1. Back Bires, 2007 Chapter 10 & 11: Gases Chapter 10: Page 300-330 Chapter 11: Page 332-359 Chlorine gas was used as a weapon in WWI

2. Back Bires, 2007 Slide 2 Kinetic Molecular Theory all matter is made up of particles (atoms) in random and constant motion. (colliding) all matter is made up of particles (atoms) in random and constant motion. (colliding) Gases have very low density Gases have very low density particles are spaced far apart. particles are spaced far apart. Gases are compressible. Gases are compressible. Extreme pressures-gases will compress until they become liquids (or solids, CO 2 ). Extreme pressures-gases will compress until they become liquids (or solids, CO 2 ). Adding heat to a system Adding heat to a system increases the temperature … increases the temperature … Temperature = measure of the average kinetic energy of the particles. Temperature = measure of the average kinetic energy of the particles. Increasing the pressure of a gas, Increasing the pressure of a gas, increases the density of the gas - the number of particles in a given space. increases the density of the gas - the number of particles in a given space.

3. Back Bires, 2007 Slide 3 Ideal and Real Gases Ideal Gas: Ideal Gas: Imaginary, perfect gas – makes calculations easier Imaginary, perfect gas – makes calculations easier Real Gas: Real Gas: Gas that actually behaves in reality… Gas that actually behaves in reality… When compressed, real gases will form liquids, and even exhibit liquid-like behaviors when still in gas form. When compressed, real gases will form liquids, and even exhibit liquid-like behaviors when still in gas form. Real gas molecules interact with each other - causing them to travel in non-linear paths and collide “inelastically.” Real gas molecules interact with each other - causing them to travel in non-linear paths and collide “inelastically.” With real gases, the size of the gas molecules effects their behavior. With real gases, the size of the gas molecules effects their behavior.  Ideal gasses Real Gasses 

4. Back Bires, 2007 Slide 4 Gases in our atmosphere Nitrogen-78% Nitrogen-78% Oxygen-21% Oxygen-21% Argon-<1% Argon-<1% Trace amounts of CO 2, Ne, He, CH 4, Kr, H 2, O 3, and others. Trace amounts of CO 2, Ne, He, CH 4, Kr, H 2, O 3, and others. Some gases function as greenhouse gases, and work to hold heat on the earth’s surface. Some gases function as greenhouse gases, and work to hold heat on the earth’s surface. Some gases function to block harmful UV radiation energy from the sun. Some gases function to block harmful UV radiation energy from the sun.

5. Back Bires, 2007 Slide 5 The Greenhouse Effect The sun’s energy travels through space and warms the surface of the earth. The sun’s energy travels through space and warms the surface of the earth. Some of the energy is reflected back into space. Some of the energy is reflected back into space. Greenhouse Gases Greenhouse Gases trap heat that would leave the atmosphere. trap heat that would leave the atmosphere. H 2 O, CH 4, and CO 2 are common greenhouse gases. H 2 O, CH 4, and CO 2 are common greenhouse gases. “Global Warming” “Global Warming” Theory that increasing levels of Greenhouse gasses is causing the global average temps to increase. Theory that increasing levels of Greenhouse gasses is causing the global average temps to increase.

6. Back Bires, 2007 Slide 6 The Ozone Layer (O 3 ) Ozone is Ozone is a corrosive poison in the Troposphere (where we live) a corrosive poison in the Troposphere (where we live) frequently created and given off from free electrical ionization. frequently created and given off from free electrical ionization. Ozone Ozone Absorbs harmful Ultraviolet (UV) energy in the stratosphere, 11km (6 miles) above us. Absorbs harmful Ultraviolet (UV) energy in the stratosphere, 11km (6 miles) above us. Note: the Ozone layer is less than 1mm thick! Note: the Ozone layer is less than 1mm thick! It is always moving, like a cloud, due to weather patterns and climate variations. It is always moving, like a cloud, due to weather patterns and climate variations. Page 778 for more info

7. Back Bires, 2007 Slide 7 Pascal’s Principle and Pressure French physician, Blaise Pascal, showed that French physician, Blaise Pascal, showed that fluids (including gasses) exert a uniform pressure on all the surfaces that they contact. fluids (including gasses) exert a uniform pressure on all the surfaces that they contact. Exerting a force on the top surface of a gas, causes that force (pressure) to be exerted on all the walls of its container. Exerting a force on the top surface of a gas, causes that force (pressure) to be exerted on all the walls of its container. Pressure is due to the particles of a gas striking a surface. We can detect pressure from billions upon billions of gas molecules striking a surface at any point in time. Pressure is due to the particles of a gas striking a surface. We can detect pressure from billions upon billions of gas molecules striking a surface at any point in time. F = Force a = area  Which exerts a greater pressure? 

8. Back Bires, 2007 Slide 8 Atmospheric pressure The weight of the atmosphere above us exerts a pressure of 10 Newtons per cm 2, The weight of the atmosphere above us exerts a pressure of 10 Newtons per cm 2, equivalent to the weight of a small brick on a surface no larger than your fingertip! equivalent to the weight of a small brick on a surface no larger than your fingertip! To feel the effect of doubling the pressure due to atmospheric pressure, you must swim down to a depth of roughly 10 meters…ouch! To feel the effect of doubling the pressure due to atmospheric pressure, you must swim down to a depth of roughly 10 meters…ouch! During aircraft flight, the cabins of jetliners are pressurized to just below 1 atmosphere … were they not, we would never be able to fly at 30,000 feet. ( WHY? ) During aircraft flight, the cabins of jetliners are pressurized to just below 1 atmosphere … were they not, we would never be able to fly at 30,000 feet. ( WHY? )

9. Back Bires, 2007 Slide 9 Pressure units… The SI unit of pressure is the Pascal, Pa, equaling one newton per square meter. The SI unit of pressure is the Pascal, Pa, equaling one newton per square meter. Earth’s air pressure at sea level ~ 100,000 Pa. 100kPa Earth’s air pressure at sea level ~ 100,000 Pa. 100kPa PSI (US) PSI (US) Pound per square inch. Atmospheric pressure at sea level is about 14.5 PSI. Pound per square inch. Atmospheric pressure at sea level is about 14.5 PSI. mmHg (EU, Asia) (AKA: Torr) mmHg (EU, Asia) (AKA: Torr) Millimeters of mercury. Millimeters of mercury. Atmospheric pressure is 760 mmHg at sea level. Atmospheric pressure is 760 mmHg at sea level. This has to due with the height of a column of liquid mercury raised in a barometer. This has to due with the height of a column of liquid mercury raised in a barometer. inHg inHg Inches of mercury. Used only in meteorology. Inches of mercury. Used only in meteorology. Atmospheric pressure is apx 30inHg. Atmospheric pressure is apx 30inHg.

10. Back Bires, 2007 Slide 10 And finally… And, finally…the atmosphere, atm And, finally…the atmosphere, atm the pressure exerted by the atmosphere at sea level, at 0 0 C. (This creates STP…) the pressure exerted by the atmosphere at sea level, at 0 0 C. (This creates STP…) Standard Temperature and Pressure: Standard Temperature and Pressure: STP STP usually used when referring to reactions with gases. STP is defined as: usually used when referring to reactions with gases. STP is defined as: 1 atm and 273.15 K 1 atm and 273.15 K 101 kPa and 273.15 K 101 kPa and 273.15 K 760 mmHg and 273.15 K 760 mmHg and 273.15 K When doing work with gases, select the STP that matches the pressure you are using. (atm in this class)

11. Back Bires, 2007 Slide 11Avogadro’s….Law(?) It was Amedeo Avogadro that investigated the relationship between gas volume and the number of particles. He found that It was Amedeo Avogadro that investigated the relationship between gas volume and the number of particles. He found that all the gases that he used, when measured out to their molecular weight, had a volume of about 22.4 liters! all the gases that he used, when measured out to their molecular weight, had a volume of about 22.4 liters! That is … equal volumes of gases have equal number of particles … That is … equal volumes of gases have equal number of particles … 6.02x10 23 molecules of almost any gas occupies 22.4 liters of space! 6.02x10 23 molecules of almost any gas occupies 22.4 liters of space! This led to the formation of a gas constant… This led to the formation of a gas constant… More about this later

12. Back Bires, 2007 Slide 12 Charles’ Law French chemist, Jacque Charles, showed that at constant pressure, French chemist, Jacque Charles, showed that at constant pressure, temperature and volume varied proportionally. That is… temperature and volume varied proportionally. That is… V / T=k (k = some constant #) V / T=k (k = some constant #) We tend to write Charles’ Law as the volumes and temperatures under two conditions: We tend to write Charles’ Law as the volumes and temperatures under two conditions: Simulation. constant volume c 1780’s

13. Back Bires, 2007 Slide 13 Boyle’s Law A young, adventurous, British aristocrat named Robert Boyle found that A young, adventurous, British aristocrat named Robert Boyle found that when temperature is kept constant, volume varies inversely proportional with pressure. That is: when temperature is kept constant, volume varies inversely proportional with pressure. That is: P V = k (constant) P V = k (constant) We tend to write Boyle’s Law as the volumes and pressures under two conditions: We tend to write Boyle’s Law as the volumes and pressures under two conditions: We’re leaving one law out… can you guess what it is? c 1660’s

14. Back Bires, 2007 Slide 14 Charles’ Law + Boyle’s Law + Avogadro’s Law = THE IDEAL GAS LAW R is the “gas constant” and numerically depends upon the pressure units used. R is the “gas constant” and numerically depends upon the pressure units used. PressureVolume (in Liters) MolesConstantTemperature (in Kelvin)

15. Back Bires, 2007 Slide 15 Gas Law Summary…

16. Back Bires, 2007 Slide 16 The Gas Constant The Gas Constant is the numerical bridge between number of moles of a gas, its temperature, and volume or pressure. The Gas Constant is the numerical bridge between number of moles of a gas, its temperature, and volume or pressure. R = 8.314 L٠kPa / mol٠K R = 8.314 L٠kPa / mol٠K R = 0.0821 L٠atm / mol٠K R = 0.0821 L٠atm / mol٠K Note that the first constant is in KILO Pascals. When given Pascals, you must first convert to kilopascals. Note that the first constant is in KILO Pascals. When given Pascals, you must first convert to kilopascals. Our calculations will be done in Atm Our calculations will be done in Atm

17. Back Bires, 2007 Slide 17 Dalton’s Law of Partial Pressures The total pressure in a system is the sum of the individual pressures exerted by each gas. The total pressure in a system is the sum of the individual pressures exerted by each gas. So, if gas A exerts a pressure of 2 units, and gas B exerts a pressure of 3 units, the total pressure of a system of equal parts of A and B, would be ? So, if gas A exerts a pressure of 2 units, and gas B exerts a pressure of 3 units, the total pressure of a system of equal parts of A and B, would be ? Total = A + B …….. 2 + 3 = 5 units. Total = A + B …….. 2 + 3 = 5 units. In our atmosphere, Oxygen is about 21%. If we have a sample of air at 1 atm, what is the pressure due to oxygen? In our atmosphere, Oxygen is about 21%. If we have a sample of air at 1 atm, what is the pressure due to oxygen?

18. Back Bires, 2007 Slide 18 Graham’s Law of Gas Effusion Effusion Effusion motion of a gas through an opening in a container. motion of a gas through an opening in a container. not Diffusion - dispersing from higher concentration to lower concentration. not Diffusion - dispersing from higher concentration to lower concentration. Rates (speeds) of effusion are related to the molar mass of a gas. Rates (speeds) of effusion are related to the molar mass of a gas. The higher the molar mass, the slower the gas will effuse. The higher the molar mass, the slower the gas will effuse. This is a property of real gases This is a property of real gases

19. Back Bires, 2007 Slide 19 Graham’s Law of Gas Effusion At the same temperature… At the same temperature… The higher the molar mass, the slower the gas will effuse. The higher the molar mass, the slower the gas will effuse. Graham’s Law of Effusion: Graham’s Law of Effusion: Gas A vs Gas B Molar mass velocity

20. Back Bires, 2007 Slide 20 Vapor Pressure All liquids exert a vapor pressure. All liquids exert a vapor pressure. Vapor pressure = liquid’s molecules  gas phase. Vapor pressure = liquid’s molecules  gas phase. Higher temperatures  greater molecular speed  greater vapor pressure. Higher temperatures  greater molecular speed  greater vapor pressure. More volatile liquids exert a greater vapor pressure than do less volatile liquids. More volatile liquids exert a greater vapor pressure than do less volatile liquids. Can you explain why this is? Can you explain why this is? In lab: we collect gasses over water. There is a small amount of water vapor in our gas samples, due to water’s vapor pressure. In lab: we collect gasses over water. There is a small amount of water vapor in our gas samples, due to water’s vapor pressure. Page 324

21. Back Bires, 2007 Slide 21 Phase Diagrams Phase diagrams Phase diagrams predict if a substance will be a solid, liquid or gas predict if a substance will be a solid, liquid or gas depends upon the pressure and temperature of the substance. depends upon the pressure and temperature of the substance. Triple Point Triple Point point where solid, liquid, and gas all exist – for water, 0 0 C. point where solid, liquid, and gas all exist – for water, 0 0 C. Example on page 381 Notice, that as you increase pressure, the boiling point of water increases- this is why a pressure cooker works. What about Denver, the “mile-high city?” End of Gases lecture, Chapters 10,11, problems following

22. Back Bires, 2007 Slide 22 In-chapter problems: Page 327, #5,7,8What is Pressure? Page 327, #5,7,8What is Pressure? Page 327, #11-14Pressure Units Page 327, #11-14Pressure Units Page 327, #17-19Pressure Conversions Page 327, #17-19Pressure Conversions Page 330, #20-24eBoyle’s Law Page 330, #20-24eBoyle’s Law Page 330, #25-27Charles’ Law Page 330, #25-27Charles’ Law Page 330, #31-35oCombined Law Page 330, #31-35oCombined Law Page 331, #39,40Dalton’s Law of Partial Pressures Page 331, #39,40Dalton’s Law of Partial Pressures Page 357, #9-13oAvogadro’s Molar Gasses Page 357, #9-13oAvogadro’s Molar Gasses Page 358, #17-20Ideal Gas Law Page 358, #17-20Ideal Gas Law Page 358, #23-29oIdeal Gas Law and Stoichiometry Page 358, #23-29oIdeal Gas Law and Stoichiometry Page 359, #39-42Graham’s Law of Gas Effusion Page 359, #39-42Graham’s Law of Gas Effusion End of Gases Unit, Chapters 10,11

23. Back Bires, 2007 Slide 23 CCSD Syllabus Objectives 11.1: Kinetic Molecular Theory 11.1: Kinetic Molecular Theory 11.2: Physical Properties of Gasses 11.2: Physical Properties of Gasses 11.3: STP 11.3: STP 11.4: Volume-Temp relationships 11.4: Volume-Temp relationships 11.5: Volume-Pressure relationships 11.5: Volume-Pressure relationships 11.6: Density-Volume-Pressure-Temperature 11.6: Density-Volume-Pressure-Temperature 11.10: Ideal Gas Law 11.10: Ideal Gas Law 11.11: Graham’s Law 11.11: Graham’s Law 11.12: Ideal Gas vs Real Gas 11.12: Ideal Gas vs Real Gas 12.3: Evaporation, Condensation, Sublimation 12.3: Evaporation, Condensation, Sublimation 21.1: Environmental Chemistry 21.1: Environmental Chemistry