Physics 27 First Law of Thermodynamics (21 of 22) Summary of the 4 Thermodynamic Processes

welcome to lecture online and in this video we're going to summarize the four thermodynamic processes we have the isobaric process the isovolumetric process the isothermic process and the adiabatic process in the isobaric process pressure is constant in the isov volumetric process volume is constant in the isothermic process temperature is constant in an ad adiabatic process nothing is constant and then we of course have the associated PV diagrams pressure versus volume diagrams and so when a gas expands in in the isobaric process it go straight across notice that the pressure doesn't change in an isov volumetric process the gas cannot expand because it has the volume is constant so by adding heat to the gas gas will simply gain U gain energy and therefore the pressure will increase in an isothermic process the amount of work done by the gas equals the amount of heat it receives in such way that the internal energy doesn't change and so the isothermic process means that it just simply Falls an isotherm the temperature does not change and then finally in an anabatic process it happens so quickly that no energy is received from the outside and so the expansion can only occur if it receives energy from within itself so all the work done is U is accomplished by taking energy from within the gas itself the internal energy so the peculiarity about each of these processes is that in the case of the pressure being constant we know that the work done is equal to the pressure times the change in the volume which also of course is defined right here it's simply the pressure times the change in the volume in the isov volumetric process the peculiarity there as you can see is that the work done is equal to zero because it cannot expand the gas colon do work if the gas expands cannot expand cannot do work in an isothermic process since the temperature doesn't change in the gas the internal energy cannot change so here we can say that Delta U is equal to zero and finally in an adiabatic process it happens so quickly that Q is equal to zero there's no heat added or removed from the gas so Q is equal to Zer so we have for isov volumetric work is zero isothermic change in internal energy is zero and in adiabatic Q is zero and that of course is all related to the first law thermodynamics where it says that the change in internal energy of a gas is equal to the heat added to the gas minus the work done by the gas so in the case of n volumetric process since W is equal to Zer we know that the change in internal energy is simply equal to the heat added to the gas in the case of an isothermic process since Delta U is Zer then we know that therefore that 0 is equal to Q minus W so that means that Q equals W the work done by the gas equals to the heat received by the gas and then finally here we can say since Q is equal to Zer that means that Delta U is equal to minus W or W is equal to minus Delta U and so therefore we can simply find the work done by knowing how much internal energy changes now that's of course a little bit more complicated with tic process because since none of the three variables are constant we have to find the relationship between p v and T in an natic process okay how do we Define the work done in each case well in this case the work done is zero so that's simple enough work is zero in this case the work done can be defined as nrt because T doesn't change that's a constant number times the natural log of the ratio of the volume that you end up with divided by the volume you started with and if those if temperature is not known in this case you can also replace that by P1 * V1 so work done can also be expressed as P1 V1 times the natural log of V2 over V1 or you can say that work done is equal to P2 V2 * the natural log of V2 over V1 so there's a lot of different ways to figure out the work done in an isothermic process the work done in an adamatic process can be defined as the negative of the change in internal energy which can be defined as the number of moles time C subv time the change in temperature which is T1 minus uh T2 minus T1 and of course if those are not known you could also Express the work done as being equal to minus C subv / R time P2 V2 minus P1 V1 so you can find the work done in either way with a natic process the change internal energy is always going to be the same for every uh every I should called thermodynamic process I'm kind of stumbling over my words here but in general the equation always going to be n c subv * delta T so here since pressure is constant that is pretty well the only way you can do that in the case of an isov volumetric process Delta U is equal to q and so we can also say that the Delta U here which is equal to Q which is equal to n c subv delta T and notice that in the case in the case of a isov volumetric process where V is constant Q is also NC of V delta T which is not always the case in an isothermic process uh Delta U is zero so Q is simply equal to the work done so whatever you find out is the equation for work that's also the equation for Q and then here Q is always equal to zero so there we don't have to worry about the heat added to a gas finally um Q here in an isobaric process is a little bit different than there here it is n c subp delta T and notice that c subp is different from C subv so the heat added to a gas is different if it's an isobaric process compared to when it is an isov Vol metric process and don't forget that because sometimes uh you'll have to figure out Q in either an isobaric or an ISO isov volumetric process and it is indeed different so be careful that those are not the same it does depend the heat added to a gas does depend upon how the gas expands or whether or not the gas expands at all so here's a quick little overview that you can always refer to in case you forget how to find W how to find Delta U and how to find q w of course being work in an in a in a thermodynamic process and uh so these are the four main processes that you need to know when you when you study thermodynamics

Channel: Michel van Biezen

Views: 287,449

Keywords: ilectureonline, ilectureonline.com, Mike, Mike van Biezen, van Biezen, ilecture, ilecture online, Physics, Thermodynamics, Specific Heat, Temperature, Pressure, Volume, Heat, Work, Internal Energy, Work Done By the Gas, Heat Added by The Gas, First Law of Thermodynamics, The First Law Of Thermodynamics, Change Of State, Adiabatic Process, Adiabatic, Isobaric, Isovolumetric, Isothermic

Id: AzmXVvxXN70

Length: 6min 46sec (406 seconds)

Published: Thu Jul 25 2013