In nature almost all thermodynamic transformations are irreversible: coffee cools down, the gas in an aerosol can expands when the valve is opened, a red-hot block dropped into water brings everything to equilibrium. In these cases the gas passes through states that are not equilibrium states, and it makes no sense to draw a curve in the - plane. And yet conservation of energy always works: it is enough to know the initial state A and the final state B, without worrying about the path. This chapter shows how the first law, read as an energy balance with bubble diagrams, solves a wide variety of irreversible problems.
Sections
- Irreversible transformations
- The first law as an energy balance
- Energy exchange diagram
- Three typical problems
- Thermal equilibrium: solid + gas
- Heating at constant pressure: the Cp coefficient
- Mixed problems: pistons, springs, gravity