Understand Irreversible & Reversible Processes - Intro to Thermo of Materials

[asdf1]

I'm reading the book, "Introduction to the Thermodynamics of Materials" (4/e) by David R. Gaskell. There's a section on pg42 explaining irreversible and reversible process, but I have no clue what the point is... Can someone explain it, please?

 

[Pengwuino]

I really doubt your going to get an answer. You probably should copy down whatever is troublesome for you and post it here.

 

[FredGarvin]

Reversible process = no entropy production. Or to put it another way, you can turn the process around and go back to the exact same condition that you started with. You can think of it as the process that will be the best (theoretically) you can hope for. A reversible process means that to go from state 1 to 2, the process has to happen very slowly so that equilibrium is reached at every small step.

 

[asdf1]

does the work always equal 2PV? I think that's what the textbook is trying to say...

 

[FredGarvin]

Work is the area under the curve on a P-V diagram.

 

[minger]

does the work always equal 2PV? I think that's what the textbook is trying to say...

In order for work to be done, there must be a change in volume. Because of this, 2PV doesn't really mean anything. Take a reversible process at constant pressure. Imagine a piston-cylinder set up. The volume is slowly increased as to keep the process reversible and to keep pressure constant. Now, if you draw the process on a P-v diagram, it will be a straight (horizontal) line. The work can be calculated by integrating [or since its a rectangle, P(v2-v1)].

 

[asdf1]

:) i understand now~
thanks!