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Ch.19 - Chemical Thermodynamics

Chapter 19, Problem 4

Predict the signs of ΔH and ΔS for this reaction. Explain your choice.

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welcome back everyone. What are the signs of our entropy change? And entropy change for the process illustrated below. And justify your answer. So looking at our illustrations, we begin with individual molecules which are not connected and randomly distributed in space. Where we then in our second illustration seem to have formed even larger molecules which have a total of two of our darker colored atoms and two of our white colored atoms which joined together to form this entire structure here. So we would confirm that because we appear to have had bonds formed here on the product side of this process. That is illustrated below, we would recall that bonds formed means we have a entropy change. That is going to be negative, meaning that this is an exact thermic change when bonds are formed. We also want to recognize that as we stated, we went from a smaller or sorry, a larger amount of these individual molecules here to a lower amount of these larger molecules once the bonds formed between each of our smaller units. And so we went from larger amounts will stay here larger amounts of dispersed molecules. They're randomly distributed to fewer molecules and less disorder as a result on our product side. And so we would recognize that entropy is our measure of disorder. And if we have less disorder on our product side, we would agree that therefore entropy decreases. And so we have an entropy sign, that is also going to be negative. So for our final answers, we can confirm that our entropy change is going to be negative because we have bonds formed in an exotic thermic change, and our entropy sign is also going to be negative because we have on our product side fewer molecules meaning less disorder and ultimately a decrease in our entropy measurement. So negative DELTA US and negative delta H. R. Our final answers. I hope everything I explained was clear. If you have any questions, leave them down below and I'll see everyone in the next practice video.