o As the pressure decreases, the volume increases. o Indirectly proportional o Temperature remains constant Example Problem: A balloon contains 30.0 L of helium gas at 1 atmosphere, and it rises to an altitude where the pressure is only 0.25 atm, assuming the temperature remains constant, what is the volume of the balloon at its new pressure? 6

7 Charles' Law o Lower temperature leads to a lower volume o Higher temperature leads to a higher volume o Directly proportional o Temperature must be converted to Kelvin o Pressure remains constant Example Problem: A balloon inflated in a room at 24 O C has a volume of 4.00 L. The balloon is then heated to a temperature of 58 O C what is the new volume if the pressure remains constant? Gay-Lussac's Law o Temperature always in Kelvin Scale o Volume remains constant Example Problem: Aeresol cans carry labels warning not to store them above a certain temperature. The gas in a used aerosol can is at a pressure of 1atm at 25 o C. If the can is thrown into a fire, what will the pressure be when the temperature reaches 1201 o C? The Combined Gas Law o No variable remains constant o Temperature always in Kelvin Scale Example Problem: The volume of a gas filled balloon is 30.0L at 313 K and has a pressure of 153 kpa. What would the volume be at standard temperature and pressure (STP)? 7

8 Dalton s Law of Partial Pressures Dalton s Law of Partial Pressures In a of gases, the pressure exerted by the mixture of gases is equal to the of the partial pressure of each gas. Example Air contains N 2, O 2, H 2 O, Ar, CO 2, the sum of which makes up the air pressure around us at any time. P Total = P Gas 1 + P Gas 2 + P Gas3 What is the air pressure at sea level if N 2, O 2, H 2 O, Ar, CO 2, have the following pressures 78.1 kpa kPa kPa kPa kPa? Gas Laws Practice: 1) A chemist collects 59.0 ml of sulfur dioxide gas on a day when the atmospheric pressure is atm. On the next day, the pressure has changed to atm. What will the volume of the SO 2 gas on the second day? 2) A can contains a gas with a volume of 56 ml and 20.0 C. What is the volume in the can if it is heated to 50.0 C? 3) A gas with a volume of 4.0L at a pressure of 90.0 kpa is allowed to expand until the pressure drops to 20.0 kpa. What is the new volume? 8

9 4) At a winter carnival, a balloon is filled with 5.00 L of helium at a temperature of 273 K. What will be the volume of the balloon when it is brought into a warm house at 295 K? 5) The initial temperature of a 1.00 liter sample of argon is 20.0 C. The pressure is decreased from 720 mm Hg to 360 mm Hg and the volume increases to 2.14 liters. What was the change in temperature of the argon? 6) 2.2 L of hydrogen at 6.5 atm pressure is used to fill a balloon at a final pressure of 1.15 atm. What is its final volume? 7) The pressure in an automobile tire is 200. kpa at a temperature of 25 C. At the end of a journey on a hot sunny day the pressure has risen to 223 kpa. What is the temperature of the air in the tire? 8) A sample of argon has a volume of 5.00 L and the pressure is atm. If the final temperature is 30.0 C, the final volume is 5.7 L, and the final pressure is 800. mm Hg, what was the initial temperature of the argon? 9

10 Gas Law Practice Worksheet 1. Why does air come out of a bicycle tire when you open the valve, even if the valve is pointing up? 2. Why do aerosol cans come with the warning, Contents under pressure. Do not heat.? Dalton s Law Worksheet 1) A metal tank contains three gases: oxygen, helium, and nitrogen. If the partial pressures of the three gases in the tank are 35 atm of O 2, 5 atm of N 2, and 25 atm of He, what is the total pressure inside of the tank? 2) Blast furnaces give off many unpleasant and unhealthy gases. If the total air pressure is 0.99 atm, the partial pressure of carbon dioxide is 0.05 atm, and the partial pressure of hydrogen sulfide is 0.02 atm, what is the partial pressure of the remaining air? 10

11 Charles Law Worksheet 1) The temperature inside my refrigerator is about 40 Celsius. If I place a balloon in my fridge that initially has a temperature of 220 C and a volume of 0.5 liters, what will be the volume of the balloon when it is fully cooled by my refrigerator? 2) A man heats a balloon in the oven. If the balloon initially has a volume of 0.4 liters and a temperature of 20 0C, what will the volume of the balloon be after he heats it to a temperature of 250 0C? Combined Gas Law Problems 1) If I initially have a gas at a pressure of 12 atm, a volume of 23 liters, and a temperature of 200 K, and then I raise the pressure to 14 atm and increase the temperature to 300 K, what is the new volume of the gas? 2) A gas takes up a volume of 17 liters, has a pressure of 2.3 atm, and a temperature of 299 K. If I raise the temperature to 350 K and lower the pressure to 1.5 atm, what is the new volume of the gas? 11

12 Boyle s Law 1. A gas occupies 12.3 liters at a pressure of 40.0 mm Hg. What is the volume when the pressure is increased to 60.0 mm Hg? 2. If a gas at 25.0 C occupies 3.60 liters at a pressure of 1.00 atm, what will be its volume at a pressure of 2.50 atm? 3. A gas occupies 1.56 L at 1.00 atm. What will be the volume of this gas if the pressure becomes 3.00 atm? 4. A gas occupies 11.2 liters at atm. What is the pressure if the volume becomes 15.0 L? 12

13 Atmospheric pressure is measured using a. The pressure of a gas is measured using a. o A Manometer is a device to measure the pressure of an enclosed gas sample. A common simple manometer consists of a U shaped tube of glass filled with some liquid. Typically the liquid is mercury because of its high density. o The height difference determines the pressure. Calculate the pressure inside each flask, given an atmospheric pressure of 760 mmhg. Flask Flask 200 mmhg 350 mmhg The gas in the flask has a higher pressure than 760 mmhg. The pressure is. The gas in the flask has a lower pressure than 760 mmhg. The pressure is. 13

14 Kinetic Molecular Theory Worksheet 1. The word kinetic comes from a Greek word that means to move. The kinetic molecular theory is based upon the assumption that particles of matter (atoms or molecules) are in constant 2. Of the three states of matter, which one has the most kinetic energy? 3. Which state of matter has particles that are separated by the largest distance? 4. A scientific theory is an explanation of some type of natural phenomena. Theories are normally developed from careful study of the way the world behaves. Let s look at how gases behave and see if the kinetic molecular theory makes sense. 5. Compared to liquids and solids, gases tend to have densities. This can be explained because the particles of gas are If you apply pressure to a sample of gas, it is fairly easy to its volume (think about what would happen to a balloon if you squeeze it gently). This can be explained because there is a lot of between gas particles. 7. If someone sprays perfume in one corner of the room, eventually a person on the other side of the room can smell it. This can be explained because gas particles move and than heavier gas particles.. In general, we would expect lighter gas particles to travel 8. When two gases mix together or move through each other, this process is known as. When gas particles escape out of a tiny hole in a container, this process is known as difference between these two words so you can avoid any confusion! 9. Kinetic molecular theory can be summarized as follows: a. Gas particles are in constant.. You should know the b. Gas particles are separated by relatively distances. c. When gas particles collide, they kinetic energy. d. Gas particles have attractive or repulsive forces between them. e. The kinetic energy of a gas is dependent on the of the gas.

15 Unit 2 Review: Gas Laws 1. If temperature is constant, the relationship between pressure and volume is a. Direct b. inverse 2. If pressure is constant, the relationship between temperature and volume is a. Direct b. Inverse 3. One way to increase pressure on a gas is to a. decrease temperature c. increase the number of gas particles b. increase volume d. lower the kinetic energy of the gas molecules 4. How do gas particles respond to an increase in volume? a. increase in kinetic energy and decrease in temperature b. decrease in kinetic energy and decrease in pressure c. increase in temperature and increase in pressure d. increase in kinetic energy and increase in temperature 5. If pressure of a gas is increased and its volume remains constant, what will happen to its temperature? a. Increase c. stay the same b. decrease 6. If a gases volume is decreased and pressure is constant, its temperature will a. Increase c. remain the same b. decrease 7. If the temperature of a gas remains constant but pressure is decreased, the volume will a. Increase c. remain the same b. decrease 8. Convert 2.3 atm into mmhg. a mmhg c. 2.3 mmhg b mmhg d mmhg 9. Convert 6.7 liters into milliliters. a ml c ml b ml d ml 10. The pressure of a gas is torr when its volume is ml. Calculate the pressure (in atm) if the gas is allowed to expand to ml at constant temperature. a atm c atm b atm d atm 11. The volume of a gas is increased from ml to ml by heating it. If the original temperature of the gas was 25.0 C, what will its final temperature be (in C)? a. 146 C d. 422 C b C e. 695 C c C 12. A gas exerts a pressure of one atm at standard temperature (273.0 K). What must the temperature be adjusted to for the gas to exert a pressure of 4.00 atm? (Give your answer in C) a. 205 C c. 819 C b C d C 13. A quantity of gas has a volume of liters at 17.0 C and 3.00 atm of pressure. To what volume must the gas be increased for the gas to be under STP conditions? a L d. 771 L b L e. 797 L c. 706 L 14. What are standard temperature and pressure conditions for gases? a. 0 C and 0 torr c. 273 C and 1 atm e. 0 C and 1 torr b. 0 K and 760 torr d. 0 C and 760 torr 15

16 15. If the volume of a confined gas is doubled while the temperature remains constant, what change (if any) would be observed in the pressure? a. It would be half as large. d. It would be 1/4 as large. b. It would double. e. It would remain the same. c. It would be four times as large. 16. A given mass of gas in a rigid container is heated from 100 C to 500 C. Which of the following responses best describes what will happen to the pressure of the gas? a. The pressure will decrease by a factor of five. b. The pressure will increase by a factor of five. c. The pressure will increase by a factor of about two. d. The pressure will increase by a factor of about eight. e. The pressure will increase by a factor of about twenty five. 17. Which of the following has the most molecules? a L of CH 4 at 0 C and 1.00 atm d L of CO 2 at 50 C and 1.25 atm b L of N 2 at 0 C and 1.00 atm e L of CO at 0 C and 1.25 atm c L of O 2 at 20 C and 1.00 atm 18. Avogadro stated that equal volumes of gases under the same conditions of temperature and pressure have equal a. numbers of molecules. d. atoms. b. numbers of grams. E. speeds c. molar masses. 19. What volume of CH 4 at 0 C and 1.00 atm contains the same number of molecules as 0.50 L of N 2 measured at 27 C and 1.50 atm? a L d L b L e L c L 20. If 3.0 L of helium at 20.0 C is allowed to expand to 4.4 L, with the pressure remaining the same, what is the new temperature? a. 702 C d C b. 430 C e. 55 C c. 157 C 21. At what temperature will 41.6 grams N 2 exerts a pressure of 815 torr in a 20.0 L cylinder? a. 134 K d. 337 K b. 176 K e. 400 K c. 238 K 22. A mixture of the gases neon and krypton is in a 2.00 liter container. The partial pressure of the neon is 0.40 atm and the partial pressure of the krypton is 1.20 atm. What is the mole fraction of neon? a d b e c d. e. 23. Which of the following gases has the greatest density at 0 C and 1 atm? a. N 2 d. Ne b. 0 2 e. CO c. F 2 16

17 24. What volume of O 2, collected at 22.0 C and 728 mmhg would be produced by the decomposition of 8.15 g KClO 3? 2KClO 3 (s) 2KCl(s) + 3 O 2 (g) a L d L b L e L c L 25. Ammonia gas is synthesized according to the balanced equation N 2 (g) + 3H 2 (g) 2NH 3 (g) If 15.0 liters of nitrogen are reacted with an excess of hydrogen, how many liters of ammonia could be produced? Assume all gas volumes are measured at the same temperature and pressure. a L b L c L d L e L 26. A gas has a volume of 3.4 L at 25 C, what is the final temperature if the volume increases to 4.7 L? 27. The initial pressure of a gas is 457 mm Hg, the final volume is 750 ml with a final pressure of 650 mm Hg. What is the initial volume of the gas? 28. A gas of 3.4 moles occupies a volume of 40.6 ml at 298 K, what is the pressure of the gas? 29. A gas of 1 mole has a temperature and volume at STP, the temperature of the gas is increased to 311 K. 17

18 30. At 18 C, 34.7 grams of carbon dioxide gas creates a pressure of 613 mm Hg, what is the volume of the gas? Hint: get into the correct units before you start. 31. A 3.00 L pocket of air at sea level has a pressure of 100 atm. Suppose the air pockets rise in the atmosphere to a certain height and expands to a volume of 10.0 L. What is the pressure of the air at the new volume? 32. The gas in a balloon occupies 3.50 L at 300. K. At which temperature will the balloon expand to 8.50 L? 33. A gas is collected by water; it contains 78.5 atm of nitrogen, atm of oxygen and atm of hydrogen. Determine the total pressure of this gas. 34. A weather balloon has a volume of 1750 L at 103 kpa. The balloon is released to the atmosphere. At the highest point above the ground, the pressure on the balloon is 35.0 kpa. What is the new volume of the balloon at this height? 18