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Problem 51

20.51 Calculate $\Delta G^{\circ}$ for each react…

04:16
Problem 50

How can $\Delta S^{\circ}$ be relatively independent of $T$ if $S^{\circ}$ of each reactant and product increases with $T ?$

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Video Transcript

we want to explain why they changed. An entropy of a reaction or delta s of reaction is largely unaffected by the fact that an increase in temperature it leads to an increase in the standard molar entropy values for the chemical species involved in their reaction. In that, a decrease in temperature also results in a decrease in those values. This is the general equation that we used to find Delta s of reaction. If we consider a generic reaction of reacting, a going to product be and each one of these has a given striking metric coefficient A and B After your we we balance the reaction, then we can use the above equation to write out a qualitative expression for Delta s of reaction, You know that we start with the products we won't apply and the number of moles of a given product by its value in in terms of its standard Mueller entropy again of the products and we subtract Same for the reaction, the reactant. So the story geometric coefficient multiplied by the standard miller entropy of the reactions. And again we were told that these values depend on the temperature. They both increase with increasing temperature and decrease with decreasing temperature. However, when we calculated out, we're told that the value for Delta s of the reaction is not what what under what conditions would it be true that that would not change a lot even though we know that both of these change with temperature? Well, it turns out that the main reason that that we have a small change in entropy of a reaction even though the standard Mueller n trapeze changed a lot with temperature, is the state of matter of the react. In some products, you see that we have a gas phase reaction. So we convert one gas into another gas recall that the general trend is that as we go from a solid to a liquid to a gas, that the entropy of the system increases as gas particles move about randomly and therefore have a lot more disorder compared to solids and liquids. And so there is a certain a certain amount of change and entropy of the system as a result of a chemical reaction, because we have different numbers of moles, of reactions and products and different values of the change in an entropy values that we know are dependent upon temperature. However, from this trend, we know that there is also a a large amount of change in an entropy of of a reaction, converting from one state of matter to another. We go from a solid to a gas, for example. We know that we would have to increase the temperature, which would result in a lot more disorder in the way that those those particles are organized and therefore increase the entropy. However, if we if we stay at one state of matter like the gas phase, reaction illustrated in this example appear than that change in entropy. To go from a solid to a gas, for example, or a liquid to a gas is not is not part of is not factored into this. This total change in entropy of the system. And that's the same whether we have also all solids or an all liquid reaction. It doesn't matter if we have solid liquid or gas, as long as all of the species involved in the reaction are all the same. State of matter. No matter what that state of matter is, then we can expect that even though standard molar entropy is change with temperature that the change in entropy of the overall reaction will be relatively unaffected. So the key is that we have to have the same states of matter involved in the chemical species before and after the reaction. In order for Delta s to not change a lot with with temperature.