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Problem 7

(a) What is the entropy of a perfect crystal at 0…

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Problem 6

How does the entropy of the surroundings change during an exothermic reaction? An endothermic reaction? Other than the examples in text, describe a spontaneous endothermic process.

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Video Transcript

Chapter 20 Problem six is about the entropy of surroundings during the ex atomic reaction as well as the surroundings during Endo thermic reaction. So to review this, let's look at the second law of thermodynamics. This law states that the entropy of the universe is going to be positive in a spontaneous reaction or spontaneous change. And the entropy of the universe is actually equal to the entropy of the systems, plus the inter p of the surroundings. So this is entropy of the universe. This is the intra Pete of the surroundings, plus the entropy of your system. So I have two boxes here. One is representing one universe where there's an extra thermic change. And here is a universe where there's an end of term it change. Let's first think about the extra thermic and XO thermic change. He is released. So in this center area we have our system that where the reaction is occurring and this black box is representing our surrounding saying here we have our system. In the black box is our surroundings and an ex atomic reaction. He is released from the system into the surroundings. Try that again. So heat is being released into the surroundings and an ex a thermic reaction That means the degree of freedom the freedom of the particle motion in your surroundings is going to increase. So when an ex academics reaction, the entropy of your surroundings increases, let's think about an endorphin IC reaction in the thermite reaction requires energy to occur. That means he is being absorbed into the system from the surroundings and therefore heat is lost. The freedom of particle motion here is decreasing as the kinetic energy or the heat is being lost to the system. So because the heat is going into the system, it's leaving the surroundings and therefore the entropy of your surroundings and XO. Thermic system decreases. No, you can still have an ex a thermic an endo. Thermic spontaneous reaction, an example of an endo thermic, spontaneous reaction is if you had a cold pack. Now we know that the heat of this system is increasing for endo thermic, and the heat of the surroundings is decreasing If the heat of the system increases more than the heat of the surrounding increase decreases. Excuse me, then, therefore you can have a positive entropy in the entire system. So in all of the only way for an endo thermic reaction to be spontaneous is if the heat of the system, the entropy of the system increases more than the entropy of the surroundings decreases. An example of that is a cold pack. You have a cold pack. You ever played a sport and fallen, and to prevent yourself from swelling, you put a cold pack on you. When you initially touched, it may have been at room temperature, but when you shake it up, it actually begins to become cold. And this is an endo thermic reaction. Where is taking heat from the surroundings, as well as, um, heat from the water as well? And it's causing an endo thermic reaction where it's becoming much, much colder. So when we makes up an ice pack or essentially breaking the barrier that existed between the water that was initially in there and the male ammonium nitrate. When this breaks, the two particles end up mixing, and your ammonium nitrate breaks into ammonium ions and nitrate ions that are now dissolved. It's a solution, so you're going from a solid to liquid, and that changed to look what is an increase in entropy. So what happens here? We have more particles, more degrees of freedom, as you have one solid here breaking into two things, one being the ammonium in 84. It's a cat eye on in the other being nitrate, you know, three. So you're moving from to particles two compounds into the system into three, and so therefore, you have an increase in entropy here and the system, even though there was a decrease in entropy of the surroundings. And if you put it on the ice pack on your arm, you would feel cold because he does, leaving your arm and moving into that ice pack moving into that system so there's a decrease in the surroundings, but there is such a large increase in the system that it is still a spontaneous reaction.

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