### Why do exothermic processes tend to be spontaneou…

03:23
California State University - East Bay
Problem 13

Explain why water spontaneously freezes to form ice below $0^{\circ} \mathrm{C}$ even though the entropy of the water decreases during the state transition. Why is the freezing of water not spontaneous above $0^{\circ} \mathrm{C} ?$

See explanation.

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## Video Transcript

explain what weathers spontaneously freeze to form eyes below zero degrees Celsius. Even though entropy off the water decreased during the state transition. Why is the freezing water is not spontaneous above zero degrees Celsius? Too soft for this. We want to understand what is spontaneous and what has had to do with entropy. So for this question, whereas a spontaneous to be spontaneous and true P aul, I'm gonna use as in this case, Delta as need to be positive. We also need to know that definition off doctor s. What does that mean? Delta asked is gonna be equal to the delta as off the system. Plus, Delta s off there so wrong. Okay, um, so in this case, the question is saying the freezing off the water by the freezing, the at a lot of freezing, which is going from the liquid to the solid is and true. P wise is decreasing, right? Entropy is decreasing. That sort of say so. What is that saying? That's what is the saying. Is delta as off this system is negative? Okay, so that's what it was. A so freezing water. Water. Entropy is negative. So how exactly it is gonna be spontaneous. Well, um is spontaneous because Delta, as off the universe is positive. Okay, so how is this possible? Well, let's see. Does it? As of system in this case is negative, but we're gonna add it with some positive. Bill likes this. Romney is positive. Alex, if this around me positive value right is big enough bigger than this, then my delta asked all the universe could be positive. And if the as a universe positive, then it's gotta be spontaneous. So let's see how exactly that's cool happened. Two So far, you have actually s off the system. I'm just gonna write it s system. Plus as off this a Roni. Okay. So as if the system is we said, Oh, Raisa is gonna be negative. So you're gonna say native Plus, we said this is positive, but what is the as off the salami, as also surrounding can be solved by doing this. Negative. Dr. H H, by the way, is entropy divided by T. Okay, where's the eight come from? Ages envelop. OK, which is the heat release by, um, by the system when the reaction happened. So in this case, this part the Delta H in this case, going from the liquid to solid stage. Well, make your dove the age to have a negative L Because this is the ah sa thermic reaction. So this is gonna be negative, Ellie, what's gonna happen? Well, negative time negative. This next guys is gonna make it positive. No. So that means if is, temperature is less than zero. This stuff this system plus surrounding would be equal to a positive number. Many is. The answer is gonna be greater than zero. Okay, now what happened? When the temperature is less than zeros on Moreau, a different color pens a switch to this. If the temperature is greater than zero, if the temperatures greater these air, this bottom value is gonna increase. Right. So what is happy if this one barely over to increase is this warm belly were to increase. This s around me. Is gonna read decrease. Okay, So entropy off the surrounding is gonna be decreased. That this order nous that is going to decrease systems. Other change, because system is a state matter so solid to liquid, it's not gonna change. Okay, So you're negative. Us attracting to value where one of them's a minus. One of them's gonna plus, if this number doesn't change but this number to decrease that mean my overall daughter as off the universe is going to become likely to be less than zero. Therefore, it is not gonna be spontaneous. Okay, so the easy and so to that it would you say about this part? Uh, Why? Why the water Not frieze above zero. Okay, so the reason for the water not free. Let me type that up for us. So water do not, does not spontaneously free. All right, spontaneous. Let me retire. That spontaneously. Freeze about zero is because the and true P o it's around or disorder will decrease as t increase does. Is it entropy off the universe? Welby degrees, which in this case was happened, is gonna read, um, daughter as the universe is gonna become less than zero, which mean not spontaneous. That's the reason why. All right, happy study