Chapter 10 Gases Part 1 Ideal Gases Prepare for Recitation October 20th ALEKS Objective 8 due October 18th ANGEL Quiz 8 October 20th Lecture 22 October 12th Lecture 23 October 14th Lecture 24 October 17th Read Ch 10 1 10 9 Additional Preparation BLB 10 5 23 30 45 71 75 82 84 Packet 10 1 15 BLB 25 11 12 25 Are you a visual learner Intro chem okstate edu CH110 FA11 SAS 1 Chapter 10 Gases Part 1 Ideal Gases KEY QUESTIONS THE BIG PICTURE What does pressure mean What types of molecules can be found as gasses What state equation can we use to describe the properties of gasses Remember macroscopic properties come from microscopic origins How does the energy of a molecule in a gas compare with intermolecular forces How can we describe mixtures of gasses How do real gasses differ from ideal gasses By the end of Today s Lecture you should know Pressure and Boyle s Law Temperature and Charles Law Avogadro s Law Ideal Gas Law Density and Molecular Weight CH110 FA11 SAS 2 Exam 3 Concepts You Should Know Chapter 10 Gases What are the properties of ideal gases What is the partial pressure of a gas in a mixture How does kinetic molecular theory connect the microscopic properties of gases with observables How are real gases different from ideal gases Chapter 18 Atmospheric Chemistry What reactions occur in the atmosphere How do Chem 110 concepts show up in the atmosphere and environment Chapter 11 Intermolecular Forces What is heat capacity What are the properties of liquids How do you use phase diagrams Chapter 13 Aqueous Solutions What are electrolytes and how do we calculate the concentration of chemicals in solution What is meant by solubility and saturation What are colligative properties CH110 FA11 SAS 3 Gases The gas phase is characterized by Molecules that are moving and Intermolecular forces are Molecules with simple molecular formulas Which elements exist as gases under ordinary conditions Are metals ever found in gas molecules under ordinary condtions Spontaneous expansion to fill a container High compressibility The ability to form homogeneous mixtures more at the end of Chapter 10 CH110 FA11 SAS 4 Pressure Pressure Standard Atmospheric Pressure 1 atm 1 013 x105 Pa 1 atm 14 7 lb in2 1 atm 760 mm Hg torr Atmospheric pressure depends on Pressure is Caused by molecular collisions Dependent on density and temperature Earth s gravity affects the density of a gas and therefore affects its pressure CH110 FA11 SAS 5 Pressure and Altitude Pressure at a given altitude depends on the weight of the gas above it Altitude km 0 50 100 200 P atm 1 10 3 10 6 10 13 CH110 FA11 SAS Collision Frequency s 1 1010 107 103 1 6 Measuring Atmospheric Pressure What the Hell is a Torr Anyway The first measurement of pressure was made with a barometer by Torricelli in the 1600s Force from atmosphere must balance force from Hg in column Patm proportional to height of column Under standard conditions h 760 mm Note Height of column depends on what liquid is used 1 atm 10 m H20 CH110 FA11 SAS 7 Measuring Gas Pressure A Mercury Manometer can be used to measure the pressure of a gas in a closed container CH110 FA11 SAS 8 Pressure and Moles The state of a gas is described by P pressure V volume of container T temperature in Kelvin n moles of gas Avogadro s Law The volume of gas at constant temperature and pressure is proportional to the number of moles of gas present V n constant CH110 FA11 SAS 9 Pressure and Volume The state of a gas is described by P pressure V volume of container T temperature in Kelvin n moles of gas Boyle s Law At constant temperature and number of moles of gas the product of the pressure and volume is a constant PV constant 1 atm 1V 2 atm V CH110 FA11 SAS 4 atm V 10 Pressure and Temperature The state of a gas is described by P pressure V volume of container T temperature in Kelvin n moles of gas Charles Law At constant pressure and number of moles of gas the volume is proportional to the absolute temperature V T constant Absolute Temperature in Kelvin K K oC 273 15 CH110 FA11 SAS 11 The State of a Gas At constant T P V n constant V n At constant T n PV constant V V P 1 P At constant P n V T constant V T CH110 FA11 SAS 12 The Ideal Gas Law Avogadro Boyle Charles V constant fixed P T n PV constant fixed T n V constant fixed P n T All can be described with one relationship PV nRT gas constant Beware of R units are always important R 0 08206 L atm mol 1K 1 R 8 314 J mol 1K 1 CH110 FA11 SAS 13 Standard Temperature and Pressure The Ideal Gas Law is a State Function PV nRT STP Standard Temperature and Pressure is frequently encountered and is defined as T 0oC 273 K P 1 atm Practice Problem What is the volume V occupied by 1 00 mole of gas at exactly 0oC and 1 atm CH110 FA11 SAS 14 Changes in P V and T Given initial conditions Pi Vi Ti and final conditions for two quantities Find the value for the 3rd final value Pi Vi nR Ti Pf Vf Pi Vi Ti Pf Vf Tf nR Tf CH110 FA11 SAS 15 Practice Problem The gas in a 750 mL vessel at 105 atm and 27 oC is expanded into a vessel of 54 5 L and 10 oC What is the final P A B C D E 0 0051 atm 0 014 atm 0 77 atm 1 3 atm 73 atm CH110 FA11 SAS 16 Density and Molecular Weight of Gases PV nRT Number of moles in a gas g n moles m m mass M M molar mass g mol Therefore PV m RT M rearrange MP m RT V Density d is d m V Volume in L density molar mass CH110 FA11 SAS 17 Helium Balloons are Boring to Blow Up but now we know why they float What is the density of He gas in g L at 21oC and 752 torr Under these conditions the density of air is 1 188 g L The mass difference between 1L of He and 1L of air is This is the buoyant lifting force of He per L CH110 FA11 SAS 18 Practice Problems Which one of the following samples contains the largest number of molecules 1 1 0 L of H2 g at STP 2 1 0 L of N2 g at 0oC and 800 mm Hg 3 1 0 L of CO2 g at 0oC and 600 mm Hg Which one of the following gas samples contains the highest density 1 1 mole of He g in a 10 L flask at STP 2 1 mole of N2 g in a 10 L flask at STP 3 1 mole of CO2 g in …
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