Quick Revision 1 Thermodynamics

Ajouté : 2026-05-09

[00:00:00]Hi Andy already we completed thermodynamics chapter. So now we will see thermodynamics quick revision and uh which is useful for more number of revisions and uh I will explain based on PCB syllabus what are the concepts mentioned in PCB syllabus uh in which I will give you important concepts into important equations. Okay. So by which you can do more number of revisions and right. So we know that even from basic concepts also previously questions given last time PCB if you see seven questions given from thermodynamics very basic questions given from thermodynamics quick.

[00:00:50]So thermodynamics deals with what? Heat changes during various physical and chemical processes. Right? What is the amount of heat absorbed? What is the amount of heat evolved during various physical and chemical process that we'll study under thermodynamics? If heat is absorbed, if heat is absorbed that is called what? Endothermic process.

[00:01:19]If heat is evolved that is said to be what? Exothermic process.

[00:01:27]Okay. And one of the important applications of thermodynamics is it gives information about feasibility whether a given process can occur or cannot occur under a given set of conditions. We are mixing A and B at a given temperature and pressure. Whether such process can occur or cannot occur.

[00:01:44]If you drop some water here, whether it flows from upills to downhills spontaneously or not, why it flows spontaneously, what is the driving force for that flow of water from upills to downhills? Those things we can study under thermodynamics. But limitations are it cannot give information about speed of process. It gives whether such process is feasible or not. But what is the speed of process that we can get from chemical chinetics? mechanism of process that we can get from chemical kinetics.

[00:02:16]Next, it is applicable to macroscopic systems only. It is applicable to macroscopic systems only. System consisting of large number of particles.

[00:02:27]Okay. It is not applicable to microscopic particles. That means each individual particle, atom or molecule that we study under atomic structure or quantum chemistry. This question was given and last time PCB thermodynamics is applicable to direct question given and thermodynamics is applicable to which systems and macroscopic systems it is not applicable to each individual molecule are at a microscopic systems and okay uh next thermodynamics gives what condition for equilibrium when a reaction comes to equilibrium. What is the condition for equilibrium? Next one, efficiency of heat engines and neiat energy is converted to work energy. We are giving 100 JW of heat energy. We are getting 70 JW of work energy. That means efficiency is 70%age. So we can calculate efficiency of heat engines.

[00:03:32]Right?

[00:03:35]So right this is small introduction to thermodynamics and right next one to get some idea on thermodynamics you have to possess some idea on various terms used in thermodynamics and to get kon thermodynamics you have to possess idea on these terms and that is system and surroundings. What is systemic? It is the part of universe which is under our observation on which part we are focusing and that part is said to be system only. What is surroundings? All the remaining part other than system. Okay. Remaining part of the universe. So except system all the remaining part is said to be what?

[00:04:19]Surroundings to that system. remaining part that means this you may remember and system plus surroundings is nothing but what universe system plus surroundings is nothing but universal how many types of systems we have three types of systems we have three types of systems open system in the case of open system both heat is exchanged between system and surroundings matter is also exchanged between system surroundings. For example, boiling of water in open vessel. If you take boiling of water in open vessel, both heat is exchanged and matter is also exchanged between system and surroundings. If you take closed system, so closed vessel boiling of water in closed vessel whether water escapes into surroundings or doesn't escape into surroundings and it doesn't escape into surroundings. That means only heat is exchanged and no matter exchange.

[00:05:19]And next one isolated system.

[00:05:23]If both are not exchanged and neither heat nor matter exchange between system and surroundings that is called isolated system. Ideal thermos flask. Ideal thermos flask we may take as isolated system and right this is the classification of systems. Right. Next one.

[00:05:49]Next if you see extensive and intensive properties and extensive important and extensive and intensive properties. If a property depends on amount of the substance or number of moles of substance that is said to be extensive property. examples if you see length, mass, area, volume, force. Okay, force also depends on what amount of the substance.

[00:06:21]Next, the various thermodynamic properties like uh internal energy, enthalpy, gives free energy, heat capacity, okay, entropy, all these depends on what amount of the substance.

[00:06:35]So all these are said to be what?

[00:06:37]Extensive properties. Next what about intensive properties whether depends on amount or they do not depend on amount. They do not depend on the amount of the substance. Example if you see pressure concentration density okay pressure force per unit area concentration number of moles per unit volume density mass per unit volume if you express a property per mole per g per unit area per unit volume that is said to be what intensive property okay for example molar uh internal energy we are expressing for one mole heat capacity is extend property but molar heat capacity specific heat capacity means for 1 g specific heat capacity intensive doesn't depend on amount of the substance color temperature okay temperature doesn't depend on the amount of the substance various properties of solvent like refractive index like refractive index surface tension viscosity surface tension viscosity.

[00:07:55]Okay. All these whether depends on the amount of the substance or doesn't depend on the amount of the substance.

[00:08:00]They do not depends on the amount of the substance. It depends on nature of solvent not on amount of solvent. Okay.

[00:08:07]Next one. PH. PH is equal to minus log concentration of pH depends on indirectly concentration only concentration is intensive. Electrode potential. Electrode potential also depends on concentration only but concentration is what? Intensive property. So like this these are the various examples we have for intensive properties and chemical potential. What is chemical potential and chemical potential is nothing but gives free energy per one mole and gives free energy per one mole. Molar gives free energy. Molar gives free energy is also called as chemical potential. Since we are expressing for one mole, it is said to be intensive property. Okay? You remember the examples only. Okay? And the ratio of two extensive properties is what? Intensive property. The ratio of two extensive properties is intensive property. For example, density is equal to what? Mass by volume. Mass is extensive property. Volume is extensive property. Mass by volume is what?

[00:09:09]Intensive property. Okay.

[00:09:13]Next extensive properties are said to be added to that means if you know extensive property for one gram you can you may calculate for any number of grams. If you know for one mole you can calculate for any number of moles. So extensive properties are said to be what? Additive. Okay.

[00:09:32]Right. Uh this is about extensive property and intensive property. Next one path function and state functioning.

[00:09:39]The name itself indicates the change in property depends on path followed. For example, we are doing a process A to B by two paths. And this is path one and this is path two. Initial and final states are same in both the cases.

[00:09:56]Initial and final states are same in both the cases. Path is different. For example, if you measure a property, if you are getting different value, then the property X depends on what the path followed depends on initial and final states. Then X is called what?

[00:10:14]Path function.

[00:10:17]If you are getting same value by two paths and okay for example Y delta Y1 is equal to delta Y2. So Y for property Y we are getting same value by two paths.

[00:10:29]That means y is set to be what? State function. Y depends only on initial and final states. It depends only on states not on path only. Okay. Examples for path function if you see as long as we are studying thermodynamics mainly two examples we have for path functions and work and heat and work and heat or heat capacity.

[00:10:53]Okay. All the remaining are all the remaining are state functions and so what are the examples for state functions if you see what are other than work and heat and mainly temperature internal energy enthalpy kips free energy entropy all these are state functions okay they depends only on initial and final states not on path followed Even W + Q according to first law W + Q is equal to what? Delta U and according to first law W + Q is nothing but delta U. So internal state function. So W plus Q is also um W plus Q is also state function.

[00:11:42]Next QP amount of heat exchange at constant pressure is delta H. Amount of heat exchange at constant volume is deltaU. So those two are also heat of reaction. Heat of reaction at constant volume and constant pressure also state functions. Heat is part function but heat of reaction is state function. Heat of reaction at constant pressure is delta h. Heat of h at constant volume is delta u. Both are state functions only.

[00:12:15]Okay. Uh that is the concept of state functions and right the change in state function for cyclic process and here x is state function that is equal to zero and cyclic process means initial and final state are same state function depends on initial and final state. So the change in state function for cyclic process is zero. For example integral du dh all are equal to zero. But integral dq or dw are not equal to zero. They are path functions. So they are not equal to zero.

[00:12:55]Okay. This is the concept of state and path functions and next one internal energy. Internal energy is nothing but sum of the various forms of energy present in the system. Simply it is the sum of the potential energy and kinetic energy. But absolute value of U is not possible to determine. Only change in internal energy we can determine experimentally.

[00:13:17]Okay.

[00:13:19]So deltaU is nothing but what amount of heat exchanged during a process at constant volume. Constant volume means closed vessel we have to take and we have to take cylinder with fixed piston and no immovable piston we have to take.

[00:13:35]Immovable piston means constant volume.

[00:13:38]Okay. Delta U. Amount of heat exchange is equal delta U. For endothermic reaction it is positive. For exothermic reaction it is negative. Absolute values we cannot determine only changes we can determine.

[00:13:50]Next one enthalpy and enthaly mathematical expression for enthalpy is U + PV. And at constant pressure we can write as delta H is equal delta U + P delta V. As absolute value of U cannot be determined. Absolute value of H also cannot be determined. Only delta H can be determined. Amount of heat exchange at constant pressure is nothing but delta H. Again for endothermic reaction is positive. For exothermic reactity is negative 1. Small difference between U and H is U we follow at constant volume.

[00:14:24]H we follow at constant pressure. Delta U is also called as heat of reaction at constant volume. Delta H is also called as heat of reaction at constant pressure end. Okay.

[00:14:39]Next from next one work. What is the formula for work done? W is equal to what? We have minus P external pressure or opposing pressure into delta V and that is the formula for work done and D. Okay.

[00:14:57]While we are solving this generally units we may get liter atmosphere volume is in liters pressure is in atmosphere so we may get in liter atmosphere one liter atmosphere is equal to 24.2 2 calories and 1 calorie is 4.18 J. So nearly we will get 100 J exact value 1 something we have nearly we'll get one J 100 J one liter bar also we'll get same ide since one bar is nothing but what 987 atmosphere almost same both are same so one liter bar also we get nearly same 100 J only sometimes they're giving in the units of Pascal ending last time PCB they have given Pascal ending Pascal Means it is the unit for pressure force per unit area newton per m². Pascal means what? Newton per m².

[00:15:53]So kilo pascal liter or newton m is nothing but 1 j. kilopascal liter or 1 newton meter is jol and this is required and while we are doing unit conversion all these are mentioned you know in my basics material unit conversions values of various constants used all those are mentioned in my basic material once you refer my basics material right next if you are rising the temperature of a substance if you are rising the temperature of a substance what is the formula for work done is equal = to minus nr delta t and from ideal gas equation p delta v we can write as nr delta t if you're rising the temperature of 1 mole of a gas by 1°ree and so here 1 mole of gas 1 delta t1 so work done by the system work done during the process is minus r minus r means if it is in jles 8.314 jles in calories 2 r value is 2 minus 2 calories right we if you're rising the temperature of a substance So that is the formula we have to use.

[00:17:03]If you are doing a reaction only, if you are doing a reaction in closed vessel and in open vessel only in closed vessel, what is the formula for work done? W is equal to we have minus P external delta V. Closed vessel means no change in volume. No change in volume.

[00:17:21]So work done is zero. Work done is zero.

[00:17:24]Second one is open vessel or at constant atmospheric pressure.

[00:17:30]So we can calculate like this and minus p delta v we can write as minus delta n rt in open vessel means whatever the gases evolved those may participate in the reaction those may not reaction expansion whatever the gases evolved those may participate in the expansion.

[00:17:46]So work done is not equal to zero. Okay.

[00:17:49]So here gases may participate in the expansion. So that's why we have to consider only number of moles of gasous substance only delta n product side number of moles of gases substance minus reactant side number of moles of gases substance or during reaction how many moles of gases substance is evolved that we have to substitute any okay next one if internal pressure is more compared to external pressure and then what happens and work done by the system pushes piston Okay. On the surroundings.

[00:18:23]So work done by the system only. Work done by the system on the surroundings.

[00:18:30]Okay. Expansion. Internal pressure is greater than external pressure means expansion. Okay. Delta V positive and positive into negative is negative. Work done is negative and if work done by the system negative. If external pressure is greater than internal pressure and work done on the system we can we can say that work done on the system that is called compression only delta v negative formula is double is equal to minus p delta v delta v negative negative into negative positive. So work work done on the system is positive only work done by the system double is negative.

[00:19:11]Next, if internal pressure and external pressure both are same, then such situation is said to be mechanical equilibrium.

[00:19:19]Internal and external pressure are same that is said to be equilibrium.

[00:19:25]Next one, if you take free expansion, what is free expansion and expansion against vacuum? Free expansion.

[00:19:36]Expansion against vacuum and that is called free expansion. So vacuum means what about opposing pressure and is zero. External pressure is zero. So zero into something we will get zero. So no work done. That's why that is called free expansion.

[00:19:53]Okay. Expansion against vacuum is called free expansion.

[00:19:59]Next one heat and Okay. Both heat and work are forms of energy only. Heat.

[00:20:06]If temperature of system is greater than surroundings only then transfer of heat takes place from what system to surroundings. So heat is released by the system to surroundings. Heat is given by the system to the surroundings. In such case Q is indicated with negative sign.

[00:20:24]Since system is giving heat energy to the surroundings heat is given by the system to surroundings. Next if temperature of system is less than surroundings surroundings temperature is more always we know that heat flow takes place spontaneously from high temperature to low temperature. So flow of heat takes place from surroundings to system. System is absorbing heat energy.

[00:20:47]So Q we have to give it the positive sign.

[00:20:51]Q we have to give it positive sign. If system is absorbing heat energy this sign convention important. If temperature of system and surroundings both are same that is said to be what?

[00:21:01]Thermal equilibrium. That is said to be thermal equilibrium. Okay.

[00:21:12]Next and zero law of thermodynamics.

[00:21:17]According to zero of thermodynamics simple and if two systems A and B are in thermal equilibrium with the third system separately thermal equilibrium is for example it is at 25° centiggrade this is also at 25° centgrade this is also at 25° centgrade a and C are in thermal equilibrium B and also C also thermal equilibrium then indirectly all the systems are set to be under thermal equilibrium then indirectly all the systems are set to be all are at same temperature all are at same temperature. So all the systems are set to be under thermal equilibrium that is called zero law. Jerith law introduced a new concept that is temperature concept was introduced by zero thermodynamics. This is the question given under last PCB. Temperature concept was introduced by option zero first law second law like that options.

[00:22:12]Temperature concept was introduced by what?

[00:22:15]Thermodynamics.

[00:22:18]Next one.

[00:22:22]Change in heat internal energy occurs in the form of work or heat energy. If heat is absorbed by the system, positive.

[00:22:29]Just now we discussed if heat is evolved by the system negative. Work done by the system negative only. Double work done on the system double is positive only.

[00:22:38]Otherwise we can write delta U is equal to Q minus P delta V and so from this in the last time PCB one problem was given and last time PCB problem is given from this concept total seven questions given one is macroscopic system that that question was given next temperature introduced by zero law and based on this problem given Q Q pressure initial volume final volume the data is given they ask you to calculate change in internal energy and we have discussed many questions uh based on this ending.

[00:23:14]Okay.

[00:23:17]Right. Uh this is about first law of thermodynamics and right.

[00:23:27]Okay.

[00:23:30]Next if you see concept of heat capacity and C it is the amount of heat required to write the temperature of substance any amount of substance and by one degree and so Q by delta T and C is equal to Q by delta T.

[00:23:47]For example, if you take delta T is equal to 1 and 1°ree or 1 kel then the amount of heat required is called heat capacity. It is intensive property or extensive property. Extensive property depends on amount of substance. Okay. If you take more amount of substance, more heat we have to supply to raise its temperature by one degree. Okay. Let us consider this is per m g of substance.

[00:24:11]Next specific heat capacity means per 1 g and specific heat capacity. Yes, per 1 g and so to get per 1 g we have to divide with m and simply this is for m g of substance. For example, now I want to get for 1 g of substance and simply if you divide with m you'll get for m g of substance only. If m s and delta t is given how to calculate amount of heat required ms delta tn okay so after writing this short notes with important conclusions important equations you practice as many questions as possible and generally you will get grip in which situation we have to use which equation.

[00:24:53]Okay, in which situation we have to use which equation. So for that you have to practice as many questions as possible and then you will get griping. So if you follow the strategy easily you will cover 60 to 70%age of questions and okay short notes with important concepts and equations after that you have to practice as many questions as possible.

[00:25:15]So I am covering all these things today content okay good content and while I am explaining content I'm explaining where you have to focus whatever the questions given in various competitive exams all those things I am explaining after that I am giving various practice questions old questions also okay right specific heat capacity is intensive or extensive heat capacity is extensive property specific heat capacity is what intensive property since we expressing per gram intensive property that doesn't depend on the amount of substance.

[00:25:52]Next molar heat capacity at constant volume molar heat capacity at constant volume. So QV we have to substitute here QV means delta U by molar heat capacity means we have to get for one mole to get for one mole we have to divide with the total number of moles. If you divide with the total number of moles then we will get for one mole and delta t and so delta u is equal what? NC delta t and this is molar heat capacity at constant volume. Next what about mar heat capacity at constant pressure. QP we have to substitute QP means what? Delta H to get per one mole we have to divide with N to get per 1 g we divide with total mass to get per one one mole we have to divide with total number of moles and deltat T.

[00:26:42]So from this delta H is equal to what?

[00:26:46]NCP delta T whether these two are intensive properties or extensive properties any intensive properties.

[00:26:54]These two are intensive properties.

[00:26:56]Since we are expressing for one mole, they do not depend on the amount of the substance. They are said to be intensive properties.

[00:27:03]Next, if you take isothermal process, delta t0, that means delta U and delta HR zero. Very very important. And for an ideal gas, okay, if you want, I will share these pages also.

[00:27:20]For an ideal gas, U and H both are function of temperature only. For an ideal gas, U and H both are function of temperature only. So therefore deltaU u and delta h for an isoothermal process equal to zero and many times questions given based on this concept and repeatedly questions given and from this concept in various competitive exams and they are giving like this otherwise they are mentioning like this d u by dv at constant temperature d u by dp at constant temperature do h by dv at constant temperature do h by d at constant temperature that is equal to zero. Since here temperature we are maintaining constant and u and h doesn't depend on pressure and volume only. If pressure volume changes what happens the distance between the molecules may changes but in the case of ideal gases intermolecular forces are oppent. So even the distance between the molecules changes no change in the intermolecular forces. So no change in the internal energy and enthalpy. According to kinetic theory of gases kinetic energy is directly proportional to temperature.

[00:28:34]Okay. So u and h are function of temperature only.

[00:28:38]Okay. U is equal to what? Potential energy plus kinetic energy. Potential energy is related to intermolecular forces. Kinetic energy is related to motion. But intermolecular forces are zero. No intermolecular forces means potential energy zero only. So total energy is related to kinetic energy only. Kinetic energy is directly proportional to temperature according to kinetic theory of gases. So U depends only on temperature. Similarly H also function of temperature only.

[00:29:06]Right. Uh important this one.

[00:29:10]Next, what is the relation between CP and CBD? CP minus CV is equal to NR for N moles and while you are using this formula here. CP you have to substitute for N moles C. CV also we have to substitute for N moles and if you apply this equation for one mole we get like this. CPM minus CVM is equal to number of moles N. If you substitute RN CP minus CV is equal to RNA.

[00:29:37]Okay, this is at constant pressure. This is at constant volume. This is open vessel. This is closed vessel. Okay.

[00:29:46]In closed vessel, if you are rising the temperature of a substance for example, we are doing boiling of water in closed vessel. We are supplying heat energy. Is there any work done or no work done? No work done. Only internal energy increases. But here work will be done and internal energy also changes only.

[00:30:04]So these two gets cancelled. So gas constant can be defined as according to this equation gas constant can be defined as work done by one mole of an ideal gas at constant pressure and how can we define gas constant and work done by one mole of an ideal gas at constant pressure and R value is positive and so that means CP is greater than CV.

[00:30:27]Since here work done is zero only. Okay.

[00:30:31]Whatever the heat energy we are supplying that is utilized to increase the temperature only. But here whatever the heat energy we are supplying is utilized in two ways. To increase the temperature another one is to perform work done. That's why more amount of heat is required. Okay. You are raising the temperature of water in closed vessel and open vessel where more amount of heat is required. In open vessel more amount of heat is required. So that is CP is greater than CV ending. Okay. H and next one atomicity of a given gas we can guess based on gamma value. Gamma is called heat capacity ratio or adiabatic index and gamma is nothing but CP by CV or SP by SV and this is called as heat capacity ratio or adiabatic index.

[00:31:26]This is called as heat capacity ratio or adiabatic index.

[00:31:33]Okay.

[00:31:42]If you take for monatomic for monatomic CV value 3x2 R three translational motions contribute and only three translational motion no rotational motions. So CP is equal to what? CV + R 3x2 R + R that is 5 by2 RNA. So gamma CP by CV 5 by3 we will get 1.66 based on this also previously questions given this question was given in TGO chemistry last time TGO chemistry if gamma value 1.66 that is said to be what monatomic gas 1.66 Six is that is called monatomic gas or diatomic gas and CV three translational motions two rotational motions and so 5 by2 R CP is if you add R we will get 7 by2 R so gamma 7x4 1.40 if gamma value is 1.40 that is diatomic acid poly or triatomic acid tri polyatomic gas C three translational motions three rotational motions and 6 into each motion contributes 1x2 R and 3 R CP means 3 R + R 4 R so gamma is 4x3 and that means 1.33 gamma value is 1.33 such gases to be tri polyatomic gas in Okay, next one. CP minus CV is equal to we have R. What is the expression for CP and CV with respect to gamma? This question also given last time PCB and right. If you divide on both sides with CV, cp by CV is nothing but gamma minus one is equal to R by CV. So what is the formula for CV and R by gamma minus one?

[00:33:32]This is for one mole and if you want for n moles nr by gamma minus one this question was given in last time PCB.

[00:33:42]Okay. So while I am explaining short notes itself I will cover seven questions given to you from thermodynamics and uh so far I think four questions covered in microscopic system.

[00:34:00]Okay. Microscopic system.

[00:34:03]Next delta U is equal Q minus P delta V.

[00:34:05]From the problem given in temperature zero law introduced a new concept that is temperature and past law introduced a new concept what energy and first law introduced a new concept. You remember energy and this is the question given. Now what is the formula for CP and CP by CV is equal to gamma. So from that CP is equal to gamma into CV and that means gamma R by gamma minus one that is the formula for CP and with respect to adiabatic index with respect to adiabatic index.

[00:34:43]One more question given in last time PCB if you see specific heat capacity what is the formula we have for specific heat capacity Q by M into delta T q by M into delta T. The same question given previously in JL also and what about specific heat capacity for isoothermal process for isoothermal process. What about specific heat capacity? Isothermal process means delta t ts to zero something by zero is what? Infinity. So s ts to infinity. But answer wrong.

[00:35:17]Okay. Infinity. But for isothermal process delta ts to zero. So entropy tends to entropy and specific heat sorry specific heat tends to infinity and this is the question given last PCB right these are the heat capacity concepts and Next one, calculation of work done by graphical method and pressure versus volume graph may be given to you.

[00:36:01]Pressure versus volume graph may be given to you. They may ask you to calculate work done. For example, like this given process. So the work done is nothing but the area below that line end. Work done during the okay system is changing from V_sub1 to V2. Work done is nothing but area below that line and area of rectangle. Area of rectangle is nothing but what? Length into breadth and L into B. We have to calculate it. Okay. For example, cyclic process is given. Pressure versus volume. Cyclic process right angle triangle is given. This is a cyclic process.

[00:36:36]How to calculate work done? Work done is nothing but enclosed area per cyclic process. That means double is equal to what? Half into base into height of BH half into base into height. Okay. Based on that we have to calculate any for example like this given pressure versus volume again cyclic process A B C D E A I'm giving clockwise cyclic process clockwise cyclic process if you see network done by the system only network we will get negative only mostly they are giving magnitude only but positive value negative value also given we have to choose negative option negative value. So nothing but what enclosed area again area of rectangular that is L into B. If it is given anticlockwise cyclic process only we'll get network done on the system and that means W is equal to positive. Okay, like this we can calculate graphically work done during a process and this is one of the methods we have to calculate work done graphically and okay so next one calorimetry mentioned in our syllabus calorimetry is the technique by which we can determine heat changes and okay during various physical and chemical process to determine heat changes during various physical and chemical process we Follow calorimetry technically in that bomb calorimeter is mentioned in your syllabus study. Bomb calorimeter.

[00:38:15]Bomb calorometer. By using bomb calorimeter we can calculate change in internal energy. By using bomb calorimeter we can determine what change in internal energy. Bomb is nothing but sealed vessel. Okay. In which we must take sample whose delta U we want to calculate. Let us consider small M gs of sample. We may take it under go combustion. Combustion is exothermic process. Okay. Heat is evolved by you whatever the heat evolved that rises the temperature of water or calometer components present in the this system only. Okay. So we have thermometer to note the rise in temperature and based on the rise in temperature we can calculate delta. If more amount of heat is evolved more rise in the temperature that means more change in internal energy. Here we are doing combustion.

[00:39:03]Combustion is an exothermic process. So we get ne we have to give with negative sign and so delta U for one mole of substance only. DeltaU per one mole of substance is given as formula minus capital M by small M into C delta T and D. This is the formula we have negative sign we are getting since combustion is an exothermic process. Capital M. Small M is the mass of sample we are taking in the calorie meter and C is heat capacity. Delta T is rise in temperature that we note by using thermometer. Okay.

[00:39:39]Already.

[00:39:42]Okay. Right.

[00:39:45]And once if you know delta U, how to calculate delta H for a reaction? This is also important in many competitive exams. Question given based on this delta H is equal to delta U plus RT delta N actual formula is P delta V.

[00:40:04]If you take reactions involving solids or liquids delta H is almost equal to deltaU since change in volume is negligible for the reactions involving solids and liquids. So delta H and delta U almost the same. But for the reactions involving gases delta H is equal delta U plus RT delta N where delta N is product side gaseous substance minus moles of gas substance reactant side moles of gas substance important and this RT we will get repeated. What is the value of RT in kiloj?

[00:40:43]What is the value of RT in kilogjans?

[00:40:46]Repeatedly we will get at this one. If temperature is given 25° centigrade or 27° centigrade or 298 kel or 300 kel around this value is given temperature and R2 value in kilogj is 2.5 kiloj.

[00:41:06]Okay. RT value here it is 2.5. Last time in AP forensic in GATE exam, CSR various competitive exams question given based on this right like this we can calculate delta H once if you know delta UI they're asking like this what is the difference between heat of reaction at constant pressure and heat of reaction at constant volume that means delta H minus delta U1 which is nothing but what RT delta N right after this we have to discuss various thermodynamic processes and the various thermodynamic process, various thermodynamic processes, isothermal process which remains constant temperature no change in the temperature but heat is exchanged between system and surrounding. If you take isoothermal expansion and whatever the heat required okay that is taken from surrounding side. So Q is positive and the energy required is taken from surrounding. If you take isoothermal compression whatever the heat evolved that is given to surrounding. Whatever the heat evolved that is given to surrounding. So Q is negative 1 or from first law we know delta U is equal to Q + W. Delta U is zero. So Q is equal to minus W or okay Q is equal to minus W or this is zero and R or minus Q is equal to plus W.

[00:42:56]Work done by the system is equal to heat absorbed and positive work done on the system. Compression means on the system.

[00:43:03]Work done on the system is equal to heat given to the surrounding negative. And for isothermal process, ideal gases follow boil law. According to boil's law, pressure is inversely proportional to volume or P1 by P2 is equal to V_sub_2 by V_sub_1. Right? Generally isothermal process are carried out in constant temperature bath that is the end.

[00:43:27]Okay. Next one. Isoothermal free expansion as well as adiabatic free expansion. For isothermal free expansion and adiabatic free expansion all are equal to zero. Delta U is equal delta H is equal to W = Q is equal to zero. All are equal to Z for isothermal as well as adiabatic free expansion.

[00:43:51]Next one ediabotic process. Ediabotic process amount of heat exchanger is zero only between system and the surroundings but deltat t is not equal to zero. If you take adiabatic expansion only if you take adabatic expansion whatever the energy required for expansion taken from internal energy since no exchange of heat between system and the energy required is taken from its internal energy internal energy decreases. So temperature also decreases.

[00:44:22]So gas is cooled and adiabatic compression if you take okay energy released whatever the energy released not given to surroundings remains in the system only the energy released remains in the system only so system internal energy increases so temperature also increases generally these are carried out in insulated vessels process are carried out in insulated vessels no exchange of heat between system and surroundings things.

[00:44:53]Next one.

[00:44:56]What is the relation between pressure and volume for adiabatic process and okay PV power gamma is equal to constant. Gamma is nothing but heat capacity ratio.

[00:45:07]Temperature and volume TV power gamma minus one is equal to constant.

[00:45:14]Temperature and pressure mainly these two important temperature pressure somewhat complex problems PV power gamma is equal constant TV power gamma minus 1 is equal constant these are the relations between pressure volume temperature for an adiabatic processing if you apply law to adabatic processing we have deltaU is equal to Q plus But amount of heat exchange is zero. So delta U is equal to W. Or we can write minus deltaU is equal to minus W.

[00:45:52]Okay. Plus W means work done on the system. Work done on the system means compression is equal to plus delta U means increase in internal energy.

[00:46:02]Minus W means work done by the system.

[00:46:04]Work done by the system is equal to what? Decrease in internal energy. Okay.

[00:46:08]Work done on the system. Compression increase in internal energy. Work done by the system is equal to what? Decrease in internal energy. This is adiabatic processing.

[00:46:22]Next one isobaric process which remains constant and the pressure remains constant.

[00:46:29]Pressure remains constant. Generally these are carried out at constant atmospheric pressure or cylinder with movable piston. Cylinder with movable piston at constant pressure amount of heat exchange is nothing but what? Delta H. We know that from ideal gas equation PV is equal to NRT. P is constant. So volume is directly proportional to T for isobaric process. I think it is charless law. Okay. At constant pressure ideal gas is follows charless land.

[00:47:01]Next isoric process which remains constant volume. DV or delta V is equal to zero. Amount of heat exchange at constant volume is equal to what? Change in internal energy. Generally this process are carried out in closed vessels with immovable piston cylinders with immovable piston. Work done is what? Zero during isocoric process and from ideal gas equation PV is equal to we have NRT volume constant. So P is directly proportional to temperature. I think idle gases follow what yellows law at constant pressure. Yellow law at constant pressure cyclic process and initial and final state is same. That is called what?

[00:47:52]Cyclic process.

[00:47:58]Your initial state and final state are same. That's why change in state function delta x that is zero per cyclic process cyclic process okay change in state function x is state function delta u delta h delta s all those are equal to zero otherwise we indicate like this also cyclic process change in state function for cyclic process is zero. So these are the various uh thermodynamic processes we have only right okay uh remaining I will explain in one more session right almost 50% of the concepts we completed and okay so like this you have to prepare short notes and for each topic like this uh we don't know whether we may get time or not just for sample how you have to prepare short notes okay that I am explaining here and this is the way by which you can prepare short notes and right I will continue in the next session and remaining short notes thank This