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# 6.4: The Second Law of Thermodynamics

## TS Process Diagrams

We have spent a lot of time with $$PV$$ diagrams because they so clearly relate to the work done in a process through the area under the curve. We have also looked at a number process diagrams that involve two other state variables. Now that we have added entropy to our arsenal, it's time to get it in on the action. Returning to our original motivation for introducing the entropy – as a way of creating an integral for heat analogous to that for work, it comes to mind that a $$TS$$ process diagram can do for heat what $$PV$$ diagrams do for work.