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by: Miss Tyrell Rippin


Miss Tyrell Rippin
GPA 3.6


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Class Notes
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This 119 page Class Notes was uploaded by Miss Tyrell Rippin on Tuesday October 20, 2015. The Class Notes belongs to CHEM200 at San Diego State University taught by M.Bennett in Fall. Since its upload, it has received 190 views. For similar materials see /class/225325/chem200-san-diego-state-university in Chemistry at San Diego State University.




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Date Created: 10/20/15
Chapter 6 Thermmhemistry Energy FQW and Chemical Change 11 12 Thermochemistry Energy Flow and Chemical Change 61 Forms of Energy and Their Interconversion 62 Enthalpy Heats of Reaction and Chemical Change 63 Calorimetry Laboratory Measurement of Heats of Reaction 64 Stoichiometry of Thermochemical Equations 65 Hess s Law of Heat Summation 66 Standard Heats of Reaction AHo rxn Learning Outcomes Chapter 6 Students should Understand the distinction between a system and its surroundings Understand why a system and the surroundings must be de ned in order to observe and measure changes in energy Be able to determine the change in internal energy AE given the amounts of energy transferred as work w and heat q know the sign conventions for work and heat Understand the meaning of energy conservation Be able to de ne the thermodynamic variable enthalpy 1D know how enthalpy differs from internal energy and be aware of the importance of enthalpy changes AID in chemistry 13 Learning Outcomes Chapter 6 Students should Know the difference between endothermic and exothermic chemical reactions and be able to identify endothermic or exothermic reactions or processes Understand the relationship between AH rXII and amount of substance Be able to determine the enthalpy change for any amount of reactant or product given a balanced thermochemical equation Know the sign of the energy change associated with making or breaking a chemical bond and understand the importance of bond energies in determining the enthalpy change for a reaction Know the standard states of the common elements from handout 1n syllabus p 17 1 4 Learning Outcomes Chapter 6 Students should Be able to identify or write the formation equation for a given compound Be able to use Hess s Law or standard heats of formation AHOf to determine the enthalpy change for a chemical reactlon Know the difference between heat capacity and specific heat capacity be able to convert a speci c heat capacity into a heat capacity and vice versa Know how to use heat capacity and speci c heat capacity to determine the heat released or absorbed for a process given a temperature change and vice versa Understand how calorimeters are used to experimentally measure heat transfers be able to calculate heats of reactlon given information about a calorimetry experiment 15 Thermodynamics is the study of heat and its transformations Thermochemistry is a branch of thermodynamics that deals with the heat involved with chemical and physical changes Fundamental premise When energy is transferred from one object to another it appears as work andor as heat For our work we must define a system to study everything else then becomes the surroundings The system is composed of particles with their own internal energies E or U Therefore the system has an internal energy When a change occurs the internal energy changes 16 Units of Energy joule J 1 kgm2s2 calorie cal energy needed to raise temperature OH 9 of water by 1 C 1 cal 4184 J kilojoule kJ 1000 J kilocaloriekcal 1000 cal 1Calorie 17 Some interesting quantities of energy 102 1 J 102 J 1015 7 WM 1012 109 106d 10M 10 103 J 10 6J 10quot9 J 1042 J 10 5J WM 104 J Dain solar energy Q 7 falling on Earth Energy of a strong arthquake Daily electrical J ouiput of Hoover Dam 1000 tons of coal burned 1 ton of TNT exploded 1 kilowatthourof if electrical energy T Heat released from combustion of1 mol glucose e 1 calorie 41184 J ow Heal absorbed during division of one bacterial cell Energy from fission of one 235U atom I V 316 53 w Average kinetic energy of a molecule in air at 300 K Types of Energy Kinetic Energy energy associated with motion Potential Energy energy associated with position Internal Energy E sum of kinetic and potential energy for a system 19 Changes in Energy AE surroundings energy in AE gt0 sys system energy out AEsys lt 0 AE system AEs AEuniverse O urroundings the system 111 Changes in Energy AE L E nal A Energy E Energy E Efinal Einitial A E of system decreases B E of system Increases AE is a state function State Functions State functions depend only on initial and final states of the system and not on how the change was accomplished Energy E pressure P volume V and temperature T are all state func ons State Functions Altitude vs Distance Distance d depends on path Altitude A path independent AA Af A AA 5280 ft Methods of Transferring Energy heat q thermal energy transferred as a result of a difference in temperature work W energy transferred when an object is moved by a force AEq w q gt 0 system gains heat q lt 0 system loses heat Sign Conventions for q and w w gt 0 work done on system w lt 0 work done by system q W AE depends on sizes of q and w depends on sizes of q and w Heat Transfers and Temperature Tsys gt Tsurr Tsys Tsun Ermal Energy E Energy E Elmua A E Ios as heal B E gained as heat 117 A Energy E 118 system losing energy as work only Einitial Work w done on surroundings w lt O Efinal Initial state Surroundings w PAV Final state Pressure volume work Example What is the change in internal energy in J of a system that releases 675 J of thermal energy to its surroundings and has 525 cal of work done on it 120 Enthalpy H the sum of the internal energy and the product of the pressure and volume for a system HEPV the change in enthalpy AH is equal to the heat transfer for a system at constant pressure qp AH AE PAV w PA AH AE W qAE W AH qID 121 Heat of Reaction AH I39Xh the enthalpy change associated with a chemical reaction AH H l Xl l H products reactants the sign of Aern indicates whether heat is released or absorbed during the reaction 122 Endothermic vs Exothermic l ZHMJ 020 M Hem given off by system 2H 5 Hem absomed by system 2Hg0 Exomermlc Endomennic Exothermic Reaction AH lt O H2g F2g gt 2 HFg AH 546 kJ heat is released during the reaction heat is a product of the reaction Endothermic Reaction AH gt O N2g 029 gt 2 NOg AH181 kJ heat is absorbed during the reaction heat is a reactant in the reaction 124 An Enthalpy Diagram for a Chemical Reaction N2g 029 gt 2 NOg AH181 kJ 2 NOg F mal AHth 181 kJ Enthalpy lD h59 39 Cbg m al 125 Thermochemical Equations H2g F2g gt 2 HFg AH 546 kJ 2 HFg gt H2g F2g AH 546 kJ 12 H2g 12 F2g gt HFg AH 273 kJ sign of Aern depends on reaction direction magnitude of Aern depends on amount 126 Thermochemical Equation Guidelines Always specify state of reactants and products When multiplying an equation by a factor n multiply the AH value by same factor Reversing an equation changes the sign but not the magnitude of the AH 127 What is the enthalpy change associated with the formation of 340 moles of HF H2g F2Q 2 HFQ Aern 546 M 546 kJ 340 moles HF x 928 kJ 2 moles HF 546 kJ 546 kJ 546 kJ 1 mole H2 1 mole F2 2 moles HF 128 Utmmpc vmt of Enthalpy Change i 7 J 395 171 Miquot 1 Iquot quotquot U L H77 7 mammary C4H1ol 13202g gt 4C02g 5H20g heat of formation AHf Ks 123r21 gtKBrs 39E a g 39 3 rr 7 gt 3 r 39 2V 39 ngrl 4 I w 9 LA 44 th NaCs NaCl heat of vaporization AHvap C6H6l 39 CsHsg 129 Where does AH come from I39Xh differences in bond energies between the reactants and products in the reaction H2g gt 2 Hg AH 432 kJ breaking bonds is always endothermic 2 Hg gt H2g AH 432 kJ making bonds is always exothermic 130 Bonds Energies and AH I39Xh H2g F2g gt 2 HFg AH 546 kJ more bond energy N2g 029 gt 2 NOg AH 180 kJ f more bond energy 131 TwoCarbon Compounds OneCarbon Compounds Ethane CZH6 Ethanol CZHsO Methane CH4 Methanol CH4O St t I T T T39 739 739 T F ruc ulra H C C H H c c o H H li H H C O H ormu as 39139 39139 H H H 39139 Sum of 00 and 0H Bonds 7 6 4 3 Sum of C0 and 0H Bonds 0 2 O 2 AHcombkJmol 1 560 1 367 890 727 AHcombkJg 5188 2967 555 227 132 Heats of Combustion of Some Fats and Carbohydrates Substance AHcombleg Fats vegetable oil 370 margarine 301 butter 300 Carbohydrates table sugar sucrose 162 brown rice 149 maple syrup 104 133 Hess s Law The enthalpy Change of an overall process is the sum of the enthalpy Changes of its individual steps AH AHStep1 AHStepZ AHStep3 overall 1 34 Calculating unknown AH using Hess s Law 1 Identify target equation whose AH is unknown note of moles of reactants and products 2 Manipulate equations for which AH known Change sign of AH when you reverse an equation Multiply of moles and AH by the same factor 3 Add up equations to get target equation Everything else much cancel Add up AHs to obtain unknown AH 135 136 Enthalpy lD Hess s Law Diagram 2 NOg 029 w N2g 2 029 AH2 1142 kJ AH1 1806 kJ 2 NO2g AH3 664 kJ Formation Equations and Heats of Formation AH f Formation Equation An equation in which 1 mole of a substance is formed from its elements in their standard states 12 H2g 12 F2g gt HFg AHofHFg Heat of Formation AH f The enthalpy change associated with the formation reaction for a substance 137 Standard States of the Elements Most stable form of an element at 1 atm and 25 C 298 K Are the reactants in formation equations of substances An element s heat of formation AH f in its standard states is zero 138 Using Heats of Formation to Find Heats of Reaction Elements o Decom position u39gt I quotO D I UoilEUJJOj Hinitial AH r xn AH rxn ZAH fproducts ZAH freactants Enthalpy H 139 Summary of the relationship between amount mol of substance and the heat kJ transferred during a reaction Copyright The McGrawHill Companies Inc Permission required for reproduction or display molar ratio f b I d r r qu2 e 4 OUNTE AernltkJm 39gt compoun w 1 40 Summary of the relationship between amount mol of substance and the heat kJ transferred during a reaction AMOUNT mol of compound B molar ratio from balanced equation III III I II II I haii i Aern kJmol 141 ESWJQEMJ H ef brmation at 25 C298K Formula AH fkJmol Formula AH fkJmol Formula AH fkJmol calcium C2g 0 Silver Cas O 92 3 Ags O Caos 6351 CW 39 AgCs 4270 CaCO3s 42059 hydrogen carbon g 21 sodium Cgraphite O 2g NaS 0 Cdiamond 19 nitrogen Nag 1078 C0g 4105 N2g o NaCIs 4114 C02 393935 NH35 39459 sulfur CH4g 749 N0g 903 88rhombic o CHsoHU 392386 oxygen 88monoclinic 2 HCNg 135 so g 2968 CS 1 879 02g 0 2 S 03g 143 SO3g 3960 Chlorine H20g 2418 Cg 1210 H20l 2858 1 42 The general process for determining AH rxn from AH f values Elements uoueuuod Hiniual AHxn Enlhalpy H o u D Hfinal AHan EmAH products EnAHKreactants What is the formation reaction of aluminum chloride A 12A2g 32cI2g gt AICI3s B 2As 3029 gt 2AICI3S As 32cI2g gt AICI3s D As 3Clg gt AICI3s 1 44 Thermochemistry Energy Flow and Chemical Change 63 Calorimetry Laboratory Measurement of Heats of Reaction 145 Measuring Heat Changes surroundings com system heat hOt can measure heat transfers by measuring the change in temperature A7 for the surroundings qsys qsurr 146 Converting Temperature To Heat Heat Capacity C amount of heat needed to raise the temperature of an object by 1 K heat capacity qAT units of JK Specific Heat Capacity 0 amount of heat needed to raise the temperature of 1 gram of substance by 1 K c qmass x AT units of JgK 147 Which would require more heat to raise the temperature by 1 C a cup of water a swimming pool the swimming pool it has the greater heat capacity more mass 148 Which would require more heat to raise the temperature by 1 C 10 g of water 10 g of gold cwater 418 JgK cAu 0129 JgK the 10 g of water because water has the greater speci c heat capacity 149 Some Specific Heat Capacities Substance Specific Heat Substance Specific Heat Capacity JgK Capacity JgK Elements Materials aluminum AI 0900 wood 176 graphiteC 0711 cement 088 iron Fe 0450 glass 084 copper Cu 0387 granite 079 gold Au 0129 steel 045 Compounds water H20l 4184 ethyl alcohol C2H50Hl 246 ethylene glycol CHZOH2I 242 carbon tetrachloride CCI4l 0864 150 Coffee Cup Calorimeter Thermometer qsys qsurr Styrofoam cups qrer qoa insulation Water surroundings exothermic reaction AT endothermic reacton AT e Sample system A Bomb Calorimeter Electrical Motorized source stirrer Thermometer System combustible substance and compressed oxygen Cutaway of Cutaway of insulated jacket steel bomb Water bath Ignition co39l Heat being transferred 152 Question 633 Calculate q when 120 g of water is heated from 20 C to 100 C 153 Question 635 A 2959 aluminum engine part at an initial temperature of 300 C absorbs 850 kJ of heat What is the final temperature of the part c of AI 0900 JgK 154 Question 637 Two iron bolts of equal mass one at 100 C the other at 55 C are placed in an insulated container Assuming the heat capacity of the container is negligible what is the final temperature inside the container 0 of iron 0450 JgK 155 Question 677 Copperl oxide can be oxidized to copperl oxide Cu20s 12O2g gt ZCuOs Aern 1460 kJ Given that AHfo of Cu20s 4686 kJmol what is the AHfo of CuOs 156 11 General Chemistry CHEM 200202 Prof Miriam Bennett September 4 2009 12 Announcements In lab assignment due next WTh Online HW assigned by next W Demo on Wednesday Clickers next Friday Bring calculators only nonprogrammable accepted for exams Casio fx3OO MS sold at bookstore Chemistry and You 1 4 The Language of Chemistry Elements the letters of chemistry Chemical Formulas the words of chemistry Chemical Equations the sentences of chemistry Naming Acids Binary acids form when gaseous compounds dissolve in water hydro anion nonmetal root ic the word acid When gaseous hydrogen chlorideHCl dissolves in water hydro chlor ic acid gt hydrochloric acid Oxoacids Anion quotate suffix becomes an ic suffix in the acid Anion quotite suffix becomes an quotous suffix in the acid The oxoanion prefixes hypo and per are retained BrO4 is perbromate and HBrO4 is perbromic acid IOZ39 is iodite and HIO2 is iodous acid 16 CHsCOZH H2804 HNO3 HClaq HCKQ Common Acids acetic acid sulfuric acid nitric acid hydrochloric acid hydrogen chloride What are the names of each of the following compounds A N205 B PBr3 C NaZSO4 D CuCI2 Some Common Chemical Substances water salt baking soda sugar Splenda 18 H20 NaCI NaHCO3 C1222C11 C12H1903C8 TumsTM vinegar CloroxTM hydrogen peroxide caffeine CaCO3 CH3002H NaCIO H202 C8H10N4C2 19 Chapter 3 of Formulas and Equations The Moe molemol the amount of a substance that contains the same number of entities as there are atoms in exactly 12 g of carbon12 This amount is 6022 x 1023 The number is called Avogadro s number and is abbreviated as N mo39e 1 mOI Contains 6022 itquot ties to four significant figure 1 10 One mole of common substances Summary of Mass Terminology Term Isotopic mass Atomic mass also called atomic weight Molecular or formula mass also called molecular weight Molar mass M also called gram molecular weight 112 Definition Mass of an isotope of an element Average of the masses of the naturally occurring isotopes of an element weighted according to their abundance Sum of the atomic masses of the atoms or ions in a molecule or formula unit Mass of 1 mole of chemical entities atoms ions molecules formula units Unit amu amu amu gmol Information Contained in the Chemical Formula of Glucose C6H1206 M 18016 gmol Carbon C Hydrogen H Oxygen 0 Atomsmolecule 6 atoms 12 atoms 6 atoms of compound Moles of atoms 6 mol of 12 mol of 6 mol of m0o 01 compound atoms atoms atoms AtomSm0e Of 66022 X 1023 126022 X 1023 66022 X 1023 compound atoms atoms atoms MaSSm0eCUe 61201 amu 121008 amu 61600 amu 01 compound 7206 amu 1210 amu 9600 amu Massmole of 7206 g 1210 g 9600 9 compound 113 MASS g of element f Avogadro39s number atomsmol ATOMS 0 element Summary of the massmolenumber relationships for elements Interconverting Moles Mass and Number of Chemical Entities no of grams Mass 9 no of moles x 1 mol 1 mol No of moles mass 9 x no of grams 6022x1023 entities No of entities no of moles x 1 mol 1 mol No of moles no of entities x 6022x1023 entities Calculating the Number of Moles and Atoms in a Given Mass of Element Problem Tungsten W is the element used as the lament in light bulbs and has the highest melting point of any element 368000 How many moles of tungsten and atoms of the element are contained in a 350 mg sample of the metal Plan Convert mass into moles by dividing the mass by the atomic weight of the metal then calculate the number of atoms by multiplying by Avogadro s number Summary of the massmolenumber relationships for compounds Copyright The McGraw Hill Companies Inc Permission required for reproduction or display MASS g of compound AL gmol chemical formula in compound I f Avogadro39s number moleculesmoi MOLECULES or formula units of compound Problem Molar Mass Calculate the molar mass of each of the following compounds Barium hydroxide Chromiumll oxide Learning Outcomes Chapter 3 Students should Understand the concept of the mole and why it is useful in chemistry Know the relationships between moles molecules mass and chemical formuas be able to convert molecular and mass quantities into molar quantities Know how to calculate the molar mass of a compound Knowthat more than one substance can have the same empirical formula and the same molecular formula isomers Be able to write balance and manipulate chemical equanons Knowhow to use stoichiometric ratios from a balanced equation to determine amounts of reactants consumed and products formed In a reaction Learning Outcomes Chapter 3 Students should Understand why one reactant limits the yield of product and how to determine the limiting reactant and amount of product formed for a reaction given the appropriate information Be aware of the practical importance of chemical yield in stoichiometry Know the difference between the theoretical actual and percent yields for a chemical reaction Be able to use chemical yield information for a reaction in stoichiometric calculations Know how to combine chemical equations to give an overall net equation for a multistep reaction 120 Learning Outcomes Chapter 3 Students should Be able to identify intermediates in a chemical reaction sequence Be able to use an overall equation to perform stoichiometric calculations for a multistep chemical reaction Know what a solution is and be familiar with the terms used to describe the concentration of a solution solute solvent concentrated dilute Know the definition of molarity Be able to use molarity to determine the amount of solute present in solution for use in stiochiometry calculations 121 11 Chapter 5 w 3536 KineticMolecular Theory 12 Gases and the Kinetic Molecular Theory 51 An Overview of the Physical States of Matter 52 Gas Pressure and Its Measurement 53 The Gas Laws and Their Experimental Foundations 54 Further Applications of the Ideal Gas Law 55 The Ideal Gas Law and Reaction Stoichiometry 56 The KineticMolecular Theory A Model for Gas Behavior 57 Real Gases Deviations from Ideal Behavior Learning Outcomes Chapter 5 Students should Be able to qualitatively describe the physical behavior of gases and how this behavior differs from liquids and solids Understand what is meant by gas pressure and be familiar with how it is measured Understand that the physical behavior of ideal gases depends only on pressure P volume V temperature 7 and amount n Be able to interconvert among the common units of pressure atm mm Hg torr pa psi When given the appropriate conversion factors 13 Learning Outcomes Chapter 5 Students should Be able to use the ideal gas law to determine the pressure volume temperature or amount of an ideal gas given the other variables Be able to qualitatively describe or quantitatively determine the effect of changing the pressure volume temperature or amount of an ideal gas Be to determine the density or molar mass of a gas using the ideal gas law Be able to use the ideal gas law to find amounts of gas in a stoichiometric calculation Know Dalton s Law of Partial Pressures and how it applies to a mixture of ideal gases Learning Outcomes Chapter 5 Students should Be able to calculate the partial pressure of a gas using either the ideal gas law or the mole fraction of the gas in a gas mixture and vice versa Be able to apply stoichiometry and gas laws to calculate amounts of reactants and products or a balanced chemical reaction when given the appropriate information Know the postulates of the kineticmolecular theory and how they are applied to explain the origin of pressure and the gas laws Know and be able to explain the relations among molecular speed average kinetic energy and temperature The meanings of effusion and diffusion and how their rates are related to molar mass 15 The Three States of Matter A Gas Molecules are E Liquid Molecules are C Solid Molecules are far apart and iill the close together but move tightly packed In a regular available space relative to each other array and move very little relative to each other Gases Are Strange 17 Gas volume varies dramatically with changes in pressure and temperature Gases have low viscosities flow freely Gases have low densities mostly empty Gases are miscible mix perfectly in all proportions The physical behavior of gases does not depend on chemical identity ideally The Ideal Gas Law The physical behavior of an ideal gas can be completely described by only four variables Pressure P Volume V Temperature T Amount moles n PV nRT R Universal Gas Constant 008206 LatmmolK 18 Changing Conditions The Ideal Gas Law can also account for the response of a gas to a change in conditions P1V1 P2 v2 quot1 T1 quot2 T2 Initial conditions subscript 1 Final conditions subscript 2 19 Measuring Pressure Atmospheric pressure Common Units of Pressure Unit Atmospheric Pressure Scientific Field pascalPa kilopascalkPa atmosphereatm millimeters of mercuryHg torr pounds per square inch psi or Ibin2 bar 101325 X 105 Pa 101325 kPa 1 atm 760 mmHg 760 torr 147 Ibin2 101325 bar SI unit physics chemistry chemistry chemistry medicine biology chemistry engineering meteorology chemistry physics The Kinetic Molecular Theory of Gases A gas consists of a large collection of individual particles that are very small no volume Gas particles are in constant random straight line motion except for collisions Collisions between particles are elastic their total kinetic energy E3 is constant Between collisions the gas particles do not influence each other in any way act independently A Model of a Gas Sample empty space very small particles gas pressure from collnsnons How Fast Do the Particles Of A Gas Move Very fast Speeds increase with temperature Ek 3I2RINAT Temperature is a measure of molecular motion 114 Relative number of molecules with speed u Most probable speed at 1273 K 2000 3000 u ms Understanding the Ideal Gas Law PV nRT Initially discovered through observations of gas behavior changing volumes Macroscopic behavior of gases explained by the Kinetic Molecular Theory Boyle s Law The volume of an ideal gas is inversely proportional to the external pressure at fixed Tand n P1V1 sz2 191711 492752 V2 P1P2V1 The PressureNolume Relationship va V 1P vs V 320 15 g 15 CD 10 E 10 D 5 7quot 5 j l I I l i I 1000 2000 3000 00095 010010 00015 Ptotal 10 T Pintal A Molecular View of Boyle s Law p ext Increased T n constant 0 00 1 L volume decreases more frequent collisions force over a smaller surface area Charles s Law The volume of an ideal gas is directly proportional to the temperature of the gas at fixed P and n P1V1 P2V2 V1 V2 quot2T2 T1 T2 quot1 T1 V2 T2T1V1 A Molecular View of Charles s Law Pgas Palm Higher Tincreases Vincreases umquot collision lrequency P Pgas gt Palm gas 39 am Thermometer Glass tube Mercury u p1 9 H Trapped air I sample llri Jlnl A lce water bath 0 C 273 K B Boiling water bath 100 C 373 K Charles s Law 121 The relationship between Volume L the volume and temperature of a gas 80 20 n 004 mol P 1 atm 10 I I I ll 1 r n004mo 3 v P4atm l l l l l 273 200 100 O 100 200 300 400 500 C 0 73 173 273 373 473 573 673 773 K Temperature Charles s Law and Absolute Zero Tvs V Celsius Scale arbitrary zero point freezing point of water Zero volume 27315 C Volume L Kelvin Scale K absolute 1 temperature scale 0 K is the lowest possible temperature 0 K molecular motion stops 39200 0 20 40 73 273 473 673 27315 3C Temperature CK 0 K absolute zero 122 Avogadro s Law The volume of an ideal gas is directly proportional to the amount of gas at fixed P and T P1 V1 P2 V2 V1 V2 quot1 T1 quot2T2 quot1 quot2 V2 quot2quot1V1 At fixed P and T equal volumes of an ideal gas contain an equal number of particles 123 A Molecular View of Avogadro s Law F gas Patm More molecules Vincreases um increase col isions Pgas Pa m Pgas gt Palm 124 Avogadro s Law Revisited Why do equal numbers of particles of an ideal gas occupy equal volumes at constant temperature and pressure He 4 gmol Ar 40 gmol 39 o o o 39 o o ll Ek 32RNAT more force per collision 1k 12m52 m mass u speed 125 Mass versus Speed w 2 quotD g i 02 32 E g N2 23 Q E 3 H2018 g m He 4 C 3 g a H2 2 5 0 cc Molecular speed at a given T Gas particles with lower masses have higher speeds Rootmeansquared speed urms 3RTmoar mass 2 1 26 An experiment to study the relationship between the volume and amount of a gas P1 V1 T15 quot1 P2 V2 T25 quot2 P1 P2 Patm T1 T2 constant RM FSV2 V2 quotzn1V1 quot17 quot275 127 1 28 Standard Molar Volume O D 224L Q O I o particles 6022x1023 gas 6022x1023 6022x1023 THE IDEAL GAS LAW PV 1atmx22414L 00821atmL R nT 1mo X 273 15K moK IDEAL GAS LAW nRT PV nRT or V xed 17 and T xed 17 and P xed P and T Boyle s Law Charles s Law Avogadro s Law V conStant V constant X T V conStant X n P 129 If a 300 L balloon filled with gas at 2925 K has a pressure of 12 atm then how many moles of gas are in the balloon PV 12 atm300 L n 15 moles RT 0082062925 K The gas in the balloon is actually a mixture air Does this change your answer No it doesn t Each gas in a mixture acts independently 130 Dalton s Law of Partial Pressures In a mixture of ideal gases the total pressure is the sum of the partial pressures of the individual gases Pt P1P2P3 otal otal X1 mole fraction of 1 moles of 1tota moles 131 Molecular View of Dalton s Law of Partial Pressures Piston depressed gt Closed III PA Ptotal PB Ptotal Ptotal PA PB 050 atm 10 atm 15 atm nA 030 mol 173 060 mol ntotal 090 mol XA 2 033 mol X3 067 mol n IIEE I ll F39A UUIIISIUIIS UI I Jdl lIUIUb PB collisions of B particles 132 The Molar Mass of a Gas Eiiiiiii iii ii ii i ii 133 Density of an Ideal Gas The density of an ideal gas does depend on its chemical identity molar mass molar massP density RT Gases are compressible density varies dramatically with changes in Tand P 134 Summary of the stoichiometric relationships among the amount mon of gaseous reactant or product and the gas variables pressure P volume V and temperature T amount GnoD of gas A Meal idea as molar ratio from as g bmancedequa on g IaMI law 135 Gas Stoichiometry The ideal gas law can be used to determine the amount of gas present for a stoichiometry calculation PV PV nRT n RT n moles of gas 136 Diffusion the spread of particles as a result of random thermal motion 137 Diffusion How fast do N2 molecules move 2 3RT 8314 Egmjegs K u S mo39K 515T1150mph M S 280x10393 Lg mol Copyright McGraw Hill 2009 138 Diffusion If molecules move so fast why do they diffuse so slowly Each molecule collides roughly every 1 ns Their mean free path is 70 nm or 103 molecular diameters mean free path the average distance a molecule travels between collisions 139 Effusion the escape of molecules through a tiny hole into a vacuum 140 Effusion 141 Effusion the process by which a gas escapes from its container through a tiny holeholes Graham s law of effusion the rate of effusion of a gas is inversely proportional to the square root of its molar mass Postulates of the KineticMolecular Theory Summary Postulate 1 Particle Volume Because the volume of an individual gas particle is so small compared to the volume of its container the gas particles are considered to have mass but no volume Postulate 2 Particle Motion Gas particles are in constant random straightline motion except when they collide with each other or with the container walls Postulate 3 Particle Collisions Collisions are elastic therefore the total kinetic energy Kk of the particles is constant 1 42


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