Talk:State function

Magnetic field

Is magnetic field also a state function? I feel it should be, but am hesitant to add it since I may be missing some subtlety. Also, the manner in which Markov properties are related to state functions is unclear to me, either from this article or the other. Perhaps this should be clarified or omitted.144.213.253.14 02:21, 31 August 2005 (UTC)

Political meaning

I think it's worth adding a disambiguation for non-native speakers of the meaning of the term "state function" in contexts such as "Here is a picture of the Vice-President at a state function." Any ideas where such a disambiguation should point? A {{wiktionary}} link would probably be the best solution, if Wiktionary had an entry for state function. --Quuxplusone 16:06, 19 January 2006 (UTC)

Poorly defined

As I find with most things relating to chemistry, this is a poorly defined term and its vaugeness and ambiguity lead to the inherint wishy-washyness of chemistry. I remember finally understanding what a "state function" was, but I've forgotten my revelation. This page should note some functions that *are not* state functions. I really can't think of anything. Perhaps... is work not a state function.. I'm not sure. Does "state function" mean that only the absolute spatial distance matters, or can the "path" something takes go through other parameters (for example, time, or energy)? Is there anyone knowlegable about this that can unambiguously explain "state function" and what functions its different from. Fresheneesz 10:10, 4 April 2006 (UTC)

According to Willard Gibbs, W and Q are not functions of the state of the body, where as V, P, T, U, and S are, but instead are determined by the whole series of states through which the body is supposed to pass. I hope this helps?--Sadi Carnot 02:43, 18 July 2006 (UTC)

Page move proposal

My intuition tells me that this page should ideally be moved to Functions of state. From my experience, this is the most commonly used term. Any comments?--Sadi Carnot 02:43, 18 July 2006 (UTC)

Done. — Preceding unsigned comment added by Elnsbrook (talk • contribs) 21:00, 17 June 2011 (UTC)

Chemcial potential

Isn't this quite an important omission form the list of state functions? Initially I thought I must have been mistaken, and that it isn't one, but then it also appears to be in another list in the box in the top right-hand corner — Preceding unsigned comment added by 131.111.185.74 (talk) 11:36, 1 November 2011 (UTC)

State, not parameter.

The section Functions of state Overview makes frequent reference to functions of state as parameters. They aren't, they are states, they describe the system. Parameters in thermodynamics can be constants such as the Boltzmann constant; the value of the Boltzmann constant (the specific thermal energy of a particle) may be given in terms of Joules/Kelvin; Ev/^oR etc. etc. and it is necessary to ensure that there is consistency with the variables (arguments) used in the equations. But the Boltzmann constant is not a variable, it only relates the variables. --Damorbel (talk) 08:59, 17 January 2013 (UTC)

No. State variables are not "states". A "state variable" is something like entropy, pressure, volume; whereas a (macroscopic or microscopic) "state" of the system is something that corresponds to a full macroscopic or microscopic description of the system, such that different descriptions correspond to different states, and vice-versa. Jheald (talk) 21:19, 17 January 2013 (UTC)

Opening statement

The opening statement contains the assertion:-

'A state function describes the equilibrium state of a system.'

This is far from correct. The system does not have to "be in equilibrium" to have properties such as, internal energy, enthalpy, and entropy, as the article says.

This may appear trivial to the uninitiated. But, for example, a system only achieves maximum entropy when in equilibrium. However it still has a (lower) entropy before achieving equilibrium. --Damorbel (talk) 10:11, 17 January 2013 (UTC)

The point of a state function is that it is determined uniquely by the macroscopic variables.

But it is only the equilibrium state that that is true for. There may be many non-equilibrium states with the given values of volume and pressure, and it is not clear that temperature has a well-defined meaning at all for a non-equilibrium state. Jheald (talk) 13:04, 17 January 2013 (UTC)

...determined uniquely by the macroscopic variables. Only true for extensive variables such as energy and entropy. Not remotely true for intensive variables unless the system is in equilibrium. Even entropy can only be determined easily for systems with carefully identified (dis)equilibrium e.g. System 1 at T₁ and System 2 at T₂. These conditions normally occur only in the heads of university lecturers and their textbooks! --Damorbel (talk) 13:35, 17 January 2013 (UTC)

What I mean is that if S is a state variable, you expect (at least locally) to be able to define S=S(V, T, P ... ), so that expressions like ∂S/∂V, ∂S/∂T, ∂P/∂S etc all make sense. If you start getting into the general world of non-equilibrium systems, that can get quite tricky, as the macroscopic variables V, T, P ... may no longer be sufficient to define S (and there may be troubles with the definitions of T as well). OK, it might still be possible for composites of equilibrium systems to total up the state functions of the parts. But that's a special case. It's very different from implying that for any general non-equilibrium state, that you can produce sensible well-defined values for the things you want to be state functions. Jheald (talk) 21:34, 17 January 2013 (UTC)

I'm awfully sorry, but I do not see, from what you write above, any justification for using the word "parameter" instead of "state" or "state variable". It would be a lot clearer if your argument centered on this, the reason why I scrapped "parameter". --Damorbel (talk) 07:38, 18 January 2013 (UTC)

See the reply to the previous section. A "state" has a particular meaning in thermodynamics. It implies a particular value not for one of the variables, but for all of the variables. In the Overview section, parameter is being used as a synonym for variable, which is reasonable. "State" is not a synonym for variable, or even variable value, so your change was not appropriate. Jheald (talk) 10:15, 18 January 2013 (UTC)

State Functions List

Is path independence the only criteria for appearing on this list?? In all my engineering physics courses, altitude has never been presented as a state function in a thermodynamic context. Since altitude in thermodynamics fixes two other independent quantities, namely temperature and density, it shouldn't exist in this list. More fitting would be electromagnetic (potential) fields or location in a gravity field (which BTW is different from ALTITUDE which has an atmospheric context...)

My ludicrous suggestions for additions to this list are meant to draw your attention to this issue. Altitude is NOT an independent thermodynamic state. Indeed your 'altitude' as used in thermodynamics requires knowledge of the atmosphere. Please keep in mind that the link in "Altitude" takes you to an aeronautical/atmospheric description.

Loose paraphrase from my (well-known) thermo text: "if gravitational effects are to be considered, the variable z must be taken into account" VARIABLE Z IS NOT AN ALTITUDE IT IS DISTANCE FROM CENTER OF MASS OF MY GRAVITY PRODUCING OBJECT

kthxbye

sorry if this list was compiled by some professor or authoritative figure, but altitude is literally not the right word here.