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Ch 19: The First Law of Thermodynamics
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All textbooksYoung & Freedman Calc 14th EditionCh 19: The First Law of ThermodynamicsProblem 19

Chapter 19, Problem 19

Figure E19.8 shows a pV-diagram for an ideal gas in which its absolute temperature at b is one-fourth of its absolute temperature at a.

(d) Did heat enter or leave the gas from a to b? How do you know?

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everyone in this problem. We are provided with a PV diagram. Okay, we're told that pressure is absolute pressure. The temperature at Y is five times the temperature at X. Now, when moving from Y two X. Brass does a gas gain or lose heat? Okay, we need to give a reason. Alright, well, let's look at this, we're talking about heat. Let's recall that the heat Q can be given by N C delta T. Okay. Now, see as the heat capacity, which heat capacity do we use? Well, looking at our PV diagram, we have a horizontal line between y and X. What that means is that the pressure is constant? The pressure is not changing. So under constant pressure, we're gonna use the heat capacity cp the heat capacity for constant pressure. Alright, so let's work this out or expand a little bit. We're gonna have N time cp. Now, delta T. Is going to be the final temperature. Okay, we're moving from Y two X. So the final temperature is going to be the temperature X minus the temperature at Y. Okay, now, T x minus t Y. Well, this is going to be less than zero. It's going to be negative because we are told that the temperature at y is five times the temperature at X. So, T y is bigger than T X. Ok. Which means that t x minus t y is going to be negative. We know that the number of moles in C p is going to be positive. Okay, so this tells us that Q is going to be less than zero. Okay, If Q is less than zero, that means that we're losing heat. We have a negative heat. We are losing heat. Okay? So we're looking at options either B or C. We're losing key. Why are we losing key? What we just saw in our equation? We're losing key because delta T. Is negative. Okay. And so we're gonna have option C. Okay, We're losing heat when we move from Y two X. Because DELTA T is negative. Thanks everyone for watching. I hope this video helped see you in the next one.
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