Two curves are shown in the following energy diagram:
b. Which curve represents the spontaneous reaction, and which the nonspontaneous?

Question

Two curves are shown in the following energy diagram:

b. Which curve represents the spontaneous reaction, and which the nonspontaneous?

Accepted Answer

Welcome back. Everyone plotted on the energy diagram below. Our blue and orange curves identify the curve that represents a non spontaneous reaction and a spontaneous reaction we're given first choice A which states that we have an orange curve which represents a non spontaneous reaction. And our blue curve which represents a spontaneous reaction choice B which states that the blue curve is a non spontaneous reaction. And the orange curve is a spontaneous reaction choice C which states that both curbs represent only non spontaneous reactions. And then choice D which states that both curbs represent only spontaneous reactions. Now, looking at our given image and we would notice that we have on our Y axis free energy of our reaction being recorded, which we should recall is represented by the symbol delta G. Whereas on our X axis, we have the reaction coordinate. And so looking at our first curve which is our blue curve, we would find the highest point of our curve being the peak as our transition state. And just before this transition state, we have a lower point which is where our reactants lie on the blue curve. Next, we want to point out a even lower point than where our reactants lie after our transition state in which our products are formed. Recall that the peak of our transition state represents the highest point of energy during our chemical reaction, where our reactants have gained just enough energy to be able to form our products. And so next, let's analyze our orange curve in which we have a peak that is lower than the peak of our blue curve. However, just before this peak, we have a lower point where our reactants lie for our orange curve. And then just after our peak or transition state of our orange curve, we have a higher point than where our reactants lie, which is where our products are formed with all of this outlined. Let's now recall that delta G are gibbs free energy change will help us determine spontaneity of our reaction in which when we have free energy of our reactants being greater than the free energy of our products, we would therefore have a negative gibbs free energy change corresponding to a spontaneous reaction. Next, let's recall that when we have a Gibbs free energy change of our products, which is greater than the gibbs free energy change of our reactants, we therefore have a positive gibbs free energy change corresponding to a non spontaneous reaction. And this means that energy must be absorbed by our reactants in order for the reaction to begin. So focusing first on our blue curve let's show our gibbs free energy change in which we would begin by drawing a dotted line from where our reactants lie to a dotted line to where our products lie and drawing an arrow between these two dotted lines. This would represent our, gives free energy change delta G. And we can see that for our blue curve because our reactants have a higher free energy than our products. We have a negative gibbs free energy change, meaning that our blue curve represents a spontaneous reaction. Whereas our orange curve looking at our orange curb and drawing a dotted line from where our reactants lie as well as a dotted line from where our products lie and drawing a arrow between these two lines. We have our gibbs free energy change in which we can clearly see that the free energy of our products is greater than the free energy of our reactants in our orange curb. And therefore, this describes a positive grips free energy change, meaning that our orange curve describes a non spontaneous process and energy must be absorbed by our reactants for the reaction to occur to form our products. And so in this case, we can look at our answer choices and rule out choice D which states that both curves represent a spontaneous reaction. We saw that to be incorrect, we can also rule out choice c because both curves do not represent non spontaneous reactions. And we can also rule out choice B which incorrectly matches our blue curve as a non spontaneous reaction. And our orange curb as a spontaneous reaction that leaves us with choice A as the only correct choice where our orange curve represents a non spontaneous reaction. And our blue curve represents a spontaneous reaction. So I hope that this made sense and let us know if you have any questions.

Two curves are shown in the following energy diagram:

b. Which curve represents the spontaneous reaction, and which the nonspontaneous?

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Key Concepts

Free Energy

Spontaneous Reactions

Energy Diagrams