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Problem 65

The scenes and the graph relate to the reaction o…


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Problem 64

How is the free energy change of a process related to the work that can be obtained from the process? Is this quantity of work obtainable in practice? Explain

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Video Transcript

We want to explain the relationship between the Change and Gibbs Free Energy or Delta G of a given process and the maximum amount of useful work that is generated from that process. The general equation that is used to describe this relationship is that the changing Gibbs free energy of a system Delta G system is equal to the maximum amount of useful work it can be attained from that process. This relationship holds a constant values or the temperature in the pressure of the process. Furthermore, there is a difference between spontaneous and non spontaneous reactions in terms of how that work is delivered or spontaneous processes. We know that these occur naturally with no input of energy. So if it's a chemical reaction, for example, than work is being generated by the system. And so Delta G is equal to a negative value for that maximum attainable work of the system. Because for spontaneous reactions, the system is doing work on the surroundings and therefore work is leaving the system in the form of energy. So that's why that would come out to a negative out You. Conversely, for non spontaneous reactions, we know that these do not occur naturally and therefore require some input of energy in order to be able to drive that process. So in that case, the Delta G is equal to the amount of work that the surroundings must do on the system in order to drive that process. So energy in the form of work is being supplied to the system. And so we have this positive value. But in either case, Delta G for spontaneous processes since the system is doing work on the surroundings, this is the maximum amount of work that can be generated by by the process, whereas for or non spontaneous processes with a positive value of work, meaning the surroundings have to do work on the system in order to drive it. That corresponds to the minimum amount of work that must be done on the system by the surroundings. So that's the general relationship between between Delta Delta G of a system in the maximum attainable work. We also want to determine whether or not in practice, all of this available work in each case is is used in real life. An answer to that problem that part of this problem is no because The reason for that is that energy leaves a system in a lot of a lot of different forms, but mostly mostly in the form of heat. For example, if we have an exo, thermic reaction, we have heat energy leaving the system. We have a system that that we're powering that has moving parts. Then then that energy could also be dissipated through shaft work. And so, in practice, we can never use up all of this available work from a system because that only works for reversible processes. In real life, the amount of Delta G for a given process relates to in an irreversible process. And for that reason, we're always losing energy, usually in the form of heat, from exo thermic reactions with a negative value of Delta H. And so that is why we cannot always use that maximum amount of work generated by a Delta G

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