Talk:Thermodynamic system

Extensive property

The property of the system whose value depends upon the amount of substance present in the system is called extensive property for example:- Mass, volume, surface area, enthalpy, entropy,

free energy etc... 2405:201:5001:7C6E:C525:58AE:B129:2570 (talk) 14:36, 30 January 2022 (UTC)

Internal variables

It seems to me that the author himself has no clue what these internal variables are. Weaky3 (talk) 23:51, 25 March 2023 (UTC)

Permeable to matter

What would a thermodynamic system be like that only allows for transfer of matter, but not of energy? (See "permeable to matter" at Thermodynamic system#Walls.) A particle necessarily contains energy because otherwise it could not move, so it could not cross the boundary of the system, and it can't be at 0 K either, for the same reason. Can one cite a source that says that a transfer of substance is possible without allowing the transfer of energy? Turbojet (talk) 05:38, 9 July 2026 (UTC)

I think you're right. I removed it.--Srleffler (talk) 05:27, 10 July 2026 (UTC)

What transfer of energy is encountered in usual or ordinary diffusion through membranes? ~2026-39006-70 (talk) 06:14, 10 July 2026 (UTC)

Thank you.

I apologize, I don't know. My specialty is heat-related stuff (engines, turbines, equipment, etc.). I don't deal with chemistry, electromagnetism, etc. All I know about [semi]permeable membranes is about those in fuel cells, but the cells themselves are not my specialty. And I think what you asked should be treated under chemical thermodynamics, this article should remain about technical thermodynamics, based mainly on Q and W. --Turbojet (talk) 08:54, 10 July 2026 (UTC)

Open or closed systems?

Are the thermodynamic systems where only electricity is transfered (like galvanic cells or batteries) a special case of closed systems? Because no mass transfer occurs, only electricity transfer? ~2026-39006-70 (talk) 07:18, 10 July 2026 (UTC)

If no substance is transferred to or from the environment, for example hydrogen (protons), then yes, theoretically they are closed systems. However, as far as I know, thermodynamic systems only refer to the forms of energy heat and work. Any other form of energy, for example electrical energy, is considered to be transferred beyond the imaginary boundaries of the thermodynamic system (which is an abstract notion, not the concrete physical system) only after it is transformed into one of the above forms. For example, in the calorimeter bomb the electrical energy of the spark that initiates combustion is considered a heat input into the system, not electrical energy. Probably when transferring electromagnetic, chemical, light, etc. energy that is not transformed into heat or work the system should be treated as a physical system, not as a thermodynamic one. Therefore, the notion of a thermodynamic system should not be generalized, but that of a physical system, the thermodynamic one being a subset of it, defined by the two types of energy: heat and work. :) --Turbojet (talk) 11:12, 10 July 2026 (UTC)

Galvanic cells are also thermodynamic systems, according to the works by Gibbs, of electrochemical thermodynamics. Indeed the spark can be treated as heat. Also the mechanical work of an electric motor expresses mechanical energy, but the electric energy provided by galvanic cells or batteries enters as such, electric term, in the expression of the first principle of thermodynamics. What you say about only heat and work refers to simple compressible thermodynamic systems. Galvanic cells are NOT simple compressible thermodynamic systems. ~2026-39006-70 (talk) 12:36, 10 July 2026 (UTC)

Charge is carried by particles that have mass, so if electricity is transferred into or out of a system, the system is not closed.--Srleffler (talk) 02:22, 11 July 2026 (UTC)

But isn't the mass of those particles (usually electrons) very small and thus insignificant/ignorable? ~2026-40005-66 (talk) 13:37, 16 July 2026 (UTC)

Maybe so, maybe not. But since you can only use a battery to do work by connecting it to a circuit, any electron that 'leaves' the battery at the negative terminal is replaced by one 'entering' at the positive terminal, so the mass inside remains the same in any event. MrOllie (talk) 13:43, 16 July 2026 (UTC)

Well underlined. I hadn't thought at this possibility when I was writing the above. ~2026-40005-66 (talk) 14:04, 16 July 2026 (UTC)

The fact that the mass leaving is equal to the mass entering does not mean that the thermodynamic system can be considered closed. Consider a steam turbine. The mass of the steam entering is equal to the mass of the steam leaving, plus any condensate discharges. If they were not equal, the mass entering would accumulate in the turbine, or, more absurdly, the turbine would create mass. From the point of view of mass, the electrons in the battery behave like the steam in the turbine. And "negligible" does not mean "zero". --Turbojet (talk) 16:11, 20 July 2026 (UTC)