First Law of Thermodynamics – Chemical Thermodynamics – Chemistry Class 12
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First Law of Thermodynamics – Chemical Thermodynamics – Chemistry Class 12


Do subscribe to Ekeeda Channel and press bell icon to get updates about latest engineering HSC and IIT JEE main and advanced videos Hello Friends now let us learn about what is First law of thermodynamics and what does it states as well as we are going to do the what is the mathematical expression of first law of thermodynamics so let us do it so before understanding what is first law off thermodynamics we should understand what are the statements of the first of thermodynamics so based on the let let us see the first statement which says the total internal energy of an isolated system is constant it is been said that the total internal energy of an isolated system is said to be cost and this means that suppose if we have we have taken a particular system which has been isolated and as you know because of the isolation of that neither of the matter neither the energy can be exchanged with the surrounding or from surrounding to the system so this clearly indicates that since the heat will not be Ott’s in any kind of energy would not interfere with the presence of which is actually present in the system so there would be no change in the internal energy and hence the first law says that there would be no change if we are considering a system which is being isolated it’s a matter of in the means of matter or in the means of energy so the first statement is clearly understood right now so now okay about the next one that is and as you can be converted from one form to another form but it cannot be created or destroyed that is true now it says that energy cannot be created and vo the only thing is we could transform one energy to other form but we cannot create a kind of energy or we cannot destroy a particular energy so that is what the second statement is talking about so now let us learn about what would be the third statement of that so the third statement says that the total energy of the universe is constant yes that is fine because the total energy of the system is a constant because the energy cannot be created as we know and I know she cannot be destroyed so that means that no energy is being created no extra energy has been destroyed so that means the overall energy of the whole universe is said to be constant so even this implies that we are talking about the first law of thermodynamics now let us talk about the last statement that we have with us right now that is the total amount of energy or the total quantity amount of energy of a system and its surrounding must remain constant although may change from one form to wonderful so it clearly indicates that it is talking about the third statement because as we know because universe is basically the energy of the universe we trip in question so for somehow if we are talking about the fourth statement if a pearly amount of energy is been reduced from the system and it has a vent or to the surrounding or it has been evolved in the surrounding and what happens the amount of energy that has been reduced for the system will now be the constant value while that of the surrounding we can see the energy has been increased but the amount of energy that has been decreased in the system is nothing but the amount of energy that has been increased in the surroundings so this clearly indicates the energy is not being destroyed in any case as well as we could see that the energy are constant for both the cases that is for the surrounding and the system overall but yes there would be an exchange with the surrounding and the system the energy would be exchanged from both of them but yes the overall energy would be constant so this is the first law of thermodynamics that we have got to learn now so it is very much clear that what is actually the first of thermodynamics so let me I’ll give you more detail about this thing by giving you a mathematical expression or by giving you a kind of example so that we could get to know that what are we talking about so now let us understand this thing because we know recently that we have studied these statements of the first of thermodynamics and that we have got to know that the first law of thermodynamics is based on principle of conservation of energy just like the principle of conservation of mass the mass cannot be destroyed of mass can be created it will be the same similarly for energy also it is implying the same statement that the for inverse of thermodynamics it is behaving or it is obeying the principle of conservation of energy so let me give you a short example of it again I’ll tell you all right consider a cylinder and close with the gas and having a frictionless movable piston as you could see so this is the gas particles that have been present in the cylinder which has been enclosed through a movable and frictionless piston and talking about the initial state of this when we could see that this gas will have a particular form so that could be considered as B even when that of the particular gas will have an its own internal energy and we know what is internal energy actually it is nothing but the sum up of all the energies that have been present in a system might be rotational energy might be translation energy or any kind of energy it might be kinetic and potential energy that is even present in the system so this clearly indicates that we are going to talk about the internal energy when it is present in the initial state so then the internal energy be human so if I have to provide energy because just now we have made a statement that energy cannot be destroyed or cannot be creativity is equal to be transformed so somehow suppose if I have transferred the heat in this system so what will happen so once I have increased the quantity of heat in the system in this kind of system then what I could see is I could see that because of the internal energy that would have been increased now so that will lead to the increase in volume because when I will heat this kind of system then the collision will start the gas particles will collide with each other and hence the kinetic energy will be more and the kinetic energy will be more so that it will allow more pressure and yes now gets the next one so the gas expands so initially it was it had a volume of human Vivaan but after the expansion the volume will change so that volume will be nothing but video but if the volume changes but if the volume changes then we know that even internals you will have an effect of it because internal energy is said to be a state function and in this case supposing for a pressure and if volume off if any one changes then it is but obvious that internal energy will also have an effect on it and hence so for that instance let me give you a short example and let us see that what I have been done in this case so in this case what we have mentioned is that u 1 is nothing but the initial internal energy why v 1 is the initial volume and in this case Q is the amount of heat that we have provided to the system so therefore Q is equals to what is the heat provided to system something this process what we have observed it as then will be change in volume so the volume will be change to V 2 that is that is the final volume that we loser and if this changes then we know that internal energy will also change so therefore in this process what I have made it as u 2 is nothing but the final internal energy so this is how we have made a statement and we have segregated this terms like u 1 V 1 Q V 2 and u 2 so now now we could easily apply the first of thermodynamics and what it would be let us see now as you know because the internal energy has been changed so now when we are talking about the final internal energy that is when we are talking about YouTube so this final internal energy will be equal to what it we’ll be equal to the internal energy that was present in the initial state as we have provided heat to that so plus Q as well as we could see that the volume has also be changed the volume has been changed from V 1 to V 2 that means the system has performed a bulk and that kind of work can be denoted in this way and talking about the next thing because there is a change there is a change in volume is the work has been done in this process so suppose if the work is done in this process so we could write this equation as u2 minus u1 which is equals to Q plus W but we know that is u2 minus u1 can be denoted as Delta U and in this case Delta U is nothing but the change in internal energy so now this was the change in internal energy that we have observed that is u2 minus V 1 is nothing but the Delta so I could write this equation as Delta U is equals to Q plus W so this implies that if we change the internal energy then there that kind of change in internal energy will be accompanied by two factors that is it will be because of we have provided heat to the system as less in this case when we want that there should be increase in internal energy that means the work should be done on the system by the surrounding so it clearly implies that suppose if we are if we are compressing the piston or if we are making a berth which is based on the compression that means surrounding is acting on the system in that case what happens is the work done is said to be post as well as we could see that we are providing heat also so suppose if we have provided heat to the particular system so in both the cases even if we have provided heat even if we have compressed the piston or if we have performed a birth which is based on compression so in that case the internal energy will be increase so this Delta you will be nothing but the increase in internal energy that we could observe so therefore this Delta u will be increase in internal energy which is equals to Q plus W and this Q is nothing but the heat that we have provided so therefore heat provided to system plus W that is work done on system so if you do this both things on or if we have provide heat or work on the system then there are the chances of the increase in internal energy so this is how this implies the first off thermal means the energy is not being wasted suppose if we have increased the internet seen that internal energy would let us to increase the heat of the system as less to do perform the work by the system so that energy plays a very vital role and this is nothing but the first law of thermodynamics so let me give you another brief example of this thing suppose the internal energy has now been decreased so what will happen so if internal energy is being decreased this is because of the heat is now being moved away from the system to the surrounding as we could see the even if the heat has been expended from the system to the surrounding and if the gas expands so now what we could see is as the work is done by the system to the surroundings so in this case that would lead to the decrease in internal energy so somewhere in terror as you could be very much capable of doing work as well as it could also be used for increasing the heat of the particular system so what are those we are going to study it now so for this instance we have got to know that this is the mathematical expression of first law of thermodynamics in this case the energy has been utilized to perform two things that is – for the heat as well as for work so the both kind of energies are utilized and in this case the change in internal energy is because of the booth that is heat as less the work energy so now suppose if we have implied of some various factors such as what would be the internal energy if we are talking about an isothermal condition adiabatic condition isobaric and isochoric condition so let us talk about each one and let us do a brief analysis that what would be the value of internal energy or what that kind of factors will have effect on the internal energy so talking about the first is suppose if the system or if the system is performing a work of an idea mating process so the system has been performing an adiabatic process then we know that there would be no exchange of heat or there would be no change of heat so heat will remain constant throughout the whole process so in this case basically Q will be is equal to zero so suppose if Q is equal to zero then what would be the internal energy because we know that internal energy that is the change in internal energy is equals to Q plus W and if it is an i adiabatic process means when Q is goes to zero therefore Delta U is equals to W so in this case the W will be positive suppose if we have increased the internal energy making the system to be and performing an adiabatic process then we could see that all the internal energy would be reason for the work done by the surrounding to the system so that means in this case if if we would say if we would do the work on the system by the surroundings so there would be increase in the internal energy and in this case Delta U will be positive so that is what they are telling about so this is a very clear indication that if we want to do work on the system minus then there is the increase in the internet and say that is nothing but delta u so if W is suppose in this case is negative that means it clearly indicates that the system is been performing the work on the surrounding and in this case need anything u that is that would be negative that means it would be case so that is what it was take telling about so net let us do for what will be the case when we are talking about an isothermal condition so when we are talking about an isothermal condition as thermo condition or M say as isothermal process so nice internal process basically there is no change in the temperature as well as the temperature will remain constant for the whole process so therefore delta T is equals to zero so what is actually the role of the temperature in basically in change of internal energy so let me tell you if the temperature is not been exchanged or if the temperature has been kept constant throughout the whole process then what will happen there is will be no kind of exchange of there will be no kind of increase or decrease in the temperature this will let to there would be no change in internal energy and the internal energy would be remain constant throughout the whole process so that means what we are talking about is that is Delta U is equal to Q plus W so because the change in internal energy is because of the heat and because of the work done on the system minus surrounding so since there is no change in the temperature that means it clearly indicates that there would be no change in the internal energy also so in this case what will happen is Delta U will be also zero and if Delta U is zero so this will be Q plus W so therefore Q is equals to minus W we could say in this manner also when we are talking about an isothermal process so what does this Q is goes to minus EE means it means that suppose if we have provided heat to the system that is if we have prevailed plus Q to the system and if the system is performing an isothermal process then what will happen actually the work will be negative this will be negative this work negative indicates that the system will act on the surrounding of by performing a work and yes we and what if suppose if the work is done on the system so if one is done on the system then we could see that the heat will increase and the heat will liberate out and the heat will be of – because if we are to convert the work to be positive obviously the heat will be removed or been expelled from the system so this is what this clearly indicates that if we provide heat then the work done on the surrounding by the system will be more and this is what vice versa when we are talking about Q is equals to minus two P so now let us talk about what would be the case of when we are talking about an isobaric process so in isobaric process as you know that the pressure will remain constant so there will be no change in pressure so therefore in this case pressure is constant I would say in this man so therefore what will be the formula or what will be the change in internal energy that is Delta U is equals to Q plus W that is what we know but we can also write the equation as Q is equals to P Delta V and in this case because the pressure is not being a changing or pressure is been said to be a constant so the heat that we are talking about that is the value of Q it made also remain constant with respect to the pressure so I named it as Q P and this is Delta U so now this clearly indicates that if we want to change the internal energy of the system so that would should be the change in heat that is Q P at constant pressure and the volume it also that she also be changed and but the thing is if you have to increase the internal energy of a previous system then the work should be done on the system by the surroundings so as the work should be the positive one and because of which the heat of the system will also increase and and in a matter of fact internal energy will also increase so this was related to an isobaric process when we are talking about out when we are applying the mathematical expression of first law of thermodynamics in this condition that is an isobaric process so now let us talk about the last section that we have that is isochoric process what will happen in that thing so as we know that in isochoric process we see there is no change in the volume so that for the Delta V will be C so there is no change in volume and if we apply this the first of termina is that we know that Delta usuals to Q plus W but this w can be written as P Delta V because the work is nothing but a pressure won’t work that has been perform and because there is change in volume as we could see as well as we have made an example of that earlier also in deriving the equations like the work done during the expulsion of gas as well as the reversible process in isothermal that is the work doing X function of case so that process what we have got to know that the work is been dependent on the pressure as well as only body and in this case because there is no change in volume as we put C so therefore so this Delta V will be 0 so overall the whole field will be 0 and this is the Delta U so this is but but this is the condition when we see the volume is said to be constant so therefore this equation now will be turned into Delta U is equals to Q V so this clearly indicates that if we are making or if they are keeping the volume of the system to be constant and if you are providing heat so all the heat that we are providing to the system at a constant volume that will increase the internal energy and all those heat energy will be occupied with the or the internal energy will be is will be equal to the in the heat that we have provided to the system so but this will be only possible if we are considering the isochoric process so this there all these systems that we are talking about and all the kind of processes that we have applied on the first law of thermodynamics so thank you friends for watching this video I hope you have liked the student you have understood what is the first of thermodynamics its statements its mathematical expression and its application on the various processes so share this video with your friends and yes don’t forget to subscribe Iger channel thank you so much

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