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### Find $\Delta S_{\mathrm{rxn}}^{\delta}$ for the c…

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University of Massachusetts - Lowell

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Problem 37

Find $\Delta S_{\text { rxn }}^{\circ}$ for the reaction of nitrogen monoxide with hydrogen to form ammonia and water vapor. Is the sign of $\Delta S_{\mathrm{rxn}}^{\circ}$ as expected?

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## Video Transcript

so problem 37 Ask us to find the Dota esri A reaction of the fallen reaction isn't since April a reaction. This is the reaction between nitrous oxide are measured You're not not your monoxide in hygiene. Guess which you It's ammonia gas, ammonia and gashes Water. And it s what are too determined to see if if the sign calculated is exactly what we expect. There is a sign that is that we expect of the Delta X. So to start off we have a reaction here that they give us will be given words, but I translated it too. Thats following equation Eso One thing to note is that this is not balanced. So you gotta balance that which should be No, no big here. Right here. We have to Moore's of nitrogen oxide. Um Teoh Finals with cash is hatching gas. Two moles of ammonia and two moles of cash is water. So now at this point, we can determine this, um waken find out or weaken to term for ourselves. What can we expect from the delta s reaction? It would be positive. Would be negative is an increasing strippers decrease entry. So let's start off with this eso things. They're all gases. So less That's very nice. Makes things a lot simpler. Um, So, um, all we gotta do is just kind of we have to turn where we have more. Also guests. So we have seven most of gas here, and we have foremost begins here. So, community, that is the decreasing was from 7 to 4. That's we have a decrease in entropy. Okay. Unless and our delta s reaction, we it should be negative. It should be in the based off for equation. It should be negative right here. Okay, It's gonna hopes. Okay, it's calculated. Um, we simply just kind of take products minus reactions. So we have a product on left side here off selling one side. Anyways, there are products over here and your reactions over here. I think about the numerical values for the, uh, for the standard Moeller entry piece of each of each compound. Because sometimes that various between where do you source them? I source mind book. Um, but sometimes people outsourcing differently, and sometimes I might have copying to douse covering them down broke, so I just had the value are Have you find values for yourself. Just the concept concept is right here. I just have a concept for you. So I have two moles, I two moles of water. That is the question that I have to, uh, two times the delta s, um, or the standard molar entropy off gashes, water emphasis on gashes. Water it. We don't want liquid water. We don't want salted water. Otherwise, that would screw up our values and our calculation. Because solids, liquids and gases they have different entropy values between the same substance. So am I emphasise gas here. And similarly, I two for ammonia, five for ah, and these are reactions. So we have five for hedging asked, and two for ah, mention mention Minahasa and subtract them. Obviously, because this is our reacted and every actions they become, we noticed the change. We seek their products and we have. There are reactors and we find the difference. The change and where in the total entropy of the reaction and give you crunch the numbers. This is what I got. I got negative 3 10.86 jewels per moles. Calvin drew from road killing emphasis on Jules. And now there's so there are some people that find in unity noise. Sometimes I find the tedious and not. But this is very important having thing unions, especially for a lot of Dermot and Emma, values the units for the entropy values. Though they are always in jewels per mole kelvin for the other thermodynamic values, we have killer jewels. So when you're doing calculations that gives free energy or very worth and GOP, those are always think illegible. So whenever your king. But you're using killed area, entropy and, uh, and and should be at the same time yet to convert one of them TOC jewels or to comfort NDP the jewels. Or you convert potentially to kill the jewels. So note we have a negative value here. So in that aligns with what we predicted earlier because we have. Like I said, it's decreasing more gas 74 in this case, it's just happens to be three negative 310 jewels per mole