WEBVTT
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welcome to our fourth example video. Looking at the
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first law of thermodynamics in this video, we're going
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to consider our first law, which is change in
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e thermal is equal to Q minus W. And
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we're going to consider it for the processes that we've
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looked at so far. Where we have the constant
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volume, or is a coric the constant pressure,
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or is a barrack the constant temperature or is a
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thermal? We're also going to consider What does it
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mean to have Q equal to zero? Now,
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looking at these situations, you'll remember that work equals
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zero. Here, here, we're going to see
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that we have work is equal to a P Delta
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V. Notice that since we have a change in
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volume, this is going to imply that we're going
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to have a change in temperature. So api Delta
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V is going to be equal to an N R
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. Delta T, and then over here for is
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a thermal process. We have work is definitely greater
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than zero, especially if we're going to the right
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. Specify that as our direction. But we have
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a delta t equal to zero. Okay, so
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let's examine what all these things mean in the first
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case, we have a work that is going to
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be zero. And when we see that work is
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zero, we know that the chain any change in
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thermal energy is going to be equal to some heat
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. So this is heat either added to the system
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it be positive or taken away from the system.
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It would be negative just looking at the direction here
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. We can see that we have a pressure decreasing
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, which would imply that we're losing energy from the
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system. And so we would have a negative que
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here, so Delta e thermal would be less than
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zero jewels. Meanwhile, looking over here for the
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constant pressure process, Theis a barrack process. We
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see that we do have a work and it's going
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over some space here. And so our Delta E
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thermal is going to be Q minus W. And
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because it's going to the right, W will be
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positive. If it had been to the left,
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we would have had minus a negative W. In
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which case we would have had Q plus W as
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our total thermal energy. Remember, if it's to
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the left, that means that his work being done
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on the system. Energy is being transferred into the
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system via mechanical work and the third situation where we
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have a change in temperature that is equal to zero
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. That's the same thing is saying that we're on
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. We're going to be in thermal equilibrium, which
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means we have a zero change in thermal energy,
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which would imply that we need Q equal to our
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work so we can actually calculate the heat transferred in
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this system because it will be equal to how much
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work is done. So if we do it positive
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work by the system, that means we're going to
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be adding this heat here, okay, and lastly
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, we have the situation where Q equals zero again
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, this is known as an idiomatic process will look
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at thes several times as we continue to look at
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all these processes with an added a Batic process.
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It means that any change in thermal energy is going
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to be due entirely to work done either by or
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on the system. Remember, by the system means
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it's positive on the system means it's negative, and
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that will change. Sign for the delta, the
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thermal If the system does work. That means it
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loses thermal energy because we have minus W. If
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we have the system having work done on it,
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that's a negative W and negative times a negative is
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a positive. When we do work on the system
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, there is a positive change in thermal energy for
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the system.