What does a particle reservoir mean in thermodynamics? How is it characterised? Heat reservoir for example, is characterised by temperature and supplies or absorbs any amount of heat without changing its temperature. On similar lines, how does a particle reservoir act?


A particle reservoir is a system in chemical equilibrium which is so large that one can extract particles from it without changing its chemical potential. As you see it is quite similar to the heat reservoir.


Note that there is also something called a volume reservoir, acting in the same way (changing volume without affecting pressure). In the literature if all 3 apply, they are called a reservoir in thermodynamic equilibrium. Important to note is that interactions are not allowed to take the reservoir out of its equilibrium state (thermal, mechanical or chemical).

  • $\begingroup$ Why bring in chemical potential or chemical equilibrium? Can we not have a particle reservoir of ideal gas at a given value of temperature and pressure? I would like to draw particles from and supply particles to, it. Can we do that without changing its temperature and pressure? $\endgroup$ – Radhakrishnamurty P Mar 19 '16 at 15:16
  • $\begingroup$ By definition a particle reservoir is characterized by chemical equilibrium with a chemical potential. In physics it has not always to do with chemical reactions, just a matter of terminology. You have to remember that a reservoir also needs a system in contact with it so that they can interact. Thus, you can have a particle reservoir at constant temperature and pressure but then it is also a heat + volume reservoir. So, a system at constant volume in contact with a reservoir exchanges energy and particles with the reservoir without disturbing the reservoir. Use the grand canonical ensemble. $\endgroup$ – user99334 Mar 20 '16 at 16:16

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