Lecture 01. Chemical Equilibrium Pt. 1.


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Lecture 01. Chemical Equilibrium Pt. 1.
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Arasasingham, Ramesh D.
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UCI Chem 1C General Chemistry (Spring 2013) Lec 01. General Chemistry -- Chemical Equilibrium -- Part 1 Instructor: Ramesh D. Arasasingham, Ph.D. UCI Chem 1C is the third and final quarter of General Chemistry series and covers the following topics: equilibria, aqueous acid-base equilibria, solubility equilibria, oxidation reduction reactions, electrochemistry; kinetics; special topics. Index of Topics: 0:12:18 Calculate Species at Equilibrium 0:25:24 Writing Law of Mass Action (Kc) 0:37:17 Steps for Writing Law of Mass Action
good morning on this is that the water the General Chemistry sequence so I don't think I need an introduction but will come to this class I see a lot of familiar faces and we are going to pick up where we stopped last quarter but before I I begin I want a kind of remind you that my primary mode of communicating with you will be through the class website are right and so it is important that you check the the class website often particularly the 1 that sees announcements because I will be putting on putting material there and isn't so what appears at on that before you come to class sometimes I'll put some notes there I'll put some extra problems there is important for you to check that as often as you can and print out material that's there OK so I am not because you've already taken this class you know these classes before and this is the 3rd quarter I'm not going to go into the details of housekeeping alright on the dates when you have a mid-term examines how the grade distributions worked out all that information is on the classic website you can read I'm not going to those details with you because you already know what it's however I do want to remind you that if you want to do well in this class there are 3 elements to this class and you all know what those elements are the 1st coming to lectures as all of you know it is important to come to lectures because as I said before I am here to advise and you don't always to guide staking you obviously you're not going to know how to prepare for the chance are textbooks have very often written as encyclopedias are right that they have lots of information it's impossible for you to kind of navigate through all the information that's provided in general cancer textbook all right so I'm going to emphasize things in class this quarter the material that we are covering actually involves a lot of numerical problem-solving now we moved on we look at the fundamentals of bonding now moving on to looking at equilibrium and later I will look at electric chemistry will look at him kinetics and so on and the topics and 1 seat of very heavily weighted towards numerical problem-solving and so I'm only working lots of examples in class because 1 of the ways in which you teach problem-solving skills is to model how experts solve problems have approach problems how to resolve these problems and particularly challenging problems are so I don't know what lots and lots of examples in class and so it's important that you come to class because you can see the work all these different types of problems and show you how to approach and solve this problem and so said don't come to lecture even miss out on that occasion so much is an important but as all of you know lectures has the disadvantage in that you're very passive I'm doing all the talking in euros see that is listening to me and in that possible your mind can wander already it's wandered off you know and and come back and so what you do doing periodically you paying attention and that's not very good up but the reality is that in many large-scale instruction like this we have to get to the material and the reality is that the election mode of instruction is not going to change all right when you have such big lecture halls so in the lecture very often you the passive litigation involving asked you to come prepared and ask you to a question that you can expect you to give me answers and sometimes that would make you do the problem in class I write so come prepared so that's electrified but we also have the 2nd element to this class which is discussions and because is so passive during lectures in discussions and I expect you to take control of the discussions discussions aware you want to do the work a work the problems the the 1 ask you to come forward it's OK to make mistakes discussions on to make mistakes and learn from the mistakes so there so that she is going to make you come up and answer questions and so on so the discussion is the place where you are going to be really engaged and you have to come prepared to discussions and you have to actively participate in discussion so we don't want any anybody sitting in the back and copying the answers because that's not really what we wanna do want you To be involved a case so discussions aware given the very active every discussion as you know the prior week I will be putting up a worksheet and those worksheets have represented problems again because it's so heavily weighted towards numerical problems the content would cover covering right now and so I will give you lots of different problems and give you opportunities to practice as well a cake so it will be a good idea you could try them that discussion problems prior to going to discussion so that you know we were discussions you can actually ask a lot of questions that he has been asked to come forward and work the problems on the board and people like to point out why it's wrong and so on and so if you come prepared it's very helpful a case of the 2nd element to this course is discussions and as all of you know attendance and discussion is mandatory we will Mark attendance in discussion and of course the 3rd element is homework or at all 3 elements are important
and for this class you have online homework you all of you have seen on the online homework and have tried it before and the whole that we are going to be using its catalysts so each 1 of you will be getting an individualized homework so your homework is different from the others in your class and remember the goal is is mastering the goal is not to just complete the homework for the sake of completing the homework it's not a one-shot deal you can't do the homework as many times as you wish to every time you restarted it's going to be a fresh set of problems all right and the goal is that you achieve mastery so you can work at 4 times 5 times as long as you achieve mastery and we call that you have to achieve 75 per cent of morning work alright if you could use cost only 5 per cent or more on homework that counts is getting 100 percent annual work right so once again you have an opportunity to practice which you've learned using the online homework but I want to remind you that online homework is an automated system and there's only so much computers can do and so were all my homework really works is where you get a lot of practice in other words the practice of fundamental basic stuff or some stuff that you have to learn by rote before you can actually work more complex problems so they now that give you is what I've given you before it's likely no multiplications you know we need to learn at some point that in times 3 6 and 3 times forced 12 and so on and on homework is very good at getting into practice that but it is not very good at giving a very complex problem will you bring in multiple concepts together putting them together and solving a a complicated problem where you have to synthesize the information and use it in creative ways all right however if you want to get to that stage you have to get past the algorithm make practice type problems where you have gone through just the basic stuff you understand what it means when you say you have you with calculate equilibrium constant you have to know what it means when you're looking at a lot of mass actions also the fundamental stuff that we expected to to know what you're going to solve more complex equilibrium problems so the island homework is very good at getting you through the fundamental stuff and making sure you know the basic stuff but it is not very good at giving you very complex problems that you have to synthesize the information in order to do that I'm also a sign of few entered Chapter problems for new textbooks are right however the textual problems you do not need to turn it in but I know and I don't overloaded with work so I would choose a few examples problems that I would What I would like you work from the end of chatter problems in your textbook and the solutions to those problems are available in the back of the textbook we're also placed the complete solutions manual on reserve at the library said you can't solve a problem and you can come see me during office hours are considered 2 years during the office hours you can actually to the library and it's at the front desk it's unreservedly condemns you take a look at it and you want copied Kansas going down and down the hallway and use 1 of those copy machines to copy that particular PGT wanted to write so there are 3 elements to this course and I liken it to a three-legged stool it shows this is not a two-legged stool you you choose to not do homework you choose not to go to discussion with the things that happen it's not going to be very stable RI said you want to do well in this class you want to benefit from this class all 3 elements important because all 3 are integrated with each other each 1 reinforces the other and I rely on you to good discussions I rely on the UK online homework and I rely on you to come prepared to class is declaration so that's all that and talk about the mechanics of this class are right now before I proceed and started the material could today Is there anything that you want to ask me any questions all right so let's go let's start and then begin by reviewing a little bit of the material that recovery last quarter now the theme for this quarter is actually continuing chemical equilibrium should would go on looking at acid-base equilibria which happens to be Chapter 11 from a textbook however it is important that you know Chapter 10 really well Chapter 10 deals with the fundamentals of chemical equilibrium state means that you have to have a good understanding of the basic principles that we looked at last quarter because you understand those principles now it's a matter of applying them to different scenarios so you understand what chemical equipment is now undertake different kinds of chemical equilibrium and look at them in greater detail and the first one that will start by looking at is looking at acid-base equilibrium OK but before doing that I wanted kind of review some fundamental aspects of the material that recovered last quarter and I wanted to take 1 critically examined way kind of review the material is actually what the problem and we welcome a complex problem and those of you took my class last time you know what I'm talking about because I want to show you different strategies of solving the problem and undertake a problem that I did work last quarter but is a really good example and for the benefit of those who were not in my class last quarter I want to go through this for example in with any kind of look at all the main points as we go along so so I put this
problem on the last website so I really don't want to copy the problem I wanted to pay more attention to the strategy of using assault problems for some reason this this is not focusing very well today so so where did equilibrium problems and we're going to use this sort of general strategies that we used to solve the equilibrium problems and I apologize for this I do not know what I think that of there were right keep your fingers crossed itself the secularist problem saying given an equilibrium arrived and told that at 35 degrees Celsius Casey for this equilibrium is given to you calculated the concentrations of all the species that equilibrium for the following the regional mixture write to insolvent equilibrium problems where is the starting point would you look at what was obviously you need to look at which of the balanced equation we we start with the balanced equations never assume that any balanced equation provided to you is actually bounced always checks because there can be typos and sometimes people give you the equation without balancing in and it's unbalanced you need to know that its unbalanced nite turns out this equation is about so we stopped by writing down the balanced equation and the physical states and as a rule of thumb I always suggest that you write the value of the equilibrium constant as well right next to it as a reminder to you alright what the magnitude of that will constant all right and it turns out this is 1 . 6 times 10 to the negative 5 are right now all of you know that equilibrium constant is called a lot of mass action or it's the equilibrium constant expressions are right and how do you write the Loch Ness action it's always defined as well the concentrations of the products raised the part of the coefficient divided by by the concentration of the reactants raced to the park question so the bottom line is that when you look at the lot mass action of equilibrium expression the products of the numerator and the reactions of the denominator all right and so essentially gives you roughly the ratio of products to react so the bottom line is it's not important to me that you know how to write the lot mass actually I tell you guys that at any rate it can write that in view of human balanced equation riding the loss mass action of the equilibrium expression anyone can do it if it doesn't require any but prior knowledge what's more important to me is that you understand what that number tells you remembered equilibrium constant gives you the ratio approximate ratio of products to react as were the products of the numerator and the reactions of the denominator so what she'd the numerical value of k tells you is what they call them composition looks like it tells you what is that it could be a mixture look like it tells you whether that mixture has lots of products and very little reactants so you can value is much greater than 1 so let's say the value of the order of a thousand UK is the value of the the order of a thousand what does that tell you about the equilibrium mixture lots of products very little reacted so it gives you an idea of the composition of the mixture and that is the most important taken message because the equilibrium constant gives you an idea when the caller was established with the mixture of reactors and products look like that so now let's look at this and this number is 10 to the negative following is that a number now has a rather gage in your products and reactions were 50 50 mixture watching the value of cake amount to approximately 1 so and equilibrium when it plans established you have affected the mixture of approximately 1 if the number is far greater than 1 we know that the mixture now should have lots of products and very little reactants now this is genuine Native applied so this number is much much smaller than 1 so what does that tell you about that equilibrium mixture lots of reactants very little so that is this reaction took place only to a small amount you see that it reacted just a little bit and established equilibrium are right and we use the term the extent of the reaction to describe that all right and so you want described in terms of the extent of the reaction this reaction react to a large extent before establishing equilibrium or go to a small extent before establishing an equivalent small extent you see that and that's important because with the news that the so 1 of the things that you get a feel for is by looking at the magnitude of and then if that number is really small you know that only reacted to a small extent if that number is really lots instead of attended to the negative 5 it's 10 to the power of quiet waters that mean it reacted to a large extent so what that means is like you have almost 99 cent product and 1 one-percent reacted to see the roughly and using this approximate numbers but it means that it reacted to a large extent and it's tend to the positive by its large extent 99 cent about 1 per cent reactants if extend to the negative find what does that tell you you have only 1 % product and you have 99 per cent of on reacted reactants do understand that so that's the 1st important take a message and that's why you write the key value right now right next to the equilibrium so that when you look at the man the number you have an idea To what extent that reaction took place all right so now we start by writing down all the information that provided to us so we given the concentrations of NO CEO so were told to hold a pure and out in a 2 1 lead last arrived selves since were given moles the units that are provided ,comma moles and volumes now wouldn't think of it this in terms of concentration because member in equilibrium expressions of lot mass actions you can either given in terms of concentrations or if they're all gasses you can give it in terms of pressure all right because pressure of gasses is directly proportional to concentration as well and that's why you can give them into different unions are right as long as the gasses are all gasses then you can give in terms of atmospheres or you can give in terms of concentration but it turns out here we've given concentrate moles
and volume and as all of you know what is the definition of concentration it's molds divided by volume all right so this is moles and this is volume in liters and therefore the unit is 1 moles per liter are right so we're looking at is gas would given that the number of moles of each 1 of those gasses or in this case is only 1 reactor and there's only 1 substance there to begin with and so what with the concentration come out to me it's 2 malls divided by 2 leaders and therefore my initial concentrations to begin with all right so my initial concentrations mold Khaleda all-white what is mole spore leader synonymous with Milan OK you know that malaria most leader the same thing and unit of concentration and and therefore my initial would be before any reaction takes place it's at times 0 before any reaction starts at time 0 is initial concentration so before any reaction takes place we know that the concentration of NOC others to moles divided by 2 leaders so where does that come out to be 1 more leaders and 0 yes We Have No products to begin with now the loudest system the goal equilibrium but remember these are reversible reactions and therefore the reaction can take place in the forward direction or it could take place in the reverse direction so I have to figure out is the reaction when it goes to forming an equilibrium is his reaction preceding the floor direction or proceeding in the reverse direction and although we recognize that we have no products when you have an equilibrium you have to have mixtures of reactant and products so there is no product what is obvious direction with the reactions that take place forward became there another way you can do this and you learned about the last time you can calculate what Q are right here was a reaction cautioned which the ratio of products to reactants before any reaction takes place what is here you your products 0 what is Q 0 so there's only 1 week you can go it's got From 0 it's got to go to tend to the negative fight to understand that and that means it has to go to with products as well so if you given the amount of reactions and products the new company Q and you have to figure out which direction the reaction will proceed in this case it's going to proceed in the forward direction all right and so was proceeding in the 4 direction and women saying that were let's say it is X is the amount that's used up we know that it's moving in the forward direction therefore the concentration of this has to go down and the conservation of the products need to go out when he was established and is going to proceed in the 4th direction and some of this is going to be consumed and some of these 7 informed so let's say the amount that's concealed is 2 because the coefficient here is to and because of this balanced equation we know all that the ratios are maintained by every 2 malls that's consumed a product performed 2 moles of theirs and 1 more of that so that ratio is always maintained that the ratio in which they react so for every 2 malls that concealment you have to mow the meadow being formed and 1 more of C O 2 being formed to 2 X is being concealed what does that tell you about the amount of and no that would be last to because you know that we put a plus sign to remind us that it's being and over here the is once said that should be process so that means at equilibrium what I would have there's 1 minus 2 acts this would be to X X as an accessory so when equilibrium is established you want the concentrations of reactions and products that expression describes it and if we can calculate what the value of says then solve for theirs and accurate algebraic expressions offer acts and figure out what is the concentration of annual CIA-led equilibrium what is the concentration of in what is the concentration of C O 2 so in order to find out what taxes we need an algebraic expression right we need to relate X to something else that the approach the problem provides are they have to you know it didn't give us any additional information we could not solve this problem and 1 that additional information would make use of the equilibrium constants are right so we can turn the lot mass action and that he planned must take that out so no 1 will want to writing the lot mass action which airs Casey so we can say Casey it is the concentration of the products racer part the coefficient kind CL to raise the power 1 divided by NOC Race to the power to do so this is the last mass action or this is the law of chemical equilibrium are right and have we that Casey it is 1 . 6 times to the negative 5 moles per liter memory equilibrium constants do have units are right and those units will depend on the long mass action right so this is the key value and this equals NL it would be too that's square that's a conservation of NO times x divided by 1 minus 2 x squared take so that gives me this historic squared times acts that reasoning for excuse 1 one-liners 2 acts right now 1 of the biggest headaches of solving equilibrium problems as all of you know Is the Algebra I made this point we straightforward but now you have to be able to solve X all right and sometimes this can be very complicated and you had a good calculated that could solve their wallets good but remember on an exam and you won't have the luxury of having our you know sophisticated program that can solve the algebraic equations for you all you have is a basic scientific calculator and you can see that the universe of basic scientific calculator this is gonna be hard to to solve so 1 of the challenges they have when you all these equilibrium problems it Montreal and what's that contract he the simple alright you can keep them out simple the chances that will make careless mistakes gets better and it turns out that your answer should be the same as if he were to solve this you know go through the whole process of solving that so here 1 thing things 1 way in which we keep the Mac simple is we make intelligent approximations all right and so let's look at this equation in this equilibrium if you look at that on a scale we said OK strengthening fight and take a stand donated by Reese said that because that country is so small we know that the reaction only proceeds to a small extent all right if it proceeds to a small extent what does that tell you about acts limited only reacts so that 1 % of reactor goes a product 99 % remains on reactive so what does that tell you about extant addicts the largest the small small pain so you have a scale it on this scale we have 100 % reactants here on this scale we have 100 % products all we hear about this is initially when we started this is we have only 100 % reactor In the reaction proceeded
100 per cent because the completion then what would happen you have 0 product 6 0 reactor 100 % products it when he delivers established your somewhere here what is that now when he was established right in the center is a 50 50 mixture so that means king of the approximately 1 day to see that we owe this case tends the negative fight so order that tell me about Casey Casey when he claimed was established and if you look at the ratio products to react and you know that you have lots of UN UN reacted reactor and very little products are right so you look at this whole range of looking at the ratios of reactions to products you can have 100 % reactant that means no reaction is taking place you can have 100 cent product that means an example where the reaction with completion did establish equilibrium just went to completion is right in the middle what happens when includes establishing a 50 50 mixture if it's on the right-hand side of the it's somewhere here what does that tell you you would have 75 cent product and 25 % reacted to see that right so we're over here and so this is where equilibrium is established so that we can that it reacted only to a small extent and that's what excuse you the extent of the reaction is the amount that reacted and we know that that X is going be really small because and only reacted to a small extent
no because this X's really small because chased Interlaken 5 now that gives us a way to make an approximation because we know that the only reacted to a small extent and therefore to keep my mouth simple now and then make a smart approximation and my approximation is that 1 minus 2 ex-member I want simplify this expression all right and so if you start with 1 molar concentration and reacts only to a small extent wilderness back to where is so small 2 X is so small compared to 1 To compared to 1 molar we can neglected so this is an assumption that you're making it's an approximation it's very subjective you understand that anybody can make any approximations I wouldn't start by by making approximations but then we have to go validated make sure that approximations actually valid or not the case so that this assumption thanking say that we met this approximation it considerably simplifies my map because now I can say at 1 . 6 times 785 5 malls for leader equals 4 X Q divided by 1 now what would have turned out to be horrible algebraic equation to solve now I just boils down to a simple steps all right now all I have to do it's divide this number by 4 and take the route Cuba that and so on you work that out the comes out to be I'm so you solve a X X comes out to be 1 . 6 times 10 to the negative to member excess concentrations of the unit for that should be be most the leader Milan right so I made this very subjective approximation and anybody can make any approximations you understand that alright but what I need to do now I had to go but I have to go back and make sure that my approximations valid know what was my approximations go back and ask yourself what is your approximation 2 acts is small compared to 1 so we need to find out is to it's really small compared to 1 so my validity will be Sunderland checked the validity of my approximation all right and my validity is that what I'm saying is to address is really a small compared to what some take the ratio of the 2 and find out what percentage is 2 x
compared to 1 all right so once again you have to go back it's not exercise not saying excess small compared to 1 in that approximations linked to access small compared to 1 and if I have to compare to act with once you get it and so I would go back and said 2 times 1 . 6 times since the negative to Moeller divided by by 1 more times 100 And if you work that out that comes out to be 3 . 2 center so that tells us is that if you compare 2 x 2 1 2 X is 3 . 2 per cent of 1 all right so now I have to ask yourself is that good enough and so we have to do is purely arbitrary rule and we call it the 5 percent rule it is approximately 5 per cent or less we know that it's a really small number and they can be neglected all right and so because it's falls below this opportunity fight sense that we pick our right now we know that the approximation is valid OK and we know the 2 X is indeed very small compared to 1 right so we say approximation is valid or not let's say
you did you made this approximation and cannot be 25 % so what does that mean but you can't that approximation all right and that means that you have to to go back and you have not that you just have to grit their teeth sit down and solve an algebraic equation jurors said that there's nothing you can do about it I it turns out in this case you can and where that clue lies where is the clue lies when you can make those approximations Tennessee if Casey as well as small it stands the negative for 85 containing it's 6 those of relatively small numbers the case that is the extent of the reaction has to be really small and therefore you can make that approximation now we need to calculate the concentrations and so we go back now we have that the problem is still not complete because now we need to figure out what the concentrations of the concentration of NOC our is 1 minus 2 acts right which is 1 miners 3 . 2 times tend to negative to smaller and that comes out to be I'm sorry in Osceola ,comma to be . 9 7 bowlers and all concentration of NO is 2 acts which is 3 . 2 times intending to Mohler and the concentration of C O 2 His acts which is 1 . 6 times tend to negative to more right you know what's interesting is if you did not make this approximation and that's all that algebraic equations in the same answer all right and so it makes it much easier if you make this approximation therefore solving problem it's easy right now that the 2nd part of the problem in the 2nd part of this problem and so can I remove the side-by-side with this so let's go back to to and now we told that things have changed a little bit now we have a different scenario where we have 3 and all and 1 wall of C O 2 in a one-liter last rites of the same things so I go back we start by writing the balanced equation make sure you look at the physical states because of physical states give unite idea a whether it's a whole system or had to do this system and a lot of mass action does depend on whether it's a homogeneous system for system these are all in the gas estates of a homogeneous they had to the homogeneous OK so once again right Casey to remind you that this is a very small number now is the right down the initial concentrations in malls for leader of malaria they tell us that we have 3 molds of NL in a one-liter last so what is the concentration of NO 3 most Polito and I have 1 mole per liter of C O 2 I'm not putting the units there because I'm putting that Francis's dead and it reminds us that we units of concentration and we don't have any reacted so what does that mean you have 0 so insulting in equilibrium problems this is what you have to begin with so it is the 1st question you ask Member equilibria are reversible reactions that can proceed the forward reaction of the restrictions in this case which direction is that reaction proceeded to reverse alright so now we have no problem no reacted so we know that equipment established we have to have some react and therefore we know put this Arab to remind me that that's the direction in which the reaction from the place are right if the reaction is taking place in that direction then they were looking at the relative change is proceeding in this direction and so what would best come out to
me to tell me what put here -minus miners was to x fear minus X
and on this side plus 2 X because now the reaction is proceeding in the reverse direction so products that would be consumed to form reactants because products are being consumed you put the negative sign to show that you concentration is decreasing on the product side and the conservation increasing on react in such a case therefore when equilibrium is established this would be to access this would be 3 minus 2 X and this would be 1 minus X rigorous within the now return to the law of mass action we know Casey equals 1 . 6 times and the negative 5 miles per liter equals again the fall in which this equilibrium is written is that these are the products of these other reactants right so long as section would be an old square and oversee all too divided by NOC elsewhere which an old would be 3 -minus 2 x squared times 1 minus X divided by 2 x squared got it so now ask yourself can I make an approximation here now the reaction is proceeding in the reverse direction what this kid tell me that had equilibrium what will my composition look like an equilibrium case tends an 85 so regardless of whether reaction force in the former direction of the reverse direction what will make encompassing look like lots of products are very little products very little can you see that because many clues established my numerator products have to be small so I had very little products and lots of reactants To get very little products and lots of reactants what would the magnitude of his extra command to the largest mall clause so now the sex is really big so punitive taxes will big can I say that to excess small compared to 3 not that to it is really going to cost to treat you understand that so here I can make approximation right and I can make approximation then I had to sit there and solve this algebraic equations on this you have a computer that can solve this equation you won't be able to solve this equation you know in a classroom Gerson and so like I said before we have a problem which are right and therefore I'm just a few of my arms and say I can't do it I cancels solve this equation right but remember part of solving equilibrium problems is coming up with clever strategies all right and the stranded of news here is that once again that go back to last member we said if you have 100 % reactants over here you have 100 percent products and for this equilibrium we know that Casey is right here all right but we started with 100 percent product right so our our problem was his that we started here and we proceed this way and here X is large so you know approximation and that creates a problem for us all right so the other alternative is that we know that whenever the reaction proceeds in the forward direction Texas small when it proceeds in the reverse direction X is going to be large alright so instead of making the reaction go this way what I'm going to do is I'm going to make it go 100 percent this way all right and let all the reactants good product and then I'm going to let it go in the forward direction you see that so by making a gold 100 cent this way and then making eagle here this act it's going to be a small all right so our strategy is now To keep them simple environment reaction when the floor direction and now I can make
approximations X really small all right under call that why because I don't want to be a confused it except there because we use just everywhere so let's say that I'm going to call this what Kate so so we have 100 percent reacted you 100 some product there so hard lesson about doing this summer's start with 2 NOC gas giving me to an old gas plus seal to gas Casey is 1 . 6 times and the negative 5 malls per liter so I'm going start with my To begin with what I have is 1 and 3 and 0 now general strategy is going to be that and they make a go 100 % political equilibrium understands let 100 per cent so when I let it go 100 cent and I have a new initial now I'm changing things around in my new initially would be when this reactor 100 percent to give me products are right so if it with it's reacting 100 % has eliminated a problem it's a reaction that goes to completion right so that eliminating region problem we look at these 2 reactants and figure out which is the excess reactor and which is the limiting reactant are right now you take sealed to remember the reactor 1 2 ratio if all of this was concealed how much of this wouldn't need 2 cases that it only uses up too much is left over 1 so that means all of this is used up and this will react with only the tools of this for the past 3 so this is the excess region and then have 1 of those reacted to comments product would fall on side too all right so now might change would be now I'm making the reaction when the 4 directions and now it's proceeding now that have shifted alter 100 percent in order to establish equilibrium I know that has preceded the forward direction are right it's proceeding in the 4 direction and I know this will be negative to y this would be a plus to why this be life and is using why so that you don't confuse it with the X from the previous example where we can solve equation pain so therefore at equilibrium the concentrations of B to minus 2 this would be an 1 plus 2 wide and that would be wise all right so now I can say Casey equals 1 . 6 times since the negative 5 miles per liter equals the concentration of NO squared times the concentration of C O 2 divided by the concentration of NOC all-square which gives me 1 2 while squared times y divided by 2 mines to wide square that now I can simplify the map because now I can make an approximation and I can say my approximation is that 1 plus 2 it is 1 in other words to why is so small it can be neglected all right and to -minus 2 wives will equal to as well all right so now I can see that case equals 1 . 6 times and the naked 5 malls for which equals 1 square times y divided by 2 squared which is why well hurricane is seeing now my Mac has got to be very simple and survive software and X comes out to be 6 . 4 times 10 to the negative finding tools for leaders so now by making this taking this approach I've survived a match considerably are right and that can new that company check the validity of our what is my validity here I'm saying to acts is small compared to 1 of 2 why such a validity and then the new guys at home figure out what the concentration of NOC other areas where the concentration of an and what the concentration of the opportunities arise
and just check and stares at the beginning of plastics the


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