Boundary (thermodynamic)

  In heat, mass, or work can flow.^[1] In short, a thermodynamic boundary a division between a system and its surroundings. A boundary may be adiabatic, isothermal, diathermal, insulating, permeable, or semipermeable. Boundaries can also be fixed (e.g. a constant volume reactor) or moveable (e.g. a piston).