Under what conditions might a reaction be endothermic but exergonic? Explain.

Question

Accepted Answer

Welcome back, everyone. Based on the Gibbs free energy equation, delta G gives free energy change is equal to delta H minus T delta S. Which of the following correctly explains when a reaction might be endothermic. But ex ergo we have choices A through D which explore different scenarios concerning the way an endothermic reaction can become ex ergodic through either an increase in entropy or decrease in entropy and the balance with entropy changes. And as a whole, the collective impact on it gives free energy. So based on our textbooks, we're going to recall that for an endothermic, I'm sorry for an endothermic reaction that would correlate to an entropy chains change which is positive. So a positive delta H and for an ex Orgo reaction that would correlate to a negative gibbs free energy change. Negative delta G recall that in an E exon reaction energy is released. Whereas in an endothermic reaction, we would observe an absorption of energy by the reaction from its surroundings, which is why it makes sense that entropy change should be positive for an endothermic reaction. Because the prompt tells us that the reaction should be both ender endothermic and exotic. We're going to then recall our Gibbs free energy change formula in which Gibbs free energy change, delta G is equal to entropy change, delta H minus the temperature of the system multiplied by delta S, the change in entropy or disorder. And so plugging in the corresponding signs based on what the prompt outlines, we should have a negative sign substituted for delta G which is set equal to the positive sign substituted for delta H for the endothermic reaction. And that is subtracted from T times delta S. And we're going to recognize that temperature must be positive. And so therefore, only entropy changed delta S. It can be manipulated in order to make the reaction both endothermic and organic. And so therefore, that means the entropy change delta S should be large and positive enough of a value in order to offset the difference from the temperature, sorry to offset the difference from the entropy change, which is positive so that we can result in a negative value for gives free energy change, delta G for the reaction. And the only way that entropy would be large enough in order to ensure a negative delta G or gives free energy change is when there is a sufficient and large increase in entropy or disorder. So going to our answer choices, choice a states that an endothermic reaction becomes exer agonic only when the endothermic reaction involves an entropy increase large enough to cause the negative T delta S term in the gives free energy equation to outweigh the positive entropy change term resulting in a negative gives free energy change. And so far choice A certainly aligns with the notes we outlined below. Moving on to choice B. It states that an endothermic reaction becomes ex ergodic only when the endothermic process involves an entropy decrease large enough. And just off of the strength that it says a entropy decrease, we would automatically rule out choice B since as we stated, we need entropy to be an increase that is large enough to cause the negative T delta S term in the Gibbs free energy equation to outweigh the positive entropy change term. So moving on to choice C, it states that an endothermic reaction becomes ex ergodic when the endothermic reaction involves an entropy increase small enough and so small enough would also be the reason why we can rule out choice C. We wouldn't even continue considering it. And then we've got choice D which states that an endothermic reaction cannot be an ex ergodic reaction because entropy change is positive, which by default results in a positive delta G and that would be untrue. That's a false statement because we would need to have a negative, gives free energy change. And so we would rule out choice D and that means that choice A is the only correct explanation for why a reaction can be endothermic. But ex Ergodic, so A is our final answer, which states that again, an endothermic reaction becomes exer agonic only when the endothermic reaction involves an entropy increase large enough to cause the negative T delta S term in the delta G equation or gibbs free energy change equation to outweigh the positive entropy change term resulting in a negative gibbs free energy change. Delta G. I hope this made sense and let us know if you have any questions.

Under what conditions might a reaction be endothermic but exergonic? Explain.

Verified video answer for a similar problem:

Key Concepts

Endothermic Reactions

Exergonic Reactions

Gibbs Free Energy