CLASS-02 | THERMODYNAMICS | TG PCB | TGPSC ASSISTANT SCIENTIST (ANALYST GRADE 2) | BIOGENESIS HYD

Added: 2026-05-09

[00:00:00][snorts] Yes.

[00:00:03]Hello dear students. So we are continuing yesterday's topic. So yesterday we have discussed some basic concepts of thermodynamics that is system and surroundings and boundary surface. Right? So this all will be explained with the help of simple diagram. Any specified portion which is under our observation that is called system. The rest of the part is known as surroundings. Right? So this is the surroundings. Then the system plus surroundings. System plus surroundings that will be universe.

[00:00:43]Right? System plus surroundings will be universe. Right? So whatever is the system we may consider. So that is is present at temperature, pressure and volume. These are the thermodynamic states. So these thermodynamic states do not change with time. So there hence the system will be present at thermodynamic state. If any one of the property will be changed that will be involved in thermodynamic process and various thermodynamic properties are there. So that are somehow intensive properties and extensive properties. Thermodynamic properties that are intensive and extensive. Right? Intensive property extensive property weight dependent.

[00:01:23]Weight dependent is in extensive property. Weight independent is intensive property. So the various properties we are segregated based on that dependent of weight are dependent on number of moles. Somehow extensive and intensive properties and also the ratio of two extensive properties. The ratio of two extensive properties becomes intensive property. Right? So these all will be covered in the previous class. Right? In addition to this we are going to discuss. So one more concept that is about state functions and path functions right supporting state functions state functions and path functions right. So what are the state functions or path functions or we may call as even state properties and path properties right? So two names are there one is state other one is path pathway and state. So depending on the terminology so we can get two different kind of properties. So that will be discussed right. So now here we have to consider one system right. So this is the system A right system A is converted to system B. And this is the system B. So what were the processes involved in this?

[00:02:48]Means the system A is converted to system B through a pathway one. There is a one pathway to conversion of system A to system B. So then other pathways also will be there. So means some other pathway that is pathway number two. Then some other pathway is there pathway number three. Then other pathway also will be there pathway number four. Means conversion of one system to other system. There are many number of pathways are there. Right? So we have to discuss about those pathways. Right? So there are four pathways are there. The system A is converted to system B. But the system A is present at temperature is T1, pressure is P1 and volume is V_sub_1. These are the state variables right? State variables are thermodynamic properties. So the system A is present at T1 temperature, P1 pressure and V_sub_1 volume. This will be converted to system B means B is at temperature is T2, pressure is P2, volume is V_sub_2, right? Any property now we have to consider, right? Any property we have to consider, right? So that is the property that property is depends on depends on. So these are the called as initial states right. So these are the called as final states. Whatever is the property we may consider that is depends on initial states of the system and final states of the system. Initial and final state and independent on independent on right pathways irrespective of pathways.

[00:04:29]How many pathways here? Four pathways are there. So that is independent on pathways and depends on initial states and final states of the system. What is the initial temperature? What is the final temperature? What is the initial pressure? What is the final pressure?

[00:04:45]What is the initial volume? What is the final volume? So therefore the property is set to be state function. Right? So therefore those properties are called as state functions or state properties.

[00:04:57]Right? Any property which is depends on initial states and final states of the system and independent on pathways such functions are called as state functions.

[00:05:08]The example of state functions means right. So these are temperature, pressure, volume are the state functions and all the thermodynamic properties.

[00:05:18]All the thermodynamic properties. What are the all the thermodynamic properties? Means as we discussed internal energy is E. Then enthalpy is H. Entropy is S. Gibbs free energy is G.

[00:05:30]Helmo energy function. These all are thermodynamic properties. All the thermodynamic properties are acts as what? State functions. State functions.

[00:05:39]Remember that this all will be depends on initial states of the system and final states of the system and independent on pathways. There are four pathways are there. Whatever is the pathway we may consider for conversion of system A to system B. So irrespective of that pathways what are the initial and what are the final states that becomes the state functions. These are the examples. Then coming to the path functions right path functions right. So what are the path functions? What are what are the path functions that is quite opposite to the state means whatever is the function we may consider right the function which is depends on depends on pathways.

[00:06:27]How many pathways are there? There are four pathways are there and independent on and independent on initial states and final states of system.

[00:06:46]These are called path functions. Right?

[00:06:49]So state functions are dependent on initial and final states independent on pathways. Right? Coming to the part of path functions. These path functions are depends on pathways and independent on initial and final states. Right? So there are two path functions are there.

[00:07:07]Right? Example of path functions. One will be heat. The other will be work.

[00:07:13]Heat will be denoted with Q. Work will be denoted with W.

[00:07:18]These are the two path functions. These are the thermodynamic properties or state functions. Now we are going to get the relation between all the thermodynamic properties and state and path functions right. So between the state functions and path functions are all thermodynamic properties and path properties. So that is called thermodynamics.

[00:07:41]Right? So in further what we are going to getting the information regarding these functions means we have some thermodynamic properties. How this thermodynamic properties will be changes with respect to the pathways right? How we each which which will be depends on path means for example heat is there right as I said earlier heat is either observed or heat is released right. So whatever is for example in this case heat is released right. How much amount of heat is released through pathway one?

[00:08:13]That may not be same in pathway two.

[00:08:17]In both situation, both pathways means pathway 1 2 3 4 some heat will be released that heat may not be same.

[00:08:25]Hence that is depending on pathways that is depending on pathways right and independent on initial and final states.

[00:08:33]Whatever is the initial and final states will be there. So that properties are depends on only pathways and also work.

[00:08:40]For example in this pathway some work done will be there pathway one that work done may not be equal with other pathways. So hence these two are depends on pathways only the just path functions means you have to remember heat and work are the path functions. Remaining all thermodynamic properties are what state functions right? So here just remember that state functions are depends on initial states and final states independent on pathways. Path functions means depends on pathways independent on initial and final states. Right? So this we may explain with the help of an example. Right? So these all are what state functions and path functions.

[00:09:21]Right? How the state functions and path functions are independent on pathways and dependent on initial and final states. Right? If you may consider one example, right? Integral of ds, right? D means nothing but change of entropy. S is entropy. Right? We have initial state is initial state to final states. Not mentioning whether that may be temperature or pressure or volume.

[00:09:48]Right? So this initial to final. Now this will be integral of initial state 2 which will be following a pathway X whatever is the X value right. So one pathway will be there x pathway of ds plus integral of x pathway to final state integral ds means initial state to final state there is one pathway is there what is the pathway here followed by x x is a pathway anything we have to consider in this x we'll get some result right now the same ds in change in entropy initial state is there final state is there.

[00:10:30]This will be now it may depends on right initial state to pathway will be y into ds plus integral of pathway is y to final state right y to final state into ds here the pathway will be x here the pathway will be y right just I am indicating those pathways right initial state two what about the pathway here follows x then initial state two what about the pathway way here follows Y right. So Y pathway will be there then X pathways different pathways are there whenever we may get that integration part of this function. So both are giving same value only both are giving same result.

[00:11:17]Hence, hence this is the function ds is does not depends on pathways. Whether we may follow pathway x or we may follow pathway y the overall result will be same because that is depends on initial and final state only. What are the initial? What are the final? What are the initial? What are the final? So hence these properties are called as what? State properties right or state functions right? State functions.

[00:11:45]Similarly we may consider right so one of the path property. So we know that Q and W are the path properties right. So therefore integral of DW then initial state to final state. Initial state to final state. So here we may follows one pathway that is initial state to pathway x of dw plus then integral of x2 final state of pathway dw. Here we will get some result right. So means we have to follow one pathway that is the x. In other case, so the pathway will be changed that is integral of initial state to final state of dw that is equals to integral of initial state to now here pathway will be y dw plus integral of y to final state of dw.

[00:12:42]What here we have changed the pathway will be changes here. What about pathway? X is a pathway. Here what about pathway? Y is a pathway. Whenever pathway will be changes the obtained values right different result will get different result we will get we are not getting same result because pathway will be different means this is a function dw is depends on pathway w is a work function that is depends on pathways hence we are getting different result therefore this we may call as path function right see how it will be Here any property you have to consider in both the cases we have changes pathways right. So here we have changes pathways. So therefore we are getting same result means that is depend on initial and final states and independent on pathways. This is state functions are what? Independent on pathways. Right?

[00:13:41]Independent on pathways.

[00:13:45]Pathways whether we may change the pathway we are getting same result only.

[00:13:49]But here whenever we change a pathway so this is dependent pathways are dependent on pathways. Path functions will be depends on pathways only remember that two path functions are there heat and work. The remaining all thermodynamic properties are state functions. What is the relation between them that we are going to discuss in our thermodynamic whatever they mentioned syllabus right that we are going to explain with the help of these functions state functions and path functions all thermodynamic properties are becomes what state functions right so then heat and work will be path function whatever the relation between these means how the heat energy will be exchanged between the system to surroundings what will be What will be the change of internal energy, change of enthalpy, change of entropy, change of uh gibs free energy, change of hely function? All information we will get right. So this is about regarding state functions and path functions. Right? So in addition to this in addition to this some terminology is there means so some terms are there in our thermodynamics definitely we have to understand the terms with the help of that we can understand the further subject easily right so means so we know that right now we are in hot condition temperature will be very high so therefore we have to discuss about heat is denoted with Q Right? Heat. So simple thing how we have to define that heat.

[00:15:26]Heat is added form of energy or disordered form of energy. Simple thing hot water temperature surroundings in all 360° temperature will be transferred means there is no particular order. There is no particular order.

[00:15:49]Hence heat energy is a what? Disordered form of energy. Right? So that we have to remember first. Heat is a it is a disordered form of energy. It is disordered form of energy.

[00:16:09]Disordered form of energy. Heat is what?

[00:16:11]Disordered form of energy. Right? So what is meant by heat definition?

[00:16:19]Right. The energy whatever is energy which is exchanged the energy which is exchanged between system and surroundings. system and surroundings surroundings due to due to temperature difference.

[00:16:43]Due to temperature difference that is called heat. Means energy exchange will be taking place between the system and surroundings. That exchange of energy will be with respect to what? Change in temperature. Change in temperature.

[00:17:00]Right? So here we consider one terminology that is the system and surroundings all those things. Right? So this is the any specified portion which is under our observation that is called system. The remaining part is what?

[00:17:12]surroundings, right? This is the surroundings. This is the surroundings and here surroundings, right? System is there and surroundings is there. Now, we have to apply the three conditions, right? So, what are those three conditions means? Right? So, the condition number one, right? If temperature of the system is greater than temperature of the surroundings system to surroundings, surroundings to systemcat is transferred from weight where high temperature to low temperature is automatically Right.

[00:18:11]Yes. Surroundings is gaining energy.

[00:18:14]Right? So here surrounding is gaining.

[00:18:17]When surrounding is gaining, right? What about the system? S system is losing.

[00:18:26]Losing energy, right? So therefore whenever temperature of the system will be more temperature of the system will be more system lost some amount of energy. System lost some energy.

[00:18:41]Whenever system lost some energy that will be denoted with what? Negative.

[00:18:48]System will be lost some amount of energy when system temperature will be more. Right. Right. So the second condition is there. The temperature of the system right the temperature of the system is less than of temperature of the surroundings.

[00:19:15]From high temperature to low temperature high temperature to low temperature and this is the condition one. What about this system to surroundings this is the condition number two surroundings heat energy absorb system absorb mean system is gaining right. So hence system is absorbing absorbing some energy some energy right some heat energy or energy right when system is gaining means therefore Q is equals to what positive when Q is heat energy is positive it is a heat only heat is what denoted with Q when Q is positive Q is negative this we have to understand clearly Right. So gaining and losing temperature difference where parameters effect only that is due to temperature difference then only we may consider as heat energy. So that's why I mentioned that exchange of energy exchange of energy energy exchange between the system and surroundings that is due to temperature difference only temperature difference. So rendered temperature same that is the third condition right. So for example temperature of the system will be equals to temperature of the surroundings.

[00:20:48]Both the temperature will be same when temperature of the system is equals to temperature of the surroundings.

[00:20:54]Therefore, there is no exchange of heat energy between the system and surroundings. No exchange of no exchange of heat energy. No exchange of heat energy. That is the process we may consider as thermal equilibrium. Thermal equilibrium condition thermal equilibrium systems right or else one system is thermally equilibrium with surroundings systeming temperature will be same right for example water at 100° centigrade.

[00:21:44]Environmental temperature is 27° centigrade. Now in summer hot condition it little bit it will be approximately 40 around. Right? But generally we may consider room temperature is 25 or 27° centigrade. Right? So hot condition means 100° centigrade surrounding will be 27. Some amount of heat energy is transferred to the surroundings.

[00:22:07]Whenever system is going to lose the moment of energy, so that will be denoted with Q is negative.

[00:22:17]When both the temperatures should be same, inside and outside temperature same.

[00:22:33]temperature equilibrium exchange of energy. So therefore hence that equilibrium is particularly known as what thermal equilibrium based on this thermal equilibrium condition we are going to explain zero law of thermodynamics.

[00:22:51]What is meant by zero law of thermodynamics? That will be explained with the help of this conditions only.

[00:22:56]Third condition only. Clearly remember first condition means temperature of the system will be more then compared to surroundings at the time systems losing some amount of energy to the surroundings. Right? So some amount of energy will be giving to the surroundings. System will be losing means hence that will be denoted with Q is negative. Second situation surroundings temperature will be more system right. So when system is gaining some amount of heat energy from the surroundings right at the time Q is positive right temperature there is no exchange of energy thermal equilibrium thermal equilibrium concept zero right so this is about heat energy and what are the units of heat what are the units of heat right so heat will be expressed in units, right? Particularly in physical chemistry definitely we have to identify the units whenever you are doing the questions particularly physical chemistry questions right. So next options option questiont but unit conversion is very important right. So same options options.

[00:25:05]calories. So there is a very important thing. So we have to focus on the unit conversion. Right? So I will explain some parameters are there. What are the units? How the relation between all those units unit conversions also I will explain in detail. Right? Therefore, units of heat energy is J right. Next, calories. Next, eggs, right? Jles, calories, eggs. Next, kilojles. Kilo calories, right? Kilo x K for kilo. These all are units of heat energy. Heat difference.

[00:25:46]Temperature difference.

[00:25:53]No exchange of energy. As here we discussed whenever the temperatures are same there is no exchange of energy.

[00:26:01]There is no exchange of energy. Whenever temperature difference is there. So that's why heat is a disordered form of energy. It is exchange between the system and surroundings. That is due to temperature difference. That is called heat energy. Right? That is called heat energy. Right? So then coming to the part of one more parameter that is called work. Right? So these are the units. Right? Then this is very very important of terminology that is work.

[00:26:34]Very simple right.

[00:26:45]So I have done some work.

[00:26:57]Yeah. Right. So to displacement of any object with help of application of external force that is called mechanical work. Right. So definition right. So that is a work. Work is a ordered form of energy.

[00:27:28]ordered form of energy and sequence ordered form. Right? So ordered form of energy, right? What is the ordered form of energy? Similar to the definition of heat energy, right? It is a form of energy. Which form? Ordered form of energy? It exchange between exchange between Exchange between system and surroundings. It is exchange between system and surroundings due to due to other than temperature difference.

[00:28:10]Other than temperature difference, right? Other than temperature difference.

[00:28:19]Temperature difference.

[00:28:21]Temperature difference.

[00:28:39]Due to difference in pressure that is due to difference in pressure other than the temperature means what we have considered pressure difference is there right. So similarly similarly we will go with the diagram right. So there is a system is there right? So this is the system it has surroundings right.

[00:29:08]Okay.

[00:29:20]Right. So what are those three conditions? We'll see. Right. So the first condition will be pressure of the system. Pressure of the system is greater than pressure of surroundings.

[00:29:32]Right? Pressure of the system is greater than pressure of surroundings.

[00:29:37]Simple thing high pressure region to low pressure region and system pressure will be transferred means whatever the system system is gaining or losing Right? So system is giving some pressure to the surroundings means system is doing some work. So that can be denoted with whenever pressure of system will be more. Therefore that is work done work done by the system. Work done by the system.

[00:30:30]Work done by the system on surroundings.

[00:30:36]There is a work done by the system on surroundings. Right? So whenever the pressure of the system will be more system so it will be lose work done by the system means hence w is equals to denoted with negative. Whenever work done by the system that becomes w is negative right. So the second condition is there right? So what about that second condition?

[00:31:09]Now pressure of the system pressure of the system is less than our pressure of the surroundings.

[00:31:16]conditionings to system. Right? The pressure will be moving from surroundings to system.

[00:31:30]That is that pressure in terms of expressing in terms of work. Right?

[00:31:39]Right. Work done by the system on the surroundings.

[00:31:47]work done by the surroundings on the system. Therefore, what is the terminology? We'll get work done work done by the work done by the surroundings.

[00:32:00]Work done by the surroundings on the system.

[00:32:09]Yes, the system is gaining energy. When the system is gaining energy that is W is equals to negated with what positive system is gaining energy right so one is the condition is pressure of the system will be more therefore surroundings pressure will be less there is a work done by the system on the surroundings terminology is very important right work done by the system work done by you right so work done by you means you are doing work like work done by the system system is going to do work. So on the surroundings at the time system is going to lose some mount of energy. Hence W is equals to negative. Then next surroundings where there will be more.

[00:32:55]Therefore surroundings are doing some work on the system work done by the surroundings on the system at the time W is equals to positive. Right? Coming to the part of third condition. Right? So as we discussed previously pressure of the system is equals to pressure of external. Pressure of the system is equals to pressure of external means. So there external part is what?

[00:33:18]Surroundings. Here we have to discuss right. Pressure of the system is equals to pressure of the surroundings. As there is a work done. Rend pressure same. Therefore no work done. No work done.

[00:33:35]There is no work done.

[00:33:41]Mechanical equilibrium presum right there is no work and means therefore W may be considered as zero.

[00:34:04]When W is negative, W is positive. When W is zero. So that is depending on the pressure. Right? So depending on the pressure means how the work will be depending on the pressure. So how we are going to define the work then what are the units of work? We have to know in detail about heat and work then only which will be correlated with the thermodynamic properties like internal energy, enthalpy, gs of free energy, helmo energy function and uh entropy.

[00:34:35]Right? From that only we will get whatever the topics mentioned in our syllabus. So that all the topics will be understood easily if you understand this concept. Right? So is it clear? Right?

[00:34:47]This is the work. Work will be denoted with W. Simple thing. This entire concept will be explained or done with only this simple diagram. Right?

[00:34:58]Previously heat energy also will be same. Therefore, it is the work is the ordered form of energy. Ordered form of energy. Right? So therefore the units of work is work is a energy form. Same units are applicable. Jels, calories, eggs, right? So then kilojles, kilojles, kilo calories, then kilo eggs. These all are units. Even even work units also will be mentioned that is literosphere also. Literosphere also units of work that we may particularly work also we may call as pressure volume work. Right?

[00:35:42]So later on in the next classes we will get whenever we are going to discuss about work means that is what pressure volume work how we are getting that relation between the work and pressure with respect to the volume. So that we will see right these are the units which will be applicable and uh what is the condition we will get here mechanical equilibrium we'll get in case of heat energy what we'll get thermal equilibrium we'll get thermal equilibrium same explanation zero law of thermodynamics explanation right then what is actual work right so then what is the actual work means mechanical work that we have to define right So work or mechanical work. So W work can be denoted with W. W is equals to force is multiplied with the displacement.

[00:36:39]Force is multiplied with displacement.

[00:36:43]To displace any object from their original place to other place, what we have to do? We have to apply some external force with the help of application of external force the object will be displacement. So how much distance it will be displaced that will be multiplied with force that can give the work right. So therefore W is equals to force into displacement. The force will be F displacement small displacement that will be DL. Therefore this is the W. Right? So then now any object posess some area that's why that force will be divided with area and multiplied with area and multiplied with the dl F into DL area get cancel therefore we will get again F into DL only means by multiplying and dividing with area there is no change in the value that is F into DL right so then many times we feel pressure what is the pressure means that is the definition that is force per unit area. Whatever is the force which is applied on unit area that is called pressure. Right? So therefore W is equals to pressure into area into length. What about area into length?

[00:37:59]Volume. Therefore small length is there that's why small volume. So therefore this is W is equals to P DV. We have to write W is equals to P DV. Whatever is the this pressure that is applicable for system, right? The pressure that is applicable for system. Therefore, pressure of system is equals to force per unit area. If area is equals to 1 cm²ared, area is equals to 1 cm²ared. Right? 1 cm²ared.

[00:38:31]Therefore, P is equals to F. The corresponding force is equals to pressure. Means whatever the force we have applied on particular unit area that may be even me square also we may consider so that force will be equals to pressure.

[00:38:48]This force and pressure will be applicable for the system right. So whenever system pressure for example for example if you may consider system then here is the surroundings right system pressure is in this direction means the surroundings pressure will be in opposite direction right. So for example system pressure will be this direction.

[00:39:09]The surroundings pressure will be in opposite direction. Both system and surroundings are opposite directions.

[00:39:16]Hence this P will be equals to external pressure. If outside pressure we have to write that becomes minus. If it is plus that becomes minus this is P means P of the system is equals to minus P external. Therefore W is equals to minus P into DV. We have to write. So, so D means a small displacement. If it is a large displacement is there, therefore W is equals to minus P into delta V. Delta is applicable for the large displacement. So then pressure and volume will be there. So these relations will give the work. That's why we called as pressure volume work. Previously I told that pressure volume work. Pressure volume work. Right? So that is called work. Right? Work and heat are the what?

[00:40:05]State functions. Work and sorry work and heat are the path functions. Work and heat are the path functions. How these path functions are related to the various state functions. So that will give huge information regarding our processes. Right? So therefore what we have to remember the work means we have to remember W is equals to PDV. So when external pressure we may use. So the direction of external pressure will be opposite to the system. Therefore, hence that will be minus p external into dv minus p external into dv or minus p external into delta v minus p external into delta v. Therefore simply we may call as w is equals to p dv right. So in all our heat and work so what we are going to get the information right. So what we are understand that information means right simple thing so that we may write in the note right simple thing first one heat is heat is observed the if the system heat is observed so what is the symbol Q is equals to observed means Q is equals to positive right heat is Heat is released.

[00:41:29]Heat is released. What about the Q? Q is equals to negative. Heat is released means Q is negative. Heat is observed means Q is gaining means positive.

[00:41:41]Right? Heat is observed Q is positive.

[00:41:43]Heat is released that is Q is negative.

[00:41:46]Right? So the second one is work done.

[00:41:50]Work done by the system. Work done by the system on the surroundings. Right? Work done by the system on surroundings. Work done by the system means what about the W? W is equals to negative. So then next work done.

[00:42:08]Work done by the surroundings. Work done by the surroundings on system on the system. So system is gaining some amount of energy that becomes positive. Right?

[00:42:21]So these are the terminology we have to remember right. What is the relation between the heat and work? If it heat is observed Q is positive. If heat is released Q is negative. If work done by the system W is negative. Work done on the system W is equals to positive.

[00:42:39]Right? So when when Q is negative Q is positive. When W is negative W is positive. Based on this terminology we will get some questions. Right? Whatever the question will be mentioned just we have to find out the internal energy of the system when some amount of heat is observed and some work done will be done by the system. It is observed means Q we have to consider positive work done by the system means W we have to consider negative. So these two will be substituted in first law of thermodynamics. Therefore we can get internal energy also. Right? So these are the first two work and heat energy.

[00:43:20]So with the help of these somehow other parameters we are going to discuss right. So what are the other parameters means internal energy slowly we are entering to the our main topics right internal energy right?

[00:43:42]Internal energy.

[00:43:45]So this is denoted with E or in some books it is denoted with EU right any symbol we have to utilize internal energy is E or U also consider right you also internal energy right so what is meant by internal energy what is meant by internal energy right so simple definition the energy which is exchanged are the energy which is present in the system.

[00:44:22]The energy which is present in the system present in the system at a constant volume.

[00:44:34]Whatever is the energy which will be present in the system at a constant volume that will be considered as internal energy. What is meant by internal energy? Means it is a energy.

[00:44:46]It is energy which is present in the system.

[00:45:00]Energy means the sum of the sum of all the energies. The sum of all the energies.

[00:45:18]The sum of all the energies present in the system.

[00:45:25]All the energies.

[00:45:27]All the energies. So therefore internal energy is equals to sum of potential energy plus sum of kinetic means the sum of potential energy and kinetic energy.

[00:45:40]Right? Potential energyinetic energy internal energy system is having energy internally that is called internal energy or the sum of all the energies which are present in the system that are potential energy and kindinetic energy. This kinetic energy may be right. Kinetic energy may be translational energy, rotational energy, vibrational energy, then electronic energy. The sum of all these energies becomes considered as what? Internal energy. This internal energy is denoted with E or U. Internal energy is denoted with E or U. Right? So see here, right?

[00:46:28]Right. This is then units of energy as we discussed energy units are about jewels, calories, then kilojles then kilo calories etc. These are the units.

[00:46:42]These all are forms of energies energy units are same only. So but unit conversions must remember right. So these are the units for internal energy right. So how we are going to explain the internal energy right? So with the help of consideration of system right. So that will be C right. So here one system is there. So that will be with the help of first law of thermodynamics also at the time again I will explain right. The system is going to absorb some amount of heat energy that is Q system is going to absorb.

[00:47:25]So whenever heat is absorbed the system is going to do work. The system is going to do work. Heat absorb right. So some of the amount of energy is utilizes to do work. The remaining rest energy is present in the system that is in the form of internal energy.

[00:47:48]Whatever is the rest of the energy which is present in the system that is called internal energy. That internal energy may be sum of potential energy and kinetic energy or that may be T means translational energy, rotational, vibrational and electronic energies.

[00:48:05]Electronic energies right. So here internal energy is E right. So therefore, so here we have to remember like internal energy E is exactly the exact the exact value of exact value of internal energy E cannot be determined cannot be determined.

[00:48:37]Then what we have to determine the internal energy means E or U that cannot be determined means what we have to determine means whenever the system and surroundings are there. What is the exchange of energy between them that is happened at constant volume that is considered as change of internal energy.

[00:48:58]The exact value or absolute value of internal energy cannot be determined.

[00:49:03]But what we have to determine the change of the change of the change of internal energy can be determined can be determined.

[00:49:18]What we have to determine the change of internal energy. So therefore what we have to say here the internal energy the internal energy we cannot determine but what we have to determine the change of internal energy we can determine right energy exchange between the system and will be taking place this energy exchange change between the system and surroundings at a constant volume that energy will be equals to change in internal energy. Right? So simple thing not only internal energy any thermodynamic property is there the absolute values we cannot determine except entropy exception [clears throat] on the entropy absolute values of entropy can be determined with the help of third law of thermodynamics but but the remaining all thermody properties exact or absolute value we cannot be determined with similar to this right similar to this we cannot determine we cannot determine g we cannot cannot determine uh h enthalpy. We cannot determine a these absolute values we cannot determine. But what we have to determine the change of gibs of energy, change of enthalpy, change of internal energy, this can be determined, right? But in case of entropy, in case of entropy, the absolute values of entropies also can be determined. Whenever absolute will be there, the change of entropy also can be determined. So this is we have to keep it in mind. So right this is the most important term. So that is what the exact value is nothing but absolute values. The absolute values of internal energy cannot be determined but the change of internal energy can be determined. So for measurement of internal energy so one experiment is there that is also we are going to discuss that is what bomb calorie meter with the with the help of bomb calorieter we can get the internal energy right that is particularly change of internal energy so this is about concept of internal energy right so then we'll see based on that internal energy so the type of reactions also we may explain right so delta we have to define delta E. This we have to define.

[00:51:48]What is meant by delta E right? So delta E means change in internal energy.

[00:51:56]Right? So this is the energy exchange.

[00:52:00]This is the energy exchange between system and surroundings. between system and surroundings at constant at constant volume.

[00:52:15]So that is called change in internal energy that is called change in internal energy. Right? So therefore delta E can be delta E can be written as heat energy that is exchange exchange of heat energy at constant volume. Exchange of heat energy at constant volume. Right? So this is the heat at constant volume.

[00:52:42]Heat at constant volume that is called change of internal energy that is called change of internal energy.

[00:52:55]Heat of reaction at a constant volume that is change of internal energy that will be equals to QV. Right? Heat is the what? That is due to temperature difference. The exchange of heat energy between the system and ceronics due to temperature difference. So that will be considered as delta E. That will be considered as delta E. If this delta E will be positive or delta E will be negative. So the what will happen that we are going to apply for a reactions.

[00:53:23]For example, any reaction is there reactants which are gives rise to products. Right? This is a general reaction. General reaction.

[00:53:34]General reaction. Reactants are gives rise to products. Reactants are gives rise to products.

[00:53:50]So that will be first one. Reactants are absorbing some amount of heat energy then converted to products.

[00:53:58]Right? React energy 20 kilo 20 reactant 20 plus 30 by giving 10 J of energy to the reactants we can get the products right so therefore how we'll get for this reaction delta E Means delta E means energy of products minus energy of reactants. Energy of products minus energy of reactants. How we'll get the change of energy? Energy change in a general reaction catalyst. Product energy minus reactant energy. What is the product energy here? Right? So product energy is 30 J. Product energy is 30 J. 30 J minus reactant energy and 20 J. Right? So 20 30US 20 how much? 10.

[00:55:07]Delta is equals to Q1. Delta is equals to Q. This is when volume will be kept constant.

[00:55:17]Delta A will be QV. Right? So here delta is equals to QV means heat at a constant volume. at constant volume QV that is 10 joules. Delta A will be 10 joules.

[00:55:30]Right? So therefore delta E is equals to QV. Right? So this is the change of internal energy. Whenever heat energy is observed hence that reaction is called as what? Ex endothermic reaction.

[00:55:44]Endothermic reaction. For endothermic reaction delta E will be what we have to consider that will be positive. This is also we have to remember for endothermic reaction delta E will be positive and delta E is equals to QV. All these terminology we have to utilize right.

[00:56:02]Okay. Next one more condition I am taking that is the second condition. The reactants which are converted to products by releasing some amount of heat energy. That is the second condition. Right?

[00:56:15]That is the condition is what? Second condition. Right? So therefore here reactant energy will be 30 J. How much reactant energy? 30 J. Right? So then here product will be 20 J. Then heat will be how much it will be released? 10 J. Right? How much energy will be released? That is 10 J. Therefore here the change of internal energy delta is equals to E of products minus E of reactants. E of products is what? 10 Joules minus E of reactant is 30 J.

[00:56:50]Therefore what we are getting - 10 J. So here heat is released means that we may have written as negative. Therefore this negative indicating what released negative indicating released then the released energy will be tou here will be toules. Therefore delta E is negative.

[00:57:10]Delta E is negative. That means such a process is known as what? Exothermic process. Exothermic process.

[00:57:20]Right? Whenever delta is positive that becomes endothermic process. Delta is negative means exothermic process.

[00:57:28]Right? So that is in terms of internal energy. This is the concept of internal energy. Internal energy. Right? Similar to this we have to explain about the enthalpy also. Right? So same conditions that will be applicable for enthalpy also. But how we have to define that enthalpy right? So that will be C right.

[00:57:51]So with the help of enthalpy we able to get first law and the second law of thermodynamics equations right. Okay.

[00:58:00]Right. So that is enthalpy.

[00:58:04]This is a concept is very important of enthalpy. Enthalpy is denoted with the H capital H. This is also called as heat content of the reaction. Heat content of the reaction. Heat content of the reaction.

[00:58:24]Right? How we are going to define this enthalpy of the reaction? So that is in terms of that is in terms of internal energy, right? So whatever is the internal energy is there, right? So H will be defined as right we have to remember this equation. H will be defined as internal energy plus PV. This PV is what? Pressure volume work. Right?

[00:58:51]Means heat content. H is the what? Heat content. Heat content of the system.

[00:58:56]Right? So that here I will explain.

[00:58:59]Right? So system is there. The system is going to absorb some moment of heat energy that is Q. Then this is going to do work. The rest will be present in the form of internal energy. What is meant by first law of thermodynamics means the sum of internal energy and work which is equals to how much amount of heat energy is observed by the system. How much amount of heat energy is observed by the system? That is called first law of thermodynamics. So we will discuss again internal energy will be E. Then uh E Q is equals to Q is equals to internal energy plus W.

[00:59:42]Q is equals to internal energy plus oh sorry internal energy is equals to Q + W we have to consider right means whatever is the internal energy is there that is also we have to consider but approaching will be different only right internal energy whatever is the internal energy is there that will be how much amount of it is observed and how much work done will be there the sum of that two will be equals to what internal energy. So therefore, hence internal energy E is equals to what? We have to write Q + W. Internal energy is equals to Q + W. That is the formula first law of thermodynamics, right? Means means what we are considering here C Q is the heat right this Q will be equals to internal energy. So when pressure volume work will be there the sum of this internal energy and pressure volume work right. So this will be the pressure will be already we know P is equals to work done by the system means minus P DV.

[01:00:46]Therefore E is equals to Q minus P DV.

[01:00:49]We have to write E + P DV is equals to Q. This Q is nothing but the heat content of the system that is the enthalpy right. So that we are going to define here right. So means enthalpy H is the internal energy plus pressure volume work. The sum of these two right internal energy and pressure volume work these two will be equals to what heat content of the system that is called enthalpy right E is a internal energy this is internal energy then H is a enthalpy H is a enthalpy H is equals to E plus PV right if you may consider if you may consider at constant pressure at a constant pressure Right? At constant pressure. Right? So what is meant by that? Delta H is equals to delta E plus constant pressure means P delta V. We'll get delta H is equals to delta E plus P delta V. Right? At constant pressure. So this is UV method. P delta V and V delta P we will get. So at constant pressure delta P will be equals to zero. Hence the second term will be zero. Therefore we will get the relation is delta H is equals to delta A plus P delta V. Right?

[01:02:11]So delta H is change in enthalpy. What about enthalpy? H only as I said previously H is the absolute value that cannot be determined. But what we have to determine delta H only can be determined.

[01:02:27]Delta H only can be determined. What is meant by delta H? means change in internal energy plus pressure volume work. So the sum of these two will be equals to delta H. Right? So hence we are going to define delta H also. Right?

[01:02:44]Delta H. I will define delta H means it is the energy. It is the energy exchange between exchange between system and surroundings. system and surroundings.

[01:03:00]It is a energy exchange between system and surroundings right at constant at constant pressure right. So simply we have to written as delta H is equals to QP.

[01:03:17]Q is a heat energy which is exchanged at where at constant pressure. At a constant volume will be internal energy at constant pressure will be enthalpy.

[01:03:27]This we have to remember. So therefore heat it is heat of reaction. Heat of reaction at constant pressure. Heat of reaction at a constant pressure. That is known as what? Enthalpy. Change of enthalpy. Right. So there is a one instrument experiment is there to measure the delta E and delta H both. So that is bomb calorimeter and water calorimeter or else. So type one calorimeter and type two calorimeter two different kind of calorimeters are there that calorimeters are required to get required to get the change of internal energy and enthalpy of the systems. The change of internal energy and enthalpy of the systems right. So then here similarly which is applicable for enthalpy also energy only. Therefore the units are same applicable and how it will be applicable for the reactions with the help of this we are going to get exothermic phenomenon and endothermic phenomenon. So as you know that for exothermic what about the change of delta E and delta H right similarly similarly for a general reaction for a general reaction right the reactants are gives rise toward products therefore the change of enthalpy delta H can be HP minus HR that means enthalpy of products minus enthalpy of reactants enthalpy of products minus enthalpy of reactants right so By considering one reaction the reactants by absorbing some amount of heat energy then converted to products.

[01:05:08]So therefore this is uh 25 J right 25 J this is 10 J then product will be 35 J right. Therefore delta H will be what? H of products minus H of reactants. H of products is 35 minus 25 that becomes 10 J. These 10 jaws will be equals to absorbing heat energy. This entire process is carried out at a constant pressure only. So therefore, hence delta H is equals to Q of P. Right? So therefore here positive sign we are getting. So hence delta H is equals to positive. So this is the reaction is known as endothermic reaction as similar to delta E. This is endothermic reaction. Right? Endothermic reaction.

[01:06:00]Endothermic reaction. Similarly, so the reaction will be carried out with the liberation of some amount of heat energy. Right? So that means other kind of reaction reactants are gives rise to products by liberation of some amount of heat energy. So for example here 35 joules of heat energy is there 25 joules of products then 10 jewels of heat energy is liberated. Therefore delta H can be written as right H of products minus H of reactants that is 25 minus 35 that becomes - 10 J this minus is a releasing therefore which will be 10 J will be equals to Q so therefore hence in this case also delta H is equals to Q of P right the exchange of heat energy between the system and surroundings are between the reactants and products so that is at constant pressure That will be considered as change of enthalpy. But here negative we are getting delta H is equals to negative. So therefore such reaction is what? Exothermic reaction.

[01:07:06]Exothermic reaction. So this is about what? Delta H as similar to the delta E. Delta H also how it will be correlated with heat energy. As I said state functions are relation with the path functions. H and E are the state functions. How that will be correlating with path functions of heat energy. Next we have to correlate with the work done also. Right? So therefore this is the delta H is negative delta H is positive. Right? So hence the equation will be delta H is equals to delta E plus P delta V. So that is also from that we will get some more equations. Right? So from that we will get some relations also. How it will be related to that we'll see right.

[01:07:52]So that is we know that delta h is equals to delta e + p delta v. delta h is equals to delta e + p delta v that we know that we know that right. So then from ideal gas equation from ideal gas equation we know that ideal gas PV is equals to RT this is applicable for 1 mole for N mole PV is equals to NRT PV is equals to NRT this is applicable for N mole 1 mole K RT N moles means NRT right at a constant pressure at constant Pressure pressure constant volume will be changes number of moles will be changes when temperature is constant or when pressure is changes when pressure is constant volume is changes number of moles are constant gas constant then temperature will be changed right so therefore P is equals to what we have to consider either delta N RT R NR delta T here number of moles will be constant therefore change in temperature considered here temperature is constant number of moles will be changes right so so many ideal gas equations are there that we will explain with the help of thermodynamic processes right so what is meant by thermodynamic process at the time we will get so these will be substituted in above equation so therefore we will get delta h is equals to delta e plus delta n rt Therefore we can get the relation between delta H and delta E.

[01:09:42]How delta H and delta E will be related with each other. Right? If delta N is zero. Right? So there one case delta N is zero. When delta N is zero means this entire term will be zero. Hence delta H is equals to delta E. Right? If delta N is equals to positive. Right? If delta n is positive. So this is the positive value means for this delta E we are adding some value then only it will be equals to delta H means right delta H is greater than delta E right if delta N is equals to negative right so negative delta H is less than delta E right so these are the relations between delta H and delta E we'll get right delta H and delta E relations we will get like that use conversions are there simple thing.

[01:10:42]So one concept to other concept means It is the connectivity topic only last right. So therefore this is the equation we have to remember if any reaction will be there then how to consider delta n right so I will explain consideration of delta n with that I will conclude and we will discuss some numericals based on this right. So that is delta n will be number of moles of number of moles of gaseous products.

[01:11:32]Number of moles of gaseous products minus number of moles of moles of gaseous reactants.

[01:11:44]Number of moles of gaseous reactants.

[01:11:47]Right? So number of moles of gases products then number of moles of gases reactants means delta n canb is applicable for only gases. If solid is there liquid is there right? So we want to consider that will be applicable for what only gases particularly gases are involved in the reaction. So therefore delta n can be we can get right. So that uh we'll explain with one example and uh we'll conclude that right. So relation between delta E and delta H for the following reaction right so what is the example right we'll see dissociation of HI dissociation of HI that means 2 moles of HI is dissociates into H2 molecule plus I2 molecule this HI will be gas H2 will be gas then I2 will be gas okay right first what we have to consider delta N number of moles of products.

[01:12:48]What about number of moles of products?

[01:12:50]Here 1 mole is there. Here 1 mole is there. Here how many? Two moles are there. So that is 1 + 1 products minus two reactants. That is 2 - 2 that becomes zero. When delta n is zero, the relation between delta h is equals to delta e plus delta n rt. So delta n is zero means therefore in this condition delta h is equals to delta e.

[01:13:16]In this condition delta H is equals to delta E. Right? So this is the one example we'll get the relation right. So next one more reaction I will give Hber process many times it will be utilized right the synthesis of ammonia in habber process. Right? So that is N2 is combined with H2. So that can be produces NH3 that can be produces NH3.

[01:13:42]So these all are gases gas gas and this is the gas molecule right or else not only equilibrium condition we may take directly reaction right so all our gases right how many moles of this we have to take three moles of hydrogen and 2 moles of ammonia we'll get so therefore here we have to calculate delta ng delta ng means what are the number of products number of moles of products will be two number of moles of reactants will be three and here will 1. Therefore 2 - 3 + 1 that is 2 - 4 that is -2. Delta ng is -2. Therefore what is the relation?

[01:14:22]Delta h is equals to delta e plus delta ng rt delta ng rt right delta ng is minus2 means delta h is equals to delta e minus 2 rt right? Delta E minus 2 RT some value we are removing from this right so means hence delta H is less than of delta E this is the relation we'll get here in this case delta H is equals to delta E but here delta H is less than of delta E so how we are getting this delta H and delta E with the help of bomb calorometer and water calorometer from that how we are getting the questions based on that that will be discussed Right.

[01:15:26]Right. So this is the topic today's topic. Right. So we'll continue this one in the next class.