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Ch.18 - Thermodynamics: Entropy, Free Energy & Equilibrium

Chapter 18, Problem 125

Is it possible for a reaction to be nonspontaneous yet exo-thermic? Explain.

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Hey everyone were asked, can an XR thermic reaction be non spontaneous, justify your answer. To answer this question. We need to recall our standard gibbs free energy equation which is delta G. Is equal to delta H. Which is our change in entropy minus our temperature times our delta S, which is our change in entropy. So we were told that we have a non spontaneous reaction which means that our delta G must be Greater than zero. So it would have to be positive. And we were also told that we have an exhaust thermic reaction, which means that our delta H must be negative Now in order to get our delta G to be positive. This means that our delta S must be negative or in other words must be more ordered. And this must occur at low temperatures because we want to make our temperature times our change in entropy less than our change in entropy. So to answer this question, our answer would be yes. When the reaction has a negative delta S. Which means more ordered. And at low temperatures the term temperature times DELTA S. Will be more negative than DELTA H. Making the reaction non spontaneous. So I hope this made sense. And let us know if you have any questions
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