Free energy Definition and 302 Threads

The thermodynamic free energy is a concept useful in the thermodynamics of chemical or thermal processes in engineering and science. The change in the free energy is the maximum amount of work that a thermodynamic system can perform in a process at constant temperature, and its sign indicates whether a process is thermodynamically favorable or forbidden. Since free energy usually contains potential energy, it is not absolute but depends on the choice of a zero point. Therefore, only relative free energy values, or changes in free energy, are physically meaningful.
The free energy is a thermodynamic state function, like the internal energy, enthalpy, and entropy.

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  1. S

    Nonlinear Fluid Dynamics & Free Energy Flow

    Hello, I am working on non linear fluid dynamics with my professor. We are trying to model multiphase flows of immiscible fluids. And my professor today asked me to look up works on 'free energy flows', but I cannot find anything on the internet that I can use, let alone understand. Can someone...
  2. stevan

    Double use of energy ? possibility of free energy ?

    I build simple electronic like this picture...
  3. N

    What is the relationship between exergy and Gibbs free energy?

    Hi. I have two questions: 1) Is -ΔG the amount of useful work a system can do while the pressure and temperature of the surroundings are constant? 2) Is exergy = -ΔG only if the pressure and temperature of the system and surroundings is constant? thanks
  4. S

    Imaginary free energy and decay rate

    In euclidean quantum field theory, the imaginary part of the free energy, defined as the logaritm of the partition function, is it connected to the decay rate?
  5. E

    Free energy changes in a canonical ensemble

    I have a question that has puzzled me during the last couple of days. Suppose that there is a system (e.g. a small box filled with gas) that is connected to a heat bath (much larger than the system) at a constant temperature T. The studied system and the heat bath are thought to be isolated from...
  6. F

    Free Energy: Determining Greater Reactants

    This question came to mind when studying voltaic cells. In voltaic cells, for some ions (Cu2+ for example), both oxidation and reduction are possible. Given both possiblities, how do we determine which reaction will take place? I first thought that comparing the signage in voltage of both...
  7. B

    Gibbs Free Energy A Measure of Stability

    Hello everyone, I am having a little difficulty understand precisely what Gibbs free energy is. I have read in my textbook that a negative change in Gibbs free energy implies that the substance under consideration will react/change spontaneously. As such, the more negative the Gibbs free...
  8. S

    Why do Gibbs free energy values change with temperature?

    I calculated some gibbs free energy values for a chemical reaction at 298K and 1773K both giving me negative values . the amount for the reaction at 298K is -162443J and the one at 1773K is -81147.85J. Both shows that the reaction are spontaneous and so thermodynamically the process at 298K is...
  9. N

    Is Constant Temperature Required in the Proof of Helmholtz Free Energy?

    http://en.wikipedia.org/wiki/Helmholtz_free_energy#Work_in_an_Isothermal_Process_and_Equilibrium_Conditions Hi. In the proof that dw <= -dA for isothermal work, where is it assumed T must be constant during the whole process?
  10. kq6up

    Why Is My Calculated Keq from Gibbs Free Energy So Far Off?

    Just for kicks. I tried calculating Keq from Gibb's free energy. This should be a straight forward calculation, but the answer is no where near close. Here is my calculations in SAGE: sage: R=8.314; T=298; G=237000 ; Keq=var('Keq'); f=G+R*T*log(Keq) sage: f.solve(Keq) [Keq ==...
  11. A

    Enthelpy ,gibbs free energy, helmholtz free energy

    To analyze what does the enthalpy, gibbs free energy and helmholtz free energy are used?What is actually meant by usable energy?
  12. A

    What is the difference between gibbs free energy and activation energy

    what is actually meant by gibbs free energy and what is the difference between gibbs free energy and activation energy?In an enthalpy diagram how can it be denoted(just like for activation energy is denoted by the energy difference between transition state and reactants' enthalpy)?I just search...
  13. M

    Exploring Free Energy Change: ΔG, ΔH, and ΔS

    If ##ΔG_{sys} = ΔH_{sys} - TΔS_{sys}; ΔS_{sys} = \frac {-ΔH_{surr}}{T} ## Then, doesn't this expression just simplify to: ##ΔG_{sys} = ΔH_{sys} + ΔH_{surr}## and isn't ##ΔH_{sys} = -ΔH_{surr}##? So then ##ΔG = 0##...this does not seem correct...could anyone please clarify my mistake and...
  14. A

    Atom Energy in Crystals: Gibbs Free Energy

    Does atom at the surface of a crystal have more or less energy than those in the bulk? And how does this relate to their Gibbs free energy?
  15. I

    Gibbs free energy and enthelpy relationship

    *to moderators: i apologize about the double post, but i didn't know how to get rid of the other post and i wanted a get an answer asap and no one was answering the other post so i reposted here in the appropriate section* enthalpy is the energy available if a system with some defined volume...
  16. I

    Gibbs free energy and enthelpy relationship

    ***i just realized that i posted this in the wrong section; could a moderator perhaps move this thread to the classical physics section please? Sorry for the trouble*** enthalpy is the energy available if a system with some defined volume were to be annihilated and have the atmosphere...
  17. Kelsi_Jade

    Helmholtz free energy of simple solid

    The problem is : a) Find Helmholtz free energy F(V, T) of a simple solid. b) Use the result of part a) to verify that (∂F/∂T)v and (∂F/∂V)T are consistent with S(T, V) and P(V, T) in equation P=a0T-b0ln(V/V0) I know: Helmholtz free energy is F=U-TS and dF=-SdT-PdV S=-((∂F/∂T)v)...
  18. C

    Calculate Delta G & Delta H of N2+3H2=>2NH3

    Homework Statement When gaseous nitrogen and hydrogen are converted to gaseous ammonia, then delta G equals: -16.64Kj/mol 3h2+ n2=2nh3 Using the s values , calculate the delta h for the formation of ammonia Homework Equations Delta s for: H2:130.6 N2:191.5 Nh3:192.5 T= 298...
  19. I

    Gibbs Free Energy: Work in H-TS Explained

    the gibbs free energy is defined to be H-TS. In my thermo book, it says that if i were to create a system out from volume V=0 at constant pressure and temperature, the work that i would need to provide is G=H-TS. But for constant pressure i thought the work terms in enthalpy canceled out and...
  20. S

    Gibbs Free energy vs Gibbs Free energy at standard state

    ΔG° is the measure of Gibbs Free energy change at 1 bar but no specified temperature and also the stoichiometric amounts depending on the equation of the chemical reaction. For example, if X ->2Y then the ΔG° would be equal to ΔG°f(2Y)-ΔG°f(X). While for ΔG it is a general term for Gibbs Free...
  21. S

    What is the significance of Gibbs Free energy change in chemical reactions?

    In reaction there is a Gibbs Free energy change. I'm still not sure what this means as in my secondary school years we just learned of one component of it which is the enthalpy change. That was simple as it just showed how much heat was released or absorbed. But with Gibbs Free energy, i don't...
  22. Useful nucleus

    Gibbs Free Energy and the Grand Potential

    Gibbs Free Energy is the appropriate potential when there is both heat exchange and mechanical work (G=E-TS+PV). On the other hand the grand potential is appropriate when there is heat exchange and chemical work (g=E-TS-μN). Is there any issue in defining a potential of the form (E-TS-μN+PV)...
  23. C

    Find an Expression for the Helmholtz free energy

    Homework Statement I am attempting the problem below, I might have the correct answer but would appreciate if someone could confirm this (or tell me where I'm going wrong). Consider a statement having 2 states, one at energy 0 and one at energy ε. Find an expression for the Helmholtz free...
  24. S

    Gibbs free energy going to zero (equilibrium)

    Hi I have a 4 part question about phase changes and I hope you guys can help me out here thanks :) The chemical equation for vaporization for water is H2O(l)-->H2O(g) 1) When ΔG is 0 during a phase change we would use the formula ΔH=TΔS and put in values to get the boiling/melting point by...
  25. S

    Rumors surrounding Tesla's free energy

    So reading on his work I stumble upon him wanting to give everyone free energy. This video shows how it could work. But mythbusters did a program on this where they say it's not possible. I'm not asking about creating energy but just if it's possible like how Tesla wanted to get energy...
  26. electricspit

    Gibbs Free Energy and Equation of State

    I'm wondering why the Gibbs function is related to the equation of state as follows (supposedly): V=(\frac{∂G}{∂P})_T I found a thread on here that mentions this relationship, but doesn't explain it at all. Any help understanding this would be appreciated, this is my first introduction to...
  27. S

    Gibbs free energy and the first law of thermodynamics

    Hi thanks for reading. I have 2 questions regarding the topics mentioned that I'm having trouble with. Hope you guys can help me out here :) 1) The first law is ΔU=Q+W so we can rearrange this to get ΔH=ΔU+PΔV so would this indicate that ΔH only measures the heat given out at constant...
  28. Z

    Quick question about Gibbs free energy

    In the expression defining Gibbs free energy, G = U - TS +pV, are T and p the temperature and pressure of the environment, or of the system itself? Or is it a requirement that the system has the same temperature and pressure as the environment for the Gibbs free energy to be defined?
  29. D

    Temperature CONFUSION in derivation for Helmholtz Free Energy

    Dear all, I have been spending 12 hours on this and cannot seem to come up with a solution. We derive Helmholtz Free Energy (A) from the second law of thermodynamics. dS(Total) = dS(system) + dS(surrounds) we try to express dS(surrounds) with properties of the system. Assuming...
  30. fluidistic

    Stability, Helmholtz free energy mathematical relation proof

    Stability, Helmholtz free energy mathematical relation "proof" Homework Statement I must show that \left ( \frac{\partial ^2 F}{\partial V ^2} \right ) _T=\frac{\frac{\partial ^2 U}{\partial S^2} \frac{\partial ^2 U}{\partial V ^2} - \left ( \frac{\partial ^2 U}{\partial S \partial V} \right...
  31. A

    Difference between enthelpy, Helmholtz free energy,& Gibbs free energy

    I am study chapter 5 of An Introduction to Thermal Physics by Schroeder and I am having trouble understanding his explanation of the differences between enthaply, Helmholtz free energy, and Gibbs free energy. Schroeder defines enthalpy of a system as its energy plus the work needed to make...
  32. D

    Free energy change during adsorption

    Hi, Suppose I have a dissociative adsorption reaction and want to find the free energy change ΔF, this can be written at constant temperature: \Delta F = \Delta E -T\Delta S Now given the adsorption energy \Delta E_{ads} I would like to extrapolate the Free energy assuming that the adsorbate...
  33. H

    Relation between gibbs free energy and equilibrium constant

    I am familiar with the equation ΔG=ΔG°+RT ln(Q).But I can't derive it.We have to use the equation to derive nernst equation. So please help.
  34. T

    Could a magnetic charge make free energy?

    If or when magnetic charges (magnetic monopoles) are found, would a magnetic current create an electric field? If so, would you be able to generate an electric current with an applied field?
  35. T

    Purpose of natural log in gibbs free energy equation

    Hi,Im just beginner and I m trying to learn integrals.I m just in starting phase,but still in few tences,not details...How or why we get logarithm in gibbs free energy equation?Because of integration of this equation or due to probability and statistics laws? Thanks
  36. K

    Van de Waals fluid in Free energy, Enthelpy representations

    Compute the coefficient of expansion α in terms of P and V... Homework Statement Compute the coefficient of expansion α in terms of P and V for an ideal Van der Waals gas Homework Equations (p+a/v^2)(v-b)=RT The Attempt at a Solution Is this as simple as solving for a? How...
  37. A

    How Does Gibbs Free Energy Relate to Phase Changes?

    Hi, As I understand, during the process of phase change from a liquid to solid (or any phase change for that matter,) the temperature of the substance remains constant as the energy being applied to the substance is used in changing phase. How does this relate to Gibbs free energy? I read that...
  38. J

    Quick question about Gibbs Free Energy

    If this isn't the correct place to ask this, please point me to where I should. I feel there are quite a few guidelines to what can be posted and what cannot, so I hope I don't break any rules! I'm working on a problem, that deals with a superheated steam, that goes from an initial state to...
  39. D

    Gibbs Free Energy of Formation: 1°C or 25°C? (And other exciting questions.)

    Hi there: When using ΔG=ΔG°+RT ln Q to calculate the energy yield of a reaction, does it matter if I use ΔG° calculated at 1°C or 25°C? Also, why are there two choices and when are they each applicable? Finally, I have also seen ΔG°' written (note the prime). What does this mean and how does...
  40. H

    Free energy question involving Kp and deltaG

    Homework Statement The following reaction takes place at standard conditions 4NH3(g)+6NO(g)----->5N2(g)+6H20 A)calculate reaction enthalpy and Gibbs reaction energy B)Calculate Kp Homework Equations the table gives the following values for deltaG0f[X] NH3(g)=-16.5 Kj/mol...
  41. M

    Where Am I Going Wrong in Calculating Free Energy Change?

    Homework Statement In the previous question, you had to calculate the the standard Free Energy Change (Go) in order to solve for the equilibrium constant, K, for the reaction: N2(g) + 3H2(g) → 2NH3(g) This is the Free Energy measured under standard conditions, when the reaction is...
  42. Jalo

    Thermodynamics - Change in the free energy

    1. Homework Statement [/b] Consider a Van der Waals gas. Consider a recipient of volume 2V, with a mobile wall (with no friction) that divides the recipient in two, each part having exactally N particles. The system is at equilibrium and the mobile wall is exactally in the middle of the...
  43. Jalo

    Thermodynamics - Change in the free energy

    Homework Statement Consider a Van der Waals gas. Consider a recipient of volume 2V, with a mobile wall (with no friction) that divides the recipient in two, each part having exactally N particles. The system is at equilibrium and the mobile wall is exactally in the middle of the recipient...
  44. B

    Thermodynamics-Gibbs free energy: what can we actually measure in the lab?

    Thermodynamics--Gibbs free energy: what can we actually measure in the lab? Hi everyone: I am getting back into thermodynamics after a long absence and have realized that there are basics I have never understood. If a patient person could either explain or direct me to an online resource...
  45. A

    Helmholtz free energy related query.

    hello This is a section from Callen, Herbert B - Thermodynamics and an Introduction to Thermostatistics "Any equilibrium state can be characterized either as a state of maximum entropy for given energy or as a state of minimum energy for given entropy. But these two criteria nevertheless...
  46. B

    Temperature analog of free energy

    The Gibbs energy is used to determine the spontaneity of a thermodynamic process under isobaric conditions. The Helmholtz energy is used to determine the spontaneity of a thermodynamic process under isovolumetric conditions. I was curious: is there an energy used to determine the spontaneity...
  47. L

    Stat phys - free energy from eq of state

    Homework Statement Consider a mixture of hard spheres of diameter σ. The potential energy for a hard sphere system is given by \beta U(r) = 0 (r > \sigma) ∞ (r ≤ \sigma) The packing fraction (η) of the system is the amount of space occupied by the particles. (b) The...
  48. M

    Elasticity, free energy of isotropic body mismatch

    I'm looking at the free energy of a body (theory of elasticity) but I can't really square the general expression with the one usually used for isotropic bodies. According to wikipedia (http://en.wikipedia.org/wiki/Elastic_energy), Landau & Lifgarbagez etc the general expression for the free...
  49. A

    Statistical Relationship Between Helmoltz Free Energy and Entropy

    Homework Statement From Hill's "Introduction to Statistical Thermodynamics", question 3-4 reads: (note "STR" denotes the case of most probable distribution and should be read as C*) Homework Equations The most probable distribution for a system of independent indistinguishable...
  50. S

    Is the Helmholez or Gibbs free energy every used outside of reactions?

    I'm trying to figure out if the Helmholtz & Gibbs free energy are ever used outside of chemical reactions (I suppose they could be used in nuclear reactions in a plasma as well.) It seems to me that they are not, as I can only recall using them for chemical reactions in my thermodynamics course...
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