What is Thermodynamic potential: Definition and 12 Discussions

A thermodynamic potential (or more accurately, a thermodynamic potential energy) is a scalar quantity used to represent the thermodynamic state of a system. The concept of thermodynamic potentials was introduced by Pierre Duhem in 1886. Josiah Willard Gibbs in his papers used the term fundamental functions. One main thermodynamic potential that has a physical interpretation is the internal energy U. It is the energy of configuration of a given system of conservative forces (that is why it is called potential) and only has meaning with respect to a defined set of references (or data). Expressions for all other thermodynamic energy potentials are derivable via Legendre transforms from an expression for U. In thermodynamics, external forces, such as gravity, are typically disregarded when formulating expressions for potentials. For example, while all the working fluid in a steam engine may have higher energy due to gravity while sitting on top of Mount Everest than it would at the bottom of the Mariana Trench, the gravitational potential energy term in the formula for the internal energy would usually be ignored because changes in gravitational potential within the engine during operation would be negligible. In a large system under even homogeneous external force, like the earth atmosphere under gravity, the intensive parameters (


{\displaystyle p,T,\rho }
, i.e. pressure, temperature, and density respectively) should be studied locally having even in equilibrium different values in different places far from each other (see thermodynamic models of troposphere).

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  1. cwill53

    I Change of Variables in Thermodynamics

    I have a question about changing variables in the context of thermodynamics, but I suppose this would extend to any set of variables that have defined and nonzero partial derivatives on a given set of points. First I should define the variables. ##T## is temperature, ##U## is internal energy...
  2. Marcus95

    Liquidification of Helium under constant Enthelphy Condition

    Homework Statement a)Helium enters a closed system as a flow of compressed gas at a temperature of 14 K and at pressure p (enthalpy conserved). A fraction α emerges as liquid and the rest as gas at 14 K, both at atmospheric pressure p0. Find an expression for α in terms of the enthalpy H(p) of...
  3. H

    Work done for isothermal process in terms of Helmholtz func

    The Helmholtz function differential form for a reversible process is: dF = -SdT - PdV, as for a reversible process δW (by system/here an (ideal) gas) = PdV and dS = δQ/T. Therefore, for a reversible isothermal process, dT = 0 and hence dF = -PdV. Therefore, the work done by the system is W =...
  4. G

    Show ##(\frac{\partial S}{\partial G})_Y = -\frac{C_Y}{TS}##

    Homework Statement Show that ##(\frac{\partial S}{\partial G})_Y = -\frac{C_Y}{TS}## Homework Equations ##G = H-TS, (\frac{\partial H}{\partial T})_Y = C_Y## The Attempt at a Solution ##dG = dH -TdS -SdT## and ##H## is a state variable so ## dH =\frac{\partial H}{\partial T} dT +...
  5. U

    Thermodynamics: Enthelpy vs. Gibbs Free Energy usage

    I'm currently taking a Biophysics lecture. There's a vast usage of the terms Enthalpy and Gibbs Free Energy. I understood that most of the time, we're dealing with the Gibbs Free Energy, because our experiment is at constant Temperature (e.g. room temperature) and constant Pressure (e.g. 1 atm)...
  6. mef51

    [Thermodynamics] Temperature change during cooling of a gas

    Homework Statement One method for cooling a gas is adiabatic throttling (Joule-Thomson Experiment). Another method is a reversible adiabatic expansion. Show that if the initial and final pressures are the same, the difference in temperature obtained by the second method is always higher. Hint...
  7. M

    Thermodynamic potential and energy density in cosmic models

    I'm reading this paper http://arxiv.org/abs/0911.1728 It's about the authors' consideration of the Mass Varying Neutrino model with a new approach that try to explain the cosmic acceleration then. I often encounter the thermodynamic potential during reading and re-calculating the...
  8. J

    A rather specific thermodynamic potential

    Today, during class, our professor went through a simple example about Piezoelectricity. We have a cylinder with a trapped ideal gas and a piston which is part of a capacitor together with the bottom of the cylinder. The voltage across the capacitor is \Phi, and the charge is Q. The distance...
  9. Y

    What is thermodynamic potential?

    what is thermodynamic potential?
  10. H

    Deriving Helmholtz Thermodynamic Potential & Corresponding Maxwell Relation

    Homework Statement To state the differential form of the Helmholtz thermodynamic potential and derive the corresponding Maxwell's relation. Homework Equations Stated within the solution attempt. The Attempt at a Solution Helmholtz function: F = U - TS Calculating the...
  11. F

    Thermodynamic potential question,help

    i have studied my lecture notes back to front and looked high and low for a clue how to do this question but i tried in a) constructing an expression for u and came up with DU= +TDS -PDV - FDL BAUT I COULD BE MILES OUT. could anyone help. thanks here it goes: A piece of rubber of...