Unit1Day5 VandenBout Tuesday September 10 2013 3 15 PM Vanden Bout LaBrake Crawford CH301 LIMITS OF THE LAW MIXTURES Day 5 CH301 Vanden Bout LaBrake Fall 2013 Important Information LM 10 11 POSTED DUE Tue 9AM HW 3 POSTED DUE Tue 9AM LM 8 9 WERE DUE THIS MORNING 9AM CH302 Vanden Bout LaBrake Spring 2012 What are we going to learn today LIMIT OF THE IDEAL GAS BEHAVIOR Unit1Day5 VandenBout Page 1 What are we going to learn today LIMIT OF THE IDEAL GAS BEHAVIOR What is a model When does it fail REPRESENTING GAS MIXTURES Concept of Partial Pressures CH301 Vanden Bout LaBrake Fall 2013 QUIZ CLICKER QUESTION 1 points for CORRECT answer The Kinetic Molecular Theory is a physical model based on the all of following assumptions EXCEPT a The particles are infinitely small b The particles are in constant motion c The particles exert no forces on each other d The particles have elastic collisions e The particles lose a little energy to the walls of a container when they collide CH301 Vanden Bout LaBrake Fall 2013 Unit1Day5 VandenBout Page 2 What about the mass If the impact is related to momentum Shouldn t more massive particles have a higher pressure QUIZ CLICKER QUESTION 2 Question In a mixture of one mole of He and one mole of Ar the partial pressure of the Ar compared to the partial pressure of He is A The same B Higher C Lower CH302 Vanden Bout LaBrake Fall 2012 What about the mass If the impact is related to momentum Shouldn t more massive particles have a higher pressure QUIZ CLICKER QUESTION 2 Question In a mixture of one mole of He and one mole of Ar the partial pressure of the Ar compared to the partial pressure of He is A The same B Higher C Lower CH302 Vanden Bout LaBrake Fall 2012 Unit1Day5 VandenBout Page 3 Engaging in practice matters Illusion of Understanding Watching isn t the same as doing Maximize Learning Opportunities test your understanding make mistakes receive coaching CH 301 Vanden Bout LaBrake Fall 2013 What did we learn last time Ideal Gas is amazing empirically derived and also theoretically derived We now know how to relate rms velocity to both temperature and mass We can apply our knowledge of velocities to diffusion and effusion of gases Finally there is a distribution of velocities This will have huge implications for future understanding of chemistry CH302 Vanden Bout LaBrake Spring 2012 MASS DENSITY FOR GASES THINK BACK TO BALLOONS SAME T P DIFFERENT DENSITIES WERE DUE TO THE DIFFERENT MASSES OF THE GAS PARTICLES WHAT ABOUT MIXTURES Unit1Day5 VandenBout Page 4 DIFFERENT DENSITIES WERE DUE TO THE DIFFERENT MASSES OF THE GAS PARTICLES WHAT ABOUT MIXTURES CH301 Vanden Bout LaBrake Fall 2013 How to describe a mixture Two containers of equal volume separated by a wall nHe mole He T 300K P 1 bar nAr mole Ar T 300K P 1 bar Same V P T therefore nHe nAr CH301 Vanden Bout LaBrake Fall 2013 Mixtures Remove the wall Total pressure is still 1 bar PV nRT What is n now n is the total number of moles of all the gases n nHe nAr 2 x nHe CH301 Vanden Bout LaBrake Fall 2013 Unit1Day5 VandenBout Page 5 Partial Pressure Total pressure is still 1 bar Where does the pressure come from We can think of dividing it up into the Pressure from the He and the pressure from the Ar CH301 Vanden Bout LaBrake Fall 2013 Mixtures Half the particles are Ar so half the pressure should be from Ar PAr nArRT V nAr is half the number of total moles So PAr is half the total pressure CH301 Vanden Bout LaBrake Fall 2013 Mixtures The same is true for He Unit1Day5 VandenBout Page 6 PHe nHeRT V nHe is half the number of total moles So PHe is half the total pressure CH301 Vanden Bout LaBrake Fall 2013 Partial Pressure This is what we call partial pressure In a mixture the partial pressure of gas i Pi niRT V CH301 Vanden Bout LaBrake Fall 2013 Dalton s Law The sum of all partial pressure must be the total pressure CH301 Vanden Bout LaBrake Fall 2013 Unit1Day5 VandenBout Page 7 Mole Fraction Percentage What fraction of the particles are gas i CH301 Vanden Bout LaBrake Fall 2013 Mole Fraction Percentage What fraction of the particles are gas i Mole fraction Xi is the number of moles i divided by the total number of moles CH301 Vanden Bout LaBrake Fall 2013 Unit1Day5 VandenBout Page 8 Air By mole Air is 21 O2 CH301 Vanden Bout LaBrake Fall 2013 POLLING CLICKER QUESTION 6 Air In this room what is the partial pressure of O2 Numerical Clicker question Give your answer in atm CH301 Vanden Bout LaBrake Fall 2013 Unit1Day5 VandenBout Page 9 Air Mole fraction of O2 0 21 P02 XO2Ptotal 0 21 1 atm 0 21 atm CH301 Vanden Bout LaBrake Fall 2013 Scientific Model A description of nature that can predict things about many similar situations A good model must be able to explain as many characteristics of these observations as possible but also be as simple as possible A good model should provide physical insight What happens when a simple model breaks down CH301 Vanden Bout LaBrake Fall 2013 Unit1Day5 VandenBout Page 10 GROUP WORK HARD SPHERE MODEL WORK IN GROUPS DIVIDE UP THE WORK TO COMPLETE THE DATA TABLE AND THEN DISCUSS YOUR RESULTS CH301 Vanden Bout LaBrake Fall 2013 POLL CLICKER QUESTION 2 Under what conditions does the Ideal Gas Equation of State best model the real gas behavior Talk amongst yourselves then answer a High pressure b Low pressure c High temperature d Low temperature CH301 Vanden Bout LaBrake Fall 2013 Under what condition does the Ideal Gas Equation of State best model the real gas behavior Low pressure WHY Unit1Day5 VandenBout Page 11 Equation of State best model the real gas behavior Low pressure WHY From the molecular perspective what is going on CH301 Vanden Bout LaBrake Fall 2013 Low pressure From the molecular perspective what is going on P increases V decreases V constant P As P gets very large V goes to zero http ch301 cm utexas edu simulations gas laws GasLawSimulator swf CH301 Vanden Bout LaBrake Fall 2013 Breakdown of Ideal Gas High Pressure Low Volume volume of particles starts become significant Particles can t exist on top of each other Low Pressure Large Volume volume of particles doesn t matter The available volume is the volume of the container minus the volume of the particles CH301 Vanden Bout LaBrake Fall 2013 Unit1Day5 VandenBout Page 12 At high pressure need to account for volume occupied by the gas particles themselves Different sized of particles now matters CH301 Vanden Bout LaBrake Fall 2013 HARD SPHERE MODEL At high pressure need to account for volume occupied by the gas
View Full Document
Unlocking...