Chapter 11 - Gases. Lesson 1 – Gases and Pressure. Essential Questions: What is pressure?. Kinetic Molecular Theory. Particles in an ideal gas… have no volume. have elastic collisions. are in constant, random, straight-line motion. don’t attract or repel each other.
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Lesson 1 – Gases and Pressure • Essential Questions: • What is pressure?
Kinetic Molecular Theory • Particles in an ideal gas… • have no volume. • have elastic collisions. • are in constant, random, straight-line motion. • don’t attract or repel each other. • have an avg. KE directly related to Kelvin temperature.
Real Gases • Particles in a REAL gas… • have their own volume • attract each other • Gas behavior is most ideal… • at low pressures • at high temperatures • in nonpolar atoms/molecules
Characteristics of Gases • Gases expand to fill any container. • random motion, no attraction • Gases are fluids (like liquids). • no attraction • Gases have very low densities. • no volume = lots of empty space
Characteristics of Gases • Gases can be compressed. • no volume = lots of empty space • Gases undergo diffusion & effusion. • random motion
Temperature K = ºC + 273 ºF -459 32 212 ºC -273 0 100 K 0 273 373 • Always use absolute temperature (Kelvin) when working with gases.
Pressure Which shoes create the most pressure?
Pressure Aneroid Barometer Mercury Barometer • Barometer • measures atmospheric pressure
Pressure U-tube Manometer Bourdon-tube gauge • Manometer • measures contained gas pressure
Pressure • KEY UNITS AT SEA LEVEL 101.325 kPa (kilopascal) 1 atm 760 mm Hg 760 torr 14.7 psi
STP Standard Temperature & Pressure 0°C273 K 1 atm101.325 kPa -OR- STP
Dalton’s Law Ptotal = P1 + P2 + ... • The total pressure of a mixture of gases equals the sum of the partial pressures of the individual gases. When a H2 gas is collected by water displacement, the gas in the collection bottle is actually a mixture of H2 and water vapor.
Dalton’s Law • Hydrogen gas is collected over water at 22.5°C. Find the pressure of the dry gas if the atmospheric pressure is 94.4 kPa. The total pressure in the collection bottle is equal to atmospheric pressure and is a mixture of H2 and water vapor. GIVEN: PH2 = ? Ptotal = 94.4 kPa PH2O = 2.72 kPa WORK: Ptotal = PH2 + PH2O 94.4 kPa = PH2 + 2.72 kPa PH2 = 91.7 kPa Look up water-vapor pressure on p.899 for 22.5°C.
Dalton’s Law • A gas is collected over water at a temp of 35.0°C when the barometric pressure is 742.0 torr. What is the partial pressure of the dry gas? The total pressure in the collection bottle is equal to barometric pressure and is a mixture of the “gas” and water vapor. GIVEN: Pgas = ? Ptotal = 742.0 torr PH2O = 42.2 torr WORK: Ptotal = Pgas + PH2O 742.0 torr = PH2 + 42.2 torr Pgas = 699.8 torr Look up water-vapor pressure on p.899 for 35.0°C.
Lesson 2 – The Gas Laws • Essential Questoins: • How do Boyle’s law, Charles’s law, Gay-Lussac’s law, and the combined gas law describe the behavior of gases?
A. Boyle’s Law P V PV = k
A. Boyle’s Law P V • The pressure and volume of a gas are inversely related • at constant mass & temp P1V1=P2V2
A. Boyle’s Law http://www.marymount.k12.ny.us/marynet/06stwbwrk/06gaslaws.html
B. Charles’ Law V T
B. Charles’ Law V T • The volume and absolute temperature (K) of a gas are directly related • at constant mass & pressure
B. Charles’ Law http://www.marymount.k12.ny.us/marynet/06stwbwrk/06gaslaws.html
C. Gay-Lussac’s Law P T • The pressure and absolute temperature (K) of a gas are directly related • at constant mass & volume http://www.marymount.k12.ny.us/marynet/06stwbwrk/06gaslaws.html
D. Combined Gas Law • Boyle’s law, Charles’s law, and Gay-Lussac’s law are combined • Used when a gas undergoes changes in pressure, temperature, and volume all at once • Remember, temperature must be in Kelvin
D. Combined Gas Law P1V1 T1 P2V2 T2 = P1V1T2 =P2V2T1
E. Gas Law Problems • A gas occupies 473 cm3 at 36°C. Find its volume at 94°C. CHARLES’ LAW GIVEN: V1 = 473 cm3 T1 = 36°C = 309K V2 = ? T2 = 94°C = 367K T V WORK: P1V1T2 = P2V2T1 (473 cm3)(367 K)=V2(309 K) V2 = 562 cm3
E. Gas Law Problems • A gas occupies 100. mL at 150. kPa. Find its volume at 200. kPa. BOYLE’S LAW GIVEN: V1 = 100. mL P1 = 150. kPa V2 = ? P2 = 200. kPa P V WORK: P1V1T2 = P2V2T1 (150.kPa)(100.mL)=(200.kPa)V2 V2 = 75.0 mL
E. Gas Law Problems • A gas occupies 7.84 cm3 at 71.8 kPa & 25°C. Find its volume at STP. COMBINED GAS LAW P T V GIVEN: V1=7.84 cm3 P1=71.8 kPa T1=25°C = 298 K V2=? P2=101.325 kPa T2=273 K WORK: P1V1T2 = P2V2T1 (71.8 kPa)(7.84 cm3)(273 K) =(101.325 kPa)V2 (298 K) V2 = 5.09 cm3
E. Gas Law Problems • A gas’ pressure is 765 torr at 23°C. At what temperature will the pressure be 560. torr? GAY-LUSSAC’S LAW GIVEN: P1 = 765 torr T1 = 23°C = 296K P2 = 560. torr T2 = ? P T WORK: P1V1T2 = P2V2T1 (765 torr)T2 = (560. torr)(309K) T2 = 226 K = -47°C
Lesson 3 – Gas Volume and the Ideal Gas Law • Essential Questions: • What is the relationship between the volumes of gases that react with each other? • How does the ideal gas law unify all the other laws to describe the behavior of gases?
Avogadro’s Principle V n • Equal volumes of gases contain equal numbers of moles • at constant temp & pressure • true for any gas
Ideal Gas Law = k V n Merge the Combined Gas Law with Avogadro’s Principle: PV T PV nT = R UNIVERSAL GAS CONSTANT R=0.0821 Latm/molK R=8.315 dm3kPa/molK You don’t need to memorize these values!
Ideal Gas Law PV=nRT UNIVERSAL GAS CONSTANT R=0.0821 Latm/molK R=8.315 LkPa/molK You don’t need to memorize these values!
Ideal Gas Law Problems • Calculate the pressure in atmospheres of 0.412 mol of He at 16°C & occupying 3.25 L. GIVEN: P = ? atm n = 0.412 mol T = 16°C = 289 K V = 3.25 L R = 0.0821Latm/molK WORK: PV = nRT P(3.25)=(0.412)(0.0821)(289) L mol Latm/molK K P = 3.01 atm
Ideal Gas Law Problems WORK: 85 g 1 mol = 2.7 mol 32.00 g • Find the volume of 85 g of O2 at 25°C and 104.5 kPa. GIVEN: V=? n=85 g T=25°C = 298 K P=104.5 kPa R=8.315dm3kPa/molK = 2.7 mol PV = nRT (104.5)V=(2.7) (8.315) (298) kPa mol dm3kPa/molKK V = 64 dm3
Ideal Gas Law Problems • Practice problems on page 385. • Page 392 #49-52 • Ideal Gas Law Worksheet
Graham’s Law • Diffusion • Spreading of gas molecules throughout a container until evenly distributed. • Effusion • Passing of gas molecules through a tiny opening in a container
Graham’s Law • Speed of diffusion/effusion • Kinetic energy is determined by the temperature of the gas. • At the same temp & KE, heavier molecules move more slowly. • Larger m smaller v KE = ½mv2
Lesson 4 – Global Warming and Greenhouse Gases • How does the release of greenhouse gases affect the carbon cycle? • What are the major sources of air pollution and their effects on the environment? • Using the properties of gases, how can air pollution be controlled?
Most of the atmosphere’s mass and all of its weather are within 10 to 15 km of the Earth’s surface. (troposphere) Ancient air trapped in glacial ice has about the same makeup as the current atmosphere. http://www.whfreeman.com/Chemcom/ For interactive atmospheric air. Structure of the Atmosphere
Carbon Cycle • The concentration of carbon in living matter is 18%, while it is 0.19% in nonliving matter. For life to continue, this carbon must be recycled. • Carbon in living matter vs. carbon in nonliving matter. • 71% of Earth’s carbon is found in the oceans.
Rising Levels of Carbon Dioxide • Without humans, CO2 levels would remain virtually unchanged. • Limestone CaCO3 is decomposed to CaO and CO2 is released. • Clearing forests takes away plants that would remove CO2 from the atmosphere. • Burning fossil fuels releases CO2 • Coal C + O2 → CO2 • Gasoline 2C8H18 + 25O2→16CO2 + 18H2O
Greenhouse Effect • CO2 in the atmosphere retards the radiation of heat from the earth back into space – “greenhouse effect” • If enough CO2 is added than can be removed by natural processes, then the temperature of the earth will increase. • Other greenhouse gases include nitrous oxide, chlorofluocarbons (CFCs), and methane.
Global Warming • Ten of the warmest years since 1880 have occurred since 1983. • Most climate specialists think earth’s temperature will increase 1.0° to 3.5°C in the next 100 years.
Projected Effects of Global Warming • Oceans will rise 5cm each decade over the next century due to melting of ice caps and expansion of ocean water with increased temperature. • Flooding in major cities due to increased ocean levels. • Warmer temperature results in increases in extreme weather events. • Warmer atmosphere can hold more moisture, making big storms more likely. • Shorter winters with more blizzards • Kyoto Protocol • Sets ambitious goals for reducing greenhouse gas emissions. • For industrialized nations, involves developing energy efficient technologies, relying more heavily on renewable enrgy, and using alternative processes that don’t produce carbon dioxide. • Example – use of biofuels possibly reduces carbon emissions.
Kyoto Protocol Dark green = countries that have signed and ratified the treaty Yellow = signed by not yet ratified Grey = not decided yet Red = no intention of ratifying
Carbon dioxide Nitrogen oxides Carbon monoxide Sulfur dioxide Particulate Matter Lead Ozone Major Air Contaminants
Smog in the Environment • Smog is a combination of smoke and fog • Caused by the interaction of air contaminants with meteorological conditions. • Smog can cause severe respiratory distress and even has been listed as the cause for 4000 deaths in London in 1952. • Photochemical smog is the smog found over cities that is due to the reaction of chemicals in the air with light. • Major causes of this are nitrogen oxides, ozone, and hydrocarbons.