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Fluids

Isobaric process

Let us return to the isobaric process which is represented by the figure below.



We already saw that while the ideal gas under a freely movable piston was heated, it produced work given by

W_1→2 = P×ΔV = P×(V₂-V₁)

Now, we can also determine the increase in the total kinetic energy E_kin(1→2) of the amount of gas, namely

E_kin(1→2) = 3PΔV/2 = 3P×(V₂-V₁)/2

Total energy conservation gives us now a clue about the total heat Q_1→2 which must have been delivered to the gas in order that it could increase its total kinetic energy and, moreover, deliver work. We conclude from total energy conservation that Q_1→2 must be equal to the sum of the two forms of energy:

Q_1→2 = E_kin(1→2) + W_1→2 = 5P×(V₂-V₁)/2

From the above expressions it is clear that heat has the same unit as kinetic energy and work, namely 1 Joule.

We found out how much heat is necessary for the work needed for machines to run.
However, in order for the machines to keep running, the above process has to be repeated. In the following we will find how that can be achieved.

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