 We will not use that method, that method is longer, we will do the other method, for an easy one less time. Now what is the energy, what is the energy, what next? What is the physical significance of which energy? Spontaneous. Spontaneous? Spontaneous. It is a non-expansion work, non-useful work, non-feeling work. What do you mean by non-useful work? Spontaneous. Yes. A derivative of the useful work, and we also call it as a non-expansion work, and which is nothing but non-TV work. The useful work means what, suppose I will take one chair from here and put it over there, right? There is no expansion in this case, but I have done some work, right? So worker in this case will be equal to work, but decreasing my history energy, that is useful work, non-expansion work. Even the pressure volume curve is not involved, right? So anyway, you do some work, you do that work on the cost of your history energy, right? So this is delta G useful work, non-expansion work and non-TV work, right? So delta G, in case of a cell, it is defined as the charge into potential, Q into V, right? In case of a cell, delta G is defined as the negative of the charge into potential V. If Q charge moves under a potential difference V, then the work done is what? Since the delta G is decreasing to like to minimize or to neglect that the negative curve, we have used this negative sign. It is decreasing, delta G will be negative if you do not put negative sign over there. Work done negative does not mean anything, right? That is why we use the negative sign over there. Q into V is the decrease in Gibbs free energy in case of an electrochemical cell, correct? Now, thing is what? You have to just find out what is this Q and what is this V? That is it, that must be question is that, okay? Q is what? Q is the charge and what is the charge we are using here? N mode of electron, right? The charge here is what? Q into mind now, what is the charge on N mode of electron? N into 1.6 into 6.02 into 10 to the power 23, right? So, this is what? For 1 mole of electron, see the 1 mole of electron the charge is what? 6.02 into 10 to the power 23 for 1 mole and the charge on 1 electron is 1.6 into 10 to the power minus 90. This is the charge on 1 mole of electron, right? Charge is important when we do the electro, light cell there also we have used this, okay? Charge on 1 mole of electron is this and when you solve this approximately in ways, 965 equals 0 to lump, which is nothing but 1 paradigm, right? So, charge on 1 mole of electron is 1 paradigm, charge on N mole of electron is N paradigm, right? Because we have N mole of electron, so Q is equals to what we can write? N paradigm is N into F, yes? Yes. Okay, now what is V? V is the potential difference, correct? But in case of the cell, what is the potential difference in the EMF of the cell? Potential difference is nothing but the EMF of the cell, because of that only the charge is going, right? So, V is nothing but the EMF of the cell. So, when we substitute these two from here, delta G becomes minus N M E. This is the formula of delta G in an electron free cell, understood, right? Now, we know this formula and we have done this in thermodynamics. The delta G is equals to delta G naught minus 2.303 RT log Q. What is Q? Q is reaction constant, everything you forgot. Kc is equilibrium constant, but Q says Q only. Kc is equilibrium constant, that is defined at equilibrium. But at any other point, the ratio of product by reaction is what? Reaction constant Q, right? So, when we apply the condition of equilibrium, right? We have a specific case, because Q is nothing but the concentration of product by concentration of reaction, right? Since we are not taking the case of what? Equipment, right? So, at equilibrium Q is equals to case. Now, when we substitute this, delta G is equals to minus N M E cell. So, delta G naught is what? Minus N M, T naught is basically the standard state. Now, these are coming to be substituted here. It becomes minus N F E cell is equals to minus N F E naught cell minus 2.303 RT log Q. E cell is equals to E naught cell plus 2.303 RT log N F log of Q. I think it is plus, we have here, delta G naught plus 2.303 RT log. That is why when equilibrium is there, delta G will be 0, Q is equals to Kc and delta G naught becomes minus 2.303 RT log Kc. We have a plus sign of it, right? So, when you divide by minus N F, it becomes minus sign of it, right? So, E cell is equals to E naught cell minus 0.0591 by N log of, or we can write it as concentration of product by concentration of reactant. This equation is non-sequential. When we substitute this R value, T is 298 Kelvin and F is 965, that was 0. When you substitute all this value except this N, because N is what? N is the number of moles of electron that is exchanged, right? So, according to the reaction N will vary. So, I will take this N as it is, when you substitute all this value, you will get 0.0591, okay? So, this equation of this equation is known as non-sequential equation. Electrochemical equation is non-sequential. All other things I have to discuss only with getting on that question, okay? The numerical problem is to get one more. One more important point to write down, this delta G is an extensive property. Extensive property and extensive property are additive. Intensive property are non-arrative, like EMI of this. 1,000 questions. Write down, calculate E naught for the reaction. Calculate E naught for the reaction, Fe3 plus plus electron gives Fe2 plus. For this reaction, you have to find out E naught. The data given is E naught for Fe3 plus to Fe is minus 0.03620. And the data is E naught of Fe2 plus to Fe is minus 0.440. You have to find out E naught for this reaction. The first equation is applied to both half cell reactions and for non-sequential. Apply to both half cell reactions. Oh my God! 0.4 through 3, right? Yeah, 0.4 through 3. 0.4 through 3, right? Yeah. Okay. Okay, you see from these two data, you have to obtain this. So from this data what we can write, it means the reaction is for Fe3 plus plus 3 electron gives Fe3, right? And suppose this is E1 and E naught 1 is minus 0.03620. And then what we are doing is Fe2 plus plus 2 electron gives what? Fe and suppose this E naught 2 is minus 0.4401. How do we get the first reaction from this reaction? Fe2 plus on the product side, right? So we will just reverse this reaction and add these two, right? So when you reverse this, E2 becomes positive, right? So when you reverse this reaction, the reaction becomes Fe gives Fe2 plus 2 electron. So E naught 2 becomes 0.4404. When we add these two, what happens then? Fe3 plus plus 1 electron gives Fe2 plus, right? This is what the reaction we have, okay? So for this, the E naught of this reaction will be equals to E1 naught plus E2 naught. And that will be minus 0.0362 plus 0.44. When you solve this, what is the answer you get? 0.40384. Understood? Yeah. But this is wrong. Yes, you cannot do this. Why? That's so much over here. It's not related. It's not related. EMF of the cell is what? Non-addict first class only. EMF is an intensive property. It cannot add directly or subtract. So what do you have to do here? This is correct. Till here it is correct, right? Till here it is correct. But this we cannot do. E, we cannot add directly. But delta G is an extensive property. Delta G we can add, right? So we have to find out the delta G for this reaction. Delta G1 is equals to what we can write? Minus NF E1 naught, right? For this delta G2 is equals to what? Minus NF E2 naught. Since we are adding these two, so for this reaction, if it is delta G3, then delta G3 is equals to what we can write? Delta G1 naught plus delta G2. We can add delta G directly or subtract. Understood? Yes? Now what is delta G? Minus NF E1 naught minus NF N1, this would write actually. NF N1 and N2. Minus NF N1 naught plus NF N2 F minus N2 F E2 naught. And delta G3 is what? Minus N3 F E3 naught. Okay, F gets cancelled. E3 naught we have to find out. E3 naught is equals to what? This minus gets cancelled, this minus gets cancelled. E3 naught is equals to what? N1 even naught plus N2 E2 naught by N2. Now you see, since N1 N2 and N3 is not equal, here N1 value is what? 3. N2 value is what? 2. And N3 value is what? 1. If this is equal to N1 N2 and N3, then this will get cancelled. Then the expression will be what? E3 is equals to even plus E1. So this E3 is equals to even plus E2 if you can write, when all the electron exchange and all these reactions are equal. Otherwise you cannot write. That is one special case when the electrons exchange are equal. But since it is not heritally what we cannot add EMF of the cell or subtract directly. But what we do, we find out delta G. Delta G we can add or subtract according to the reaction. We substitute delta G in terms of E of the cell and then we find out EMF of the cell. N1 value is what? 3, right? 3 into all the value you have to substitute minus 0.0362 plus N2 value is 282. 0.440. Remember this reaction I have reversed. Okay? E3 will be positively but negatively. This divided by what? N the value is? Solve this negative answer. Then what is answer negative? Answer? 0.772. 0.772. Clear 0.772. 0.772. The answer is 0.772. What is the answer? 0.53. 0.53. Shikha is getting 0.53. Is it 0.153? 0.153. 0.153 is the answer. 0.153. Minus 0.153 is the answer. 0.153.