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Lecture 09. The First Law (review) & Adiabatic Processes Part II


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Title Lecture 09. The First Law (review) & Adiabatic Processes Part II
Title of Series Chemistry 131C: Thermodynamics and Chemical Dynamics
Part Number 9
Number of Parts 27
Author Penner, Reginald
Johns, Gianmarc
Contributors Johns, Gianmarc (Teaching Assistant)
License CC Attribution - ShareAlike 3.0 Unported:
You are free to use, adapt and copy, distribute and transmit the work or content in adapted or unchanged form for any legal and non-commercial purpose as long as the work is attributed to the author in the manner specified by the author or licensor and the work or content is shared also in adapted form only under the conditions of this license.
DOI 10.5446/18964
Publisher University of California Irvine (UCI)
Release Date 2012
Language English

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Subject Area Chemistry
Abstract UCI Chem 131C Thermodynamics and Chemical Dynamics (Spring 2012) Lec 09. Thermodynamics and Chemical Dynamics -- The First Law (review) & Adiabatic Processes Part II -- Instructor: Reginald Penner, Ph.D. Description: In Chemistry 131C, students will study how to calculate macroscopic chemical properties of systems. This course will build on the microscopic understanding (Chemical Physics) to reinforce and expand your understanding of the basic thermo-chemistry concepts from General Chemistry (Physical Chemistry.) We then go on to study how chemical reaction rates are measured and calculated from molecular properties. Topics covered include: Energy, entropy, and the thermodynamic potentials; Chemical equilibrium; and Chemical kinetics. Index of Topics: 0:01:16 Internal Energy 0:04:30 Heat 0:06:01 Enthalpy 0:16:47 Adiabatic Processes
story CAN to your discussion of thermodynamics of
a look at about across the seas so you've got a really
important thing to deal with interim economics is defining your system in your surroundings right it sounds trivial but it is not going to renew a couple examples and you see this so automatic system we wanna know how much energy the system has its internal energy you so you don't you is going to be the heat plasterwork pupils W. but some of the sign convention so in other
classes so perhaps you know you you got off easy on unsigned areas is the point off something like that when thermodynamics the sign is everything going to get the sign on the thermodynamics hits the difference between making a refrigerator and heater guide that's pretty wrong right the river
system and the surroundings so I think we have heat in work going from the system into the surrounding they will carry actions :colon I exit OK so you've got to keep going from the system into the surrounding and that's easy to see when your system is a parable box I believe stopped about example let's say combustion here at the beach with a bonfire of the loggers on fire and you pick it up and you burn yourself right the exit reaction going on seizing he it's going out of the laws will feature leaving the lot Eisenhower pick it up they have not so great so obvious right with you think about it this system is that say the Celulosa whatever is burning in that wall combusting so and you are part of the surroundings important thing with the romance it's not
about you right your part surroundings so if you feel that while you're feeling he transferred from the the from burning logs
interior and so that's the still holds up because it seems a little backwards it's not OK here we have long and wayward the constructive about how organisms in system would react by heat in work both going into the system so you worker-both going into the system with called the end of so I guess this is the end of the reaction not think about this so you got it and agree
action going on in the hood of your life and you grab the containers hot or cold called good because of and its
appalling heat into it right to say Well that's good that's got all this heat it was cold what polling that heat energy From the surroundings your hand is part of the surrounding that's why you feel cold up there 5 Stoneleigh it's pretty clear right which way it's going how do you know which way work is going where the equation for work so if it's got a negative for the PC with the only way that this right side can be positive if adopted the is negative so all I have to do is look at you change in volume and I'll tell you if there is all workers can be positive or negative and when you when you calculate this work calculating the work performed on the system not by the system so if you think about like a compressed air cylinders
Riley Gallagher a shock absorber in your car and you walk up a new push it down he did work on the right and the volume inside the cylinder got smaller so the pay attention to what happens
volumes is getting larger or smaller that don't the and and hence you get there you know which way work is done and so PT work as it's colloquially called is just 1 type of work we have a bunch of others but whirling and we deal with PV work in in this class C according to 90's others we we just
want you to be aware that that's not the only type of work you can describe by so that work
how about Q by so if we restrict worked appealing work and we look at our equation here we can substitute for work we can put speed up the Vienna right and that little .period just means constant pressure that's that that's therefore out so this is this is a particularly interesting situation for Khamis because most chemical
reactions are performed under constant pressure right if you have a reaction going on in the bigger that's open to the environment the pressures is is going stay the same answers can be 180 right so His
reactions carry out a constant pressure our our appointed interested chemist Somali carried out constant pressure but most of the time if you have a closed up system that's a bad thing regularly glass and I would explode so it is not me I have to wear glasses but I so I you is you as a monitor work so here or just explaining it out on expanding the delta's right to get dealt the UAE Tennessee adults so you know that means final minus initial so you get what you do is you want to expand our volume in the same there would some simple algebra and we can rearrange it this way so so we've got to use together the ones together the final in the initial are together here and there's a difference the reason we're doing that is you plus PVC it is also known as Anfal please so if we're able group those 2 together you can say the final moments and Poppe initial is equal for he so happily define he also changes and that we are assuming a constant pressure and also suing the daily work dealing with the speedy work which is the assumption that you can carry throughout this class I just got a little example here we've got 2 different minerals that conform from calcium carbonate cast light aragonite um nothing calcium carbonate even in the
ocean have it's in some it's dissolved in the water and that's what mollusks pull out of the water to create the shells this our cousin covering 1 fact against look
at this problem so the change in you when 1 mole of calcite is converted to regulators to 10 jewels from all calculated differently on so we want the difference between the end of the change in the change in the internal energy so we are different here Redway away what your differences thinks subtraction was on track in that and they give us the densities and the pressure at which were working so far so good on Anteby equation and here's asserts are at the B equation chair in terms of a changing such a gentle Pete Peterson get adult alliance constant pressure right so we define pressured being constant so it doesn't get out and we said we want the difference so that we know we're just gonna subtracted dealt you from both sides and we have a difference is good amount to up the Delta the Aurora work God so we've got beginners densities were adjusted the change in volume so will begin volume from density here but we know how many grams the stuff we have because we know Harry Moses also it's time to wait working away so if you divide that GM cancel your left with cubic centimeters so we know a change in volume between these 2 forms of the Calcite Miramar and can rewriting weary right as pastels times up meters so we're going to convert ITB centimeters to Pascal converter 1 bar Pascal's the reason for this is that pastels
times cubic meters gives you Jules if you don't believe me just Google Pascal's transmitters to that's what I did and their up doesn't it doesn't give website it just tells you Google gets bigger by the day so plug
everything we know are changing temperatures are out of the sky is retained in volumes the pressure we get negative point to a jolt so look at this this is only . 1 per cent of our total internal energy is represented by the PD work so what that reason we did this examples we want to realize that if you're talking about Delta you change in internal energy the changing and dumping if you did with
solids there almost the same number and it makes sense right because solids from 1 cell to another the vine doesn't change much and the exception of course is it with
really high pressures writing about pressure really high even adopted the is small we can get that number of overall so the so OK Sinaloa New Year's is graphically so on the bottom there we've got internal energy and other top we've got the and the area on so we think that differences between those 2 lines the With the burial but the difference between these 2 numbers that has that added to the appealing this is just what looks like graphically sulfuric plot and entropy is a function of temperature visited gratitude get and PV represents a difference but I so with some of the slow right say
tiny guys here slope you should always think derivative right at this point you careers you know slope derivative
automatic so the important thing to do it it's it's a partial derivative right so any time we take a partial
derivative we need a hold something constant and then find the slope in another direction right so
you can hold 1 of 2 things company can you hold volume constant and then you get heat capacity of constant volume for or you can pressure constant and unit constant said he capacity constant pressure so yes a partial derivative of inter-religious suspected temperature or at the plea with respect to researchers 2 forms of the capacity it's important specify which ones OK so now an example we've got this gadget here then I got elected leader hooked up to a block of copper there were going send some current through that and he this cover-up were going to measure the change in and from there as we should be able to figure out the heat capacity both of our
specific system here the block of copper animal in the capacity of copper in general so but got the over this
is a kid the guys can buy online so if you want do this at home and pressure from the
parties because shoveling the opacity of copper for now on show is the thermometer goes through
the years it's 75 and copper that rather than by supportive factor need to know to do this problem is that 1 life is equal to amps times the voltage Mobile to gather what they have described the flow of current right so that charged her time so how much charges go by part-time so fast the currents flowing through this is the dangerous 1 right if you get electrocuted I am insist is there's trouble potential in it's the answer kills you so that they can remember but here we have a revolt years and that's schools for Procol onto energy Pachachi while flying together :colon Colom's cancel and were left with jewels per 2nd so now we know how much energy per 2nd is being
transferred out from this electric heaters to the cops yeah and we also know that we
ran the heater for 19 seconds I so you multiply by the time you know so it's like Speed right going 50
miles an hour for an hour ago 50 miles I think to be about the same on same
forget 50 duel per 2nd you go 19 seconds you got 150 Josie just multiply so again 150 jewels OK which apply figure how many malls a couple were dealing with right because we want use both are the capacity of most of system in 1 employee so he discovered that the malls like interlocutors that guys and undoubtedly because I imagine OK so he can pass through constant pressure is a change the energy Over the change in time right so in this case are changing just heat right volumes not changing nothing like battery all
were worried about the change in the and he is such a transfer of
energy right so we transferred 950 jewels the temperature change by 33 Calvin therefore are heat capacity is Jules Patel it was not around here what the Moloney capacity so all you do is divided the heat capacity for your system by the number of malls that you're dealing with a new guy right now it's easy ones .period known react now what a thing about the change in ample pretty if you're heating 2 moles of oxygen from 24 degrees Celsius to 100 degrees Celsius at 188 look at so seat he capacity again but this time we're going to use encounter a little more of a slick
way so Vermont by by both
sides by DEC the most bubbles that DT could see how we get our DH by itself with DT their right so naked integrate both sides so integral on DT that's just going to be finalized initial right also known as Dr. H. by the DH rather so it'd DH we adults aged Nova nearly of an integral From our initial temperature to a final temperature of he capacitor constant pressure with the team so if we can find a way to express heat capacity with T temperature as a
viable we can solve that and go right as luck would have it we can do this said the kind of foolish
right now so there's any capacity there is a formula we express the capacity in terms of a variable temperature Indian see are just constants I see guys know that the ideal gas flow will then the walls came up with a more precise ideal
gas law but you can apply to actual gasses on so each guest with Withers oxygen nitrogen
whatever is going to have a different value for a B and C. so that's always a B and C such a form of free capacity that we can throw that into equation as a parameters we just talked about at what they are so the following year so what salaries of right side with his on them so the role of a conflict is committed constant times our adopted tea interval of tea is a T square over to an integral part of the squad of were 2 squared is my sorority right the use of force so plug-ins everything we know so is our follows we've we took those into girls and we just plugged everything we know in here at temperatures are constants and we know how much energy there really got
that guide OK case at
about 80 that processes OK so far a idiomatic process so 1st we take our normal rule here and there want talk about a change so if the if if you is changing so therefore accused JAG W's changing so we make it changes but now it's safer and adiabatic processes that are queuing 0 an adopt accuse also 0 for these changes but we can
still make changes to the work so if the Q 0 when
our saying the internal energy is equivalent at the change in internal energy is equivalent to the changing work for a media batik system I so make sure you know what these qualifiers are important you wanted to supply blindly right said "quotation mark "quotation mark it was but focus is just over with everything we've saying so now if we've got our DU now as in capacity deteriorate so the same equation for the capacity equation we much-publicized IDT again but now we're going to take this step that we know that if radium Batic that DU and W or interchangeable right so looking at this thing we've got that's a equation when you a subsidy W in there but the W we said the only ,comma work we're dealing with his PV were right so we put our our PTV in there but now we know deal with an ideal
gas for an ideal gas people's every time I write so instead
of writing pressure there let's just the same as entity over the right side took the ideal gas slot divide both cited by the so this thing right here is equivalent to pressure and Artie over there and this is the highest rate are variables vary we've got a DVD things Okinawa so but see was evident everything in our deal is equivalent to the W therefore we can bring this down here so he capacity DT is full of to minus arity over the Times Stephen so that we can now we can find a useful or expression for this so it's a really great both sides again will 1st of all it's too by both sides by TAT deputy with the DT interview with the BBC right that's important so we get all our variables when they need to be debate we performed integration so that the goal of 1 over axes Alibek scarce so we'll see absolutely we took the gold both sides and I see you've got Allen of of attempted near the end of volume here but it's going to be final minus initial right so the Allen 52 minus the Allen of 51 but if you
have to Alan subtracted from each other Corsican put those together right and just
but in the the same model that divide that so we did here but that make this a little more usable even left by both sides by CT would it got over there and then after we do that we'll put both sides as VX when you do this you get real on here on here and then this will be the exponent I will have the ads were worked up here
it's pretty simple asked me afterward the feeling that I am but you
get this equation so this is really handy because now we have an equation that if we know where 80 about it and we can relate change in temperature did change in volume given that all we know is our value which is a constant in our home he capacity with respect to a constant volume sorely to know these things and we can relate this to each other so now if you did this graph you were trying to show you so am I so Thurman is is the surface right and what it means is that if you have the system and eagerness sold like a compressed gas cylinder and eunuchs exquisite volume together the pressures bingo operator so going along this path this is if we hold temperature constant any change this volume that that's going to happen oppression and this is it any different temperature so now if we're talking about 2 different temperatures and we know it's adiabatic then I the the change here is going to be our larger for adiabatic analyzes thermal process so change in pressure is is going to be the larger so if you just and makes sense if you look at this they for going along on the Net I sit there it will see a change in pressure will just go here that right but if you go along the adiabatic process you go there there so along the path just intrinsically because you're jumping
from 1 surface and the other half of the so let's talk about
ISO thermal underwear his operation Frady back therefore that change figured that out isothermal will look at this that you become obvious to you write this down here we've got adopted the butterfly was just a regular they would bring over there got people's entity so again I saw 3rd just major sticking with the same temperature and your following the ideal gas law but volume is changing commenters that will put the house is a constant often 1st equation so yes so it's it's a director but Ahmed yes each of us specific
substance if you look about anything get a value for yeah so now we're
treating it as a concentrated .period and yet so gazillion point so now I just reading this thing is a constant rate OK so now 1 final problem here so now we've got 2 moles of that expands 80 about equally there were actually figure it out for this 1 2 malls of neon expands about and reverse away from 5 leaders to 20 leaders and were staying at the temperature the unaware that standard after we're starting at the time to 373 Calvin ended some of the temperature so temperatures changing we're not going to use the eyes
of the equation right eye so firms same temperatures is not saying temperature so reiterated
about equation areas so what is there see the value so in this case we had to bring in a statistical mechanics say that you're done not on bring that back in talking about me on which is atomic gas right as far that next concerned we
treat Adams's points right so energy that these Adams have as their bounce around as a gas but you can't rotated .period writers no rotational energy he can vibrate appointee as a vibrational so all we're talking
about is translational suggest refresh your memory if you look at the Hambletonian aghast any of any value that's this squad squared is going to miss a value of are over to write to really get in or over to CD for any value for anything that's quite so happened and the squared of momentum
squared over 2 m both the the squared right so that
those described the Connecticut Energy of the Adams so and we can move in the x y and z direction so we've got 3 tore apart terms so 3 times are over to that's going to be our the capacity for this problem so let's see what I would know everything so we know our initial final volume we know he capacity with melatonin in our change in temperature we have er was often changed their address and it's going to be a 148 Calvin given that they go
fast we will find that that's all I got in the habit questions you're free to go have a good weekend would you have a question the government
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