Chemistry HP Unit 6 Gases. Learning Targets (Your exam at the end of Unit 6 will assess the following:) 6. Gases

Transcription

1 Chemistry HP Unit 6 Gases Learning Targets (Your exam at the end of Unit 6 will assess the following:) 6. Gases 6-1. Define pressure using a mathematical equation Perform calculations involving pressure, force, and area Describe how pressure is measured using a barometer Convert pressures between the units of atmospheres, Pascals, and millimeters of Mercury Perform calculations involving Dalton s Law of partial pressures Perform calculations involving Boyle s Law, Charles Law, and Gay-Lussac s Law Solve combined gas law problems List the conditions of STP Give Avogadro s Law by stating volume of one mole of gas at STP Perform calculations for gases at STP involving volume, moles, mass, and atoms/molecules Perform calculations using the Ideal Gas Law Perform stoichiometric calculations involving volume of gases both at STP and using the Ideal Gas Law. 1

2 6-1. Define pressure using a mathematical equation Perform calculations involving pressure, force, and area. Kinetic Molecular Theory The behavior of gases that we study in basic chemistry is based on the following four assumptions, known collectively as the Kinetic Molecular Theory of motion. Making these assumptions allows us to predict properties of gases that hold true most of the time. They are: 1. A gas consists of a collection of small particles that travel in straight-line motion and obey Newton's Laws. 2. Gas particles occupy no volume. 3. Collisions between particles are perfectly elastic, meaning that no energy is gained or lost during the collision. 4. There are no attractive or repulsive forces between the particles. Gas Pressure The concentration of gases is most often expressed as Gas Pressure. Pressure is defined as force per unit area. The equation for pressure is: P = pressure F = force A = area This equation can be rewritten to solve for either Force or Area as well. Atmospheric pressure is a specific type of gas pressure referring to the pressure the atmosphere exerts on us. At higher altitudes atmospheric pressure decreases. Looking at these two rectangular prisms below, we notice that the same force of gravity is acting upon them, because they each have the same weight. However, the pressure each exerts is different. The blocks on the right exert more pressure because the same force is being applied over a smaller area. 2

3 6-1. Define pressure using a mathematical equation Perform calculations involving pressure, force, and area. Sample Problem 1: If a rock exerts a force of 25 newtons over an area of 5.00 m 2, how much pressure is the rock putting on the ground? Sample Problem 2: The pressure of a nail was measured at 350 Pascals (Pa). What force is exerted by the nail if the surface area is 0.17 m 2? Now you try. Practice Problem 3: What area is covered by a box that exerts 40 newtons of force and a pressure of 20 Pa? 2 N/Pa 3

4 6-3. Describe how pressure is measured using a barometer. Reading Barometers and Manometers The barometer was developed by Evangelista Torricelli in It measures atmospheric pressure. Atmospheric pressure pushes down on the mercury in the basin, causing the column to rise. The height of the column is equal to the Atmospheric Pressure. Atmospheric Pressure, then, is measured by measuring the height of the column, and therefore it s often given in millimeters mercury (Hg). Pressure can also be measure with a manometer, which is U-shaped and measures pressure difference. There are two types of manometers, open-end and closed-end. Open-End Manometer The following is an open-end manometer. The liquid inside is usually mercury. When both sides are open to the air, the level of the liquid will be the same on both sides. When a gas of pressure P o is connected to one side, leaving the other side open to the air with a pressure P a, the pressure of the gas can be determined by taking the difference in heights between the two columns. Since the mercury column on the side open to the air with pressure P a is lower than the column on the side open to the gas, the air pressure is greater than the gas pressure. The gas pressure P o then, is P a minus H. 4

5 6-3. Describe how pressure is measured using a barometer. Closed-End Manometer A closed-end manometer is not open to the air. To read a closed-end manometer, take the difference between the heights of the two columns of mercury. Sample Problem 4: In a closed-end manometer, the mercury level was 690. mm higher on the closed end than on the gas side. What was the pressure of the gas in mm Hg? Sample Problem 5: In an open end manometer, atmospheric pressure was 760. mm Hg, and the mercury level was 120. mm higher on the right side than the left. What was the gas pressure? Atmospheric pressure = 760. mm Hg. Now you try. Practice Problem 6: Assuming that the valve is open, what pressure, in mm Hg, is the gas exerting? 5

6 Worksheet 6-1 (Learning Targets 6-1, ) Give the equation used to solve each problem and answer with the appropriate units. (1) Calculate the pressure when N of force is applied over an area m 2. (2) What is the force applied if a surface with an area of 10.0 m 2 experiences a pressure of 20.0 Pa? (3) What is the pressure if 1.20x10 4 N of force is applied to an area of 20.0 m 2? (4) Determine the force experienced if an area 12.0 m 2 is under a pressure of 4.0x10 4 Pa. (5) What is the area of a surface that experiences a force of 30 N when a pressure of 15 Pa are applied? (6) Find the area if a force of 5.0 x 10 4 N creates a pressure of 500 Pa. (7) Calculate the pressure exerted if a 800 N force is applied over 400 cm 2. Solve the following manometer problems. (8) Determine the gas pressure inside each bulb. Assume the atmospheric pressure is 755 mm Hg. (9) Draw the position and relative heights of the columns of mercury for each bulb. Assume the atmospheric pressure is 760 mm. Worksheet 6-1 (Learning Targets 6-1, ) 6

7 Answers. Pressure (1) 125 Pa (2) 180 N (3) 0.50 m 2 (4) 400 Pa (5) 2.4x10 5 N (6) 20 m 2 (7) 2.00x10 4 Pa Manometers (8) 645 mm Hg, 700 mm Hg, 1400 mm Hg. (9) 7

8 6-4. Convert pressures between the units of atmospheres, Pascals, and millimeters of Mercury. Pressure Conversions Pressure is measured in many different units, including millimeters mercury (mm Hg), atmospheres (atm), Torr, Pascals, pounds per square inch (psi) and Bar. The conversion factors among these units are as follows: A Torr is equal to mm Hg, named in order of Evangelista Torricelli, the creator of the first barometer. Sample Problem 7: The weather news gives the atmospheric pressure as 1.07 atm. What is this atmospheric pressure in mm Hg? 813 mm Hg Sample Problem 8. The atmospheric pressure in a certain location is mm Hg. What is this pressure in Pa? x 10 5 Pa. Sample Problem 9. Determine the gas pressure in atm in the open-end manometer below atm. 8

9 6-5. Perform calculations involving Dalton s Law of partial pressures. Standard Temperature and Pressure Chemists define the standard temperature and pressure of gases, abbreviated STP, as 0 ºC and 1 atm pressure. Recall that 0 ºC is equal to Kelvin. Standard Pressure = 1 atm = 760 mm Hg = kpa Dalton s Law of Partial Pressure Dalton s Law of Partial Pressure says that the total pressure of a mixture of gases equals the sum of the pressures that each would exert if it was present alone. Dalton s Law of Partial Pressure flows from Kinetic Molecular Theory. Since gas particles are assumed to not take up any volume, each gas particle has access to the entire volume of the container as if it were alone, and no other gas were present. Sample Problem 10: A mixture contains carbon dioxide with a partial pressure of 125 mm Hg, and oxygen with a partial pressure of 275 mm Hg. What is the total pressure of the mixture? 400. mm Hg. Sample Problem 11: A mixture of argon and neon has a total pressure of 1.50 atm. If the partial pressure of neon is 1.25 atm, what is the partial pressure of argon? 0.25 atm 9

10 Worksheet #6-2 (Learning Target 6-4, 6-5) (1) Pressure Conversions. Complete the following table. Atmospheres (atm) Millimeters mercury (mm Hg) Pascals (Pa) x x x 10 5 Dalton s Law Write an appropriate equation for each problem. Solve the equation and give the answer with appropriate units. (2) A mixture contains nitrogen with a partial pressure of 285 mm Hg and oxygen with a partial pressure of 135 mm Hg. What is the total pressure of the mixture? (3) A mixture contains carbon dioxide with a partial pressure of 4.5x10 4 Pa and water vapor with a partial pressure of 2.0x10 4 Pa. What is the total pressure of the mixture? (4) A mixture of neon and argon has a total pressure of 2.50 atm. If the partial pressure of argon is 1.00 atm, what is the partial pressure of neon? (5) A mixture containing nitrogen, oxygen, and carbon dioxide has a total pressure of 760 mm Hg. The pressure of nitrogen gas is 475 mm Hg and the pressure of the oxygen is 97 mm Hg. What is the pressure of the carbon dioxide? 10

11 Worksheet #6-2 (Learning Target 6-4, 6-5) Answers. Pressure Conversions. (1) Atmospheres (atm) Millimeters mercury (mm Hg) Pascals (Pa) x x x x x x x x x x 10 5 Dalton s Law (2) 420. mm Hg (3) 6.5x10 4 Pa (4) 1.50 atm (5) 188 mm Hg 11

12 6-6. Perform calculations involving Boyle s Law, Charles Law, and Gay-Lussac s Law. Boyle s Law says that gas volume is inversely proportional to gas pressure when we hold temperature constant. Inversely proportional means that, as you increase one, the other decreases, and vice versa. As you increase the pressure of a gas, its volume decreases. And as you decrease the volume of a gas its pressure increases. The reverse is also true. The equation for Boyle s Law is: This equation says that the original pressure of a gas P1 times its original volume V1 is equal to the new pressure P2 times the new volume V2. This graph illustrates this inverse relationship. Sample Problem: A sample of hydrogen at 1.5 atm had its pressure decreased to 0.50 atm, producing a new volume of 750 ml. What was its original volume? 12

13 6-6. Perform calculations involving Boyle s Law, Charles Law, and Gay-Lussac s Law. Sample Problem: A 175 ml sample of neon had its pressure changed from 75 kpa to 150 kpa. What is its new volume? Charles s Law Charles s Law says the gas volume is directly related to gas temperature. As the temperature of a gas increases, so does its volume. And as the volume of a gas increases, so does its temperature. V1 is the initial volume, T1 is the initial temperature and V2 is the new volume, and T2 is the new temperature. The following graph illustrates the direct relationship between volume and temperature as described by Charles s Law. As temperature increases, so does volume. 13

14 6-6. Perform calculations involving Boyle s Law, Charles Law, and Gay-Lussac s Law. Sample Problem. The volume of a gas at 25 ºC is 250 ml. Find its volume at standard temperature if pressure is held constant. Sample Problem L of a gas is collected at 100. K and then allowed to expand to 20.0 L. What is the new temperature in order to maintain the same pressure? Gay-Lussac s Law Gay-Lussac s Law says that gas pressure is directly proportional to gas temperature when volume is held constant. The equation is: Gay-Lussac s law says that, as you increase the pressure of a gas, its temperature also increases, if volume is held constant. As you increase the temperature of a gas, its pressure also increases. The following is a graph of gas pressure as a function of temperature. As you can see, pressure and temperature are directly related. As pressure is increased, so is temperature. 14

15 Sample problem. A cylinder contains a gas with a pressure of 125 kpa at a temperature of 200. K. Find the temperature of the gas which has a pressure of 100. kpa. Sample Problem. A container, designed to hold a pressure of 2.5 atm, is filled with 20.0 ml of air at room temperature (20 C) and standard pressure (1 atm). Will it be safe to throw this container into a fire where temperatures of 600 C will be reached? 15

16 Worksheet 6-3 (Learning Target 6-6) Name the formula used to solve each of the following problems and show your work. 1. The volume of a gas at 2.50 atm is 300. ml. If the pressure is increased to 5.00 atm, what will be the new volume? 2. The pressure of a sample of helium in a 2.0 L container is 0.98 atm. What is the new pressure if the sample is placed in a 1.0 L container? 3. If a sample of neon has a volume of 4.00 L at a pressure of 4.00 x 10 4 Pa. What will be the pressure if the volume is decreased to L? 4. A gas has a volume of 4.0 L at 37 C. What will be the resulting volume if the temperature is lowered to 10 C? 5. The volume of a sample of gas at 298 K is 5.00 L. What will be the new temperature of the gas if the volume is lowered to 2.50 L? 6. A gas at 300. K occupies a volume of 1.00 L. At what temperature will the volume increase to 1.50 L? 7. A sample of gas has a pressure of 2.0 atm and a temperature of 52 C. What will be the new pressure if the temperature is raised to 250. C? 8. A sample of gas has a pressure of 2.00 atm and a temperature of 200. K. What will be the new temperature if the pressure is decreased to 1.00 atm? 9. A sample of neon gas has a pressure of x10 4 Pa at 200. K. What will be the new pressure at 600. K? Answers. 16

17 6-7. Solve combined gas law problems. The three gas laws Charles s Law, Boyle s Law and Gay-Lussac s Law can be combined into one combined gas law relating pressure, volume and temperature of a gas. The combined gas law is: Sample Problem. Carbon dioxide occupies a 2.54 L container at STP. What will be the volume when the pressure is 150 kpa and 26 ºC? Sample Problem. The pressure of 8.40 L of nitrogen gas is decreased to one-half its original pressure, and its temperature is doubled. What is the new volume? 17

18 6-7. Solve combined gas law problems. The individual Gas Laws can be derived from the Combined Gas Law Boyle s Law Charles s Law Gay-Lussac s Law Sample Problem. Helium in a sealed syringe is compressed to a volume of 13 L. Its original volume was 21 L at 542 torr. Find the new pressure in torr. Sample Problem. A sample of oxygen occupies a volume of 150. L at 89.0 C. What will be the volume of oxygen when the temperature drops to 0.00 C? 18

19 Worksheet 6-4 (Learning Target 6-7) Combined Gas Law (1) A sample of 2.5 L of helium at 1.05 atm of pressure is expanded to 3.8 L, what is the resulting pressure? (2) A balloon contains 950 ml of air at 302 K. If the temperature is lowered to 280 K, what will be the volume of the balloon? (3) A gas cylinder has a pressure reading of 1.20 atm at 300 K. At what temperature will the pressure read 2.00 atm? (4) A hot air balloon contains 854 L of air at 25 C. What will the volume of the balloon be if the temperature is lowered to 10 C? (5) An aerosol can is under a pressure of 4.5 atm at 12 C. What pressure will the can reach if is heated to 35 C? (6) A sample of argon under 4.40x104 Pa of pressure occupies L. What volume will the sample occupy if the pressure is decreased to 1.50 x 10 4 Pa? (7) A sample of carbon dioxide occupies 10 ml at 50 C and 3.2 atm of pressure. What volume will the sample occupy at 30 C and 1.5 atm of pressure? (8) A tire occupies 6.0 L and has a pressure of 1.8 atm at 295 K. What will the pressure read if the tire has a volume of 5.9 L at 310 K? (9) A sample of 30 ml of chlorine gas under 5.4 x 10 5 Pa of pressure at -5 C is expanded to occupy 45 ml under 4.6x105 Pa of pressure. What will the temperature of the sample be? Answers: (1) 0.69 atm (2) 881 ml (3) 500 K (4) 811 L (5) 4.9 atm (6) 1.19 L (7) 20 ml (8) 1.9 atm (9) 3.4 x 10 2 K 19

20 6-8. List the conditions of STP Give Avogadro s Law by stating volume of one mole of gas at STP Perform calculations for gases at STP involving volume, moles, mass, and atoms/molecules. Molar Volume Avogadro s Hypothesis says that equal volumes of gases at the same temperature and pressure contain the same number of moles. Standard temperature and pressure (STP) is 0º C and 1 atm, respectively. The volume that 1 mole of any gaseous substance occupies at standard temperature and pressure, known as the molar volume, is L. 1 mole = L Warning: This conversion factor L = 1 mol applies ONLY to gases, and ONLY at STP. Sample Problem. How many moles are contained in 65.5 liters of CO2 gas at STP? Sample Problem. How many liters are occupied by 3.44 moles of CH4 gas at STP? 20

21 Worksheet 6-5 (Learning Targets 6-7, ) (1) (a) State the conditions of STP. (b) What volume does one mole of gas occupy at STP? What is the volume of the following gases at STP? (2) 5.40 mol O 2 (3) 3.20 x 10 2 mol CO 2 (4) mol SO 3 (5) 0.8 moles of chlorine gas How many moles are in each of the following volumes at STP? (6) 89.6 L Ne (7) 1.00 x 10 3 L C 2H 6 (8) 5.42 x 10-1 L F 2 (9) Determine the volume of 0.22 mol of methane gas at STP. (10) How many moles of argon gas are contained in 50.6 L at STP? (11) What is the mass of 105 ml of krypton gas at STP? How many atoms of krypton are contained within this volume? (12) A 1.8 L balloon at STP is filled with carbon dioxide. What is the mass of the gas contained within the balloon? How many molecules of carbon dioxide are present? 21

22 6-11. Perform calculations using the Ideal Gas Law. One mole of ANY gas at standard temperature and pressure occupies a volume of L. STP is 0 C or K, and that standard pressure is 1 atm. But what about gases that are NOT at STP? What volume do these gases take up? We can determine that using the ideal gas law. The Ideal Gas Law is: P = pressure V = volume n = number of moles of gas R = Rydberg s constant = L-atm-K -1 -mol -1 T = temperature (in Kelvin) Sample Problem. How many moles of argon are there in a 22.4 L sample of gas at 2 atm and 0 C? Sample Problem mole of carbon dioxide at 1.00 atm and 0.00 C occupies how much volume? 22

23 6-11. Perform calculations using the Ideal Gas Law. Sample Problem. How many grams of chlorine gas would occupy a volume of 35.5 L at a pressure of kpa and a temperature of 100. ºC? Sample Problem. How many grams are in a sample of oxygen gas if the pressure is 1520 mm Hg, the volume is 8200 ml and the temperature is -73 ºC? Sample Problem. Dry ice is carbon dioxide in the solid state grams of dry ice are placed into a 5.00 L evacuated chamber that is maintained at 35.1 C. What is the pressure in the chamber in kpa after all the dry ice has sublimed into CO2 gas? 23

24 Worksheet 6-6 (Learning Target 6-11) Ideal Gas Law (1) What volume is occupied by 2.45 mol of water vapor at atm and 450 K? (2) What is the pressure (in atm) of 0.65 mol of fluorine gas contained in 450 ml at 37 C? (3) How many moles of radon are contained in 200 ml flask under 7.65 x 10 5 Pa of pressure at 250 K? (4) What is the temperature if a 25.4 L balloon contains 6.24 mol of helium at 3.56 atm? (5) What is the mass of nitrogen dioxide gas contained in an 860 ml sample under 4.35 atm of pressure at -15 C? (6) What is the volume occupied by 1.24 x atoms of argon under 6.54 x10 5 Pa of pressure at 150 K? (7) What is the pressure (in Pa) if 24.5 g of hydrogen gas occupy 424 L at 12 C? Answers. (1) 106 L (2) 37 atm (3) 7.36 x 10-2 mol (4) 177 K (5) 8.13 g (6) L (7) 6.79 x 10 4 Pa 24

25 6-11. Perform calculations using the Ideal Gas Law. Ideal Gas Law and Molar Mass of a Gas The ideal gas law can be used to determine the molar mass of a gas: Molar Mass = grt PV Sample Problem. A g sample of gas occupies a volume of L at 739 mm Hg and 98 C. Calculate the molecular weight of this gas. Sample Problem. Calculate the mass, in grams, of 3.50 L of NO gas measured at 35 C and 835 mm Hg. 25

26 6-11. Perform calculations using the Ideal Gas Law. Ideal Gas Law and Density of a Gas The Ideal Gas Law can also be used to determine the density of a gas. d = Molar Mass P RT Sample Problem. What is the density of SO2 gas at 1.18 atm and 26 C? 26

27 Worksheet 6-7 (Learning Target 6-11) Applications of the Ideal Gas Law (1) A sample of a monatomic gas has a mass of g and occupies a volume of 200 ml at 1.32 atm and 20 C. Determine the molar mass of the gas. Identify the gas. molar mass: gas: (2) A sample of a diatomic gas has a density of 1.30 g/l at 45.4 kpa and 298 K. Determine the molar mass of the gas. Identify the gas. molar mass: gas: (3) A sample of gas (containing only nitrogen and fluorine) has a mass of g and a volume of L at 722 mm Hg and 400 K. Calculate the molar mass of the gas. Determine the formula for the gas. molar mass: formula: (4) A sample of gas (containing only sulfur and oxygen) has a density of 1.28 g/l at atm and 32 C. Calculate the molar mass of the gas. Determine the formula for the gas. molar mass: formula: (5) A g sample of a gas has a volume of L at atm and and 280 K. Calculate the molar mass of the gas. molar mass: (b) The g sample is analyzed and is found to have g of nitrogen and g of oxygen. Determine the empirical formula of the gas. empirical formula: (c) From the molar mass (i.e. the molecular weight) and the empirical formula, determine the molecular formula. (d) Give the name of the molecular formula. molecular formula: name: Answers: (1) 83.8 g/mol, krypton/kr (2) 70.9 g/mol, chlorine/cl 2 (3) 71.0 g/mol, NF 3 (4) 80.1 g/mol, SO 3 (5) (a) 92.0 g/mol (b) NO 2 (c) N 2O 4 (d) dinitrogen tetroxide 27

28 6-12. Perform stoichiometric calculations involving volume of gases both at STP and using the Ideal Gas Law. Gas Stoichiometry Sample Problem. Calculate the volume of chlorine gas at STP that is required to completely react with 3.50 g of silver, using the following equation: 2Ag(s) + Cl2(g) ---> 2AgCl(s) L Sample Problem. Calcium carbonate decomposes to form carbon dioxide and calcium oxide: CaCO3(s) ---> CO2(g) + CaO(s) How many grams of calcium carbonate will be needed to form 3.45 liters of carbon dioxide at 740 mm Hg and 121 C? 10. g 28

29 6-12. Perform stoichiometric calculations involving volume of gases both at STP and using the Ideal Gas Law. Sample Problem. When chlorine is added to acetylene, 1, 1, 2, 2-tetrachloroethane is formed: 2Cl2(g) + C2H2(g) ---> C2H2Cl4(g) How many liters of chlorine will be needed to make 75.0 grams of C2H2Cl4 at 1.90 atm and 30 C? 11.7 L 29

30 Worksheet 6-8 (Learning Target 6-12) (1) Hydrogen is combined with oxygen to form water. Write a balanced chemical equation for this reaction. What volume and mass of hydrogen and oxygen (at STP) would be required to produce 27.0 g of water? (2) Nitrogen monoxide reacts with oxygen to produce nitrogen dioxide. Write a balanced chemical equation for this reaction. (a) If 140 L of oxygen react at STP, what volume of and mass of nitrogen monoxide is required? What volume and mass of nitrogen dioxide (at STP) would be produced? (b) If 15.0 g of nitrogen monoxide react, what volume of and mass of oxygen (at STP) is required? What volume and mass of nitrogen dioxide (at STP) would be produced? (3) Nitrogen monoxide reacts with chlorine to form nitrosyl chloride (NOCl) at STP. Write a balanced chemical equation for this reaction. If 448 ml of nitrogen monoxide react with 336 ml of chlorine, which reactant is limiting and which is excess? What volume and mass of nitrosyl chloride will be produced (at STP)? (4) Propyne (C 3H 4) undergoes combustion with oxygen to produce carbon dioxide water and water. Write a balanced chemical equation for this reaction. If 52.0 L of propyne at 1.24 atm and 2870 ºC, what volume and mass of oxygen is required? What volume and mass of carbon dioxide water and water will be produced? (5) Carbon monoxide is combined with hydrogen to produce methanol (CH 3OH) at 5.25 x 10 6 Pa and 250 ºC. Write a balanced chemical equation for this reaction. If 450 ml of carbon monoxide react with 800 ml of hydrogen, which reactant is limiting and which is excess? What volume and mass of methanol will be produced? If the percent yield for the reaction is 90.0%, what mass of methanol will actually be produced? Answers: (1) 2H 2 + O 2 2H 2O 3.02 g and 33.6 L H g and 16.8 L O 2 (2) 2NO + O 2 2NO 2 (a) 375 g and 280 L NO 575 g and 280 L NO 2 (b) 8.00 g and 5.60 L O g and 11.2 L NO 2 (3) 2NO + Cl 2 2NOCl lim: NO ex: Cl g and L NOCl (4) C 3H 4 + 4O 2 3CO 2 + 2H 2O 32.0 g and 208 L O g and 156 L CO g and 104 L H 2O (5) CO + 2H 2 CH 3OH lim:h 2 ex: CO 15.5 g and L CH 3OH 30

31 Worksheet 6-9 (Gases Review) I. Pressure (1) Calculate the pressure when 800 N of force is applied over 40 m 2. (2) Calculate the force experienced if 500 Pa of pressure is applied over a surface of m 2. (3) Complete the following table. Atmospheres (atm) Millimeters Mercury (mm Hg) Pascals (Pa) x 10 4 II. Dalton s Law (1) A mixture contains carbon dioxide with a partial pressure of 3.45x105 Pa and oxygen with a partial pressure of 6.75x10 5 Pa. What is the total pressure of the mixture? (2) A mixture containing methane and oxygen has a total pressure of 0.78 atm. If the partial pressure of the methane is 0.34 atm, what is the partial pressure of the oxygen? III. Boyle s Law, Charles Law, Gay-Lussac s Law, and Combined Gas Law Give the name of the gas law for each problem. (1) A sample of 1.2 L of neon at 0.75 atm of pressure is expanded to 4.5 L. What is the resulting pressure? (2) A balloon contains 1.48 L of air at 23 C. What will the volume of the balloon be if the temperature is lowered to 17 C? (3) A gas cylinder has a pressure reading of 1.80 x 10 5 Pa at 300 K. At what temperature will the pressure read 2.34 x 10 5 Pa? (4) A sample of oxygen occupies 150 ml at 2.4 atm of pressure and 480 K. What volume will the sample occupy at 320 K and 4.8 atm of pressure? 31

32 IV. Avogadro s Law and Ideal Gas Law (1) How many moles of neon are contained in 280 ml at STP? What is the mass of the neon? How many atoms of neon are present? (2) What is the volume occupied by mol of xenon at atm and 485 K? (3) What is the volume occupied by 90.0 g of water vapor at 9.80x104 Pa and 11 C. V. Gas Stoichiometry (1) Oxygen dichloride decomposes into oxygen and chlorine at STP. Write a balanced chemical equation for this reaction. If 784 ml of oxygen dichloride are present, what volume and mass of oxygen and of chlorine is produced? (2) Nitrogen reacts with chlorine to produce nitrogen trichloride at 2.56 atm and 600 ºC. Write a balanced chemical equation for this reaction. If 15.0 L of nitrogen react with 42.0 L of chlorine, which reactant is limiting and which is in excess? What volume and mass of nitrogen trichloride will be produced? Answers: I. Pressure (1) 20 Pa (2) 100 N (3) Atmospheres mm Hg Pascals (Pa) x x x 10 4 II. Dalton s Law (1) 1.02 x 10 6 Pa (2) 0.44 atm III. Boyle s Law, Charles Law, Gay-Lussac s Law, and Combined Gas Law (1) 0.20 atm (2) 1.45 L (3) 390 K (4) 50 ml IV. Avogadro s Law and Ideal Gas Law (1) mol, g, 7.53 x atoms (2) 13.4 L (3) 120 L V. Gas Stoichiometry (1) 2OCl 2 O 2 + 2Cl g and L O 2, 2.48 g and L Cl 2 (2) N 2 + 3Cl 2 2NCl 3 lim: Cl 2, ex: N g and 28.0 L NCl 3 32