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

    Gibbs Free Energy Change/Entropy

    Hi, seen as it's Physical Chemistry I am asking about and Physical Chemistry is essentially applied Physics I figured that it would be okay to ask here. I have an exam this tuesday, and my lecturer went over some seminar questions. He provided answers to the calculations but did not provide...
  2. R

    Question about Gibb's Free Energy and Equilibrium

    for the reaction ATP + H2O -> ADP + H2PO4- Delta(G^0)= -30.5 kj/mol A)if 0.5 mol of ATP, 1 mol of H2O, 1.5 mol of ADP, and 0.2 mol of H2PO4- are mixed in a 2.2L container at 23C, which direction would the reaction shift to reach equilibrium? I used Delta(G) = Delta(G^0) + RT*ln(Q) I...
  3. M

    Vibrational free energy in the high temperature limit

    This doesn't really qualify as a proper physics question, but I don't know where to put this... I have been thinking about this for about 2 hours now, and just don't get the correct approximation. For the free energy of the vibrational degrees of freedom of a diatomic ideal gas I have...
  4. S

    Gibbs free energy doesn't increase (constant T and P) - proof doesn't seem right

    First my notes discover that for an isothermal transformation; ΔW ≥ ΔF Where W is the work done and F is the Helmholtz Free Energy, F = E - TS. Then it defines the Gibbs free Energy; G = F + PV "For a system at constant temperature and pressure, G never increases"; So ΔG = ΔF...
  5. I

    Gibbs Free Energy of Atomic Hydrogen Ionization

    Homework Statement Despite extensive searches of the web and my old honors freshman chem text, I have yet to find a kj /mol value for either the standard Gibbs' Free Energy (Delta-G-naught (298° K)) or standard ENTROPY (Delta-S-naught) for the ionization of gaseous ATOMIC Hydrogen (or for...
  6. C

    Thermochemistry:Gibbs' Free Energy and Entropy

    Homework Statement a) 3 moles of carbon dioxide gas expands reversibly in a piston-container from 20 L to 40 L in an isothermal process at 400 K. Calculate work, heat, change in internal energy and change in enthalpy, considering van der Waals behaviour. [a = 3.59 atm L^2 mol^-2 and b = 0.0427...
  7. O

    Is there any Physicists that think Free Energy could maybe be possible?

    Hello Again, I hope I don't come across as an a@# or worse! I have talked to a couple physicists and when you get to this subject they just shut down. "It is impossible so no more conversation!" I know it has been tried by much smarter people than me. I might look at things differently...
  8. K

    Gravity, Free energy, and proving my pet idiot wrong.

    I have a pet idiot, you know the type. "Perpetual motion is the future, we don't understand everything!" Well we've been discussing gravity, (and magnets, oh how he goes on about magnets). He doesn't seem to be able to see the difference between force and energy. I've finally gotten him to...
  9. A

    Do not understand Helmholtz free energy

    I'm currently learning thermodynamics from Schroeder's "An Intoduction to Thermal Physics". He explains that in an environment of constant temperature, the system can extract heat from the environment for free when we create a system, and the Helmholtz free energy is that additional work needed...
  10. K

    Gibbs free energy from partial pressures

    Homework Statement Consider the following reaction: CH3OH(g) <-> CO(g)+2H2(g) Calculate ΔG for this reaction at 298 K under the following conditions: PCH3OH=0.895atm PCO=0.115atm PH2=0.200atm Homework Equations ΔG=-R*T*ln(K) where R is the gas constant 8.314 J/molK, T is 298 in...
  11. K

    Free Energy calculation in Monte Carlo simulations

    Hello everyone, I am currently working on a classical MC simulation of helimagnets and I try to calculate the experimentally measured phase diagram. Up to now I am able to reproduce a large piece of the phase diagram by using a single site Metropolis update and simulated annealing...
  12. C

    Light bulb & photovoltaic cell & power transformer combo for FREE energy

    Does anyone think that it's possible to have a perpetual motion machine electricity generation of a combo of a light bulb shining light on photovoltaic cells that are connected to power increase transformer coils to power that light bulb? I suppose there would have to be some kind of way to...
  13. Z

    Why Does Heat Stop Flowing When Q=TS in Thermal Equilibrium?

    Is defined as F = U - TS and it is the energy needed to create a system minus the heat it can get for free. But why is the heat that it can get for free given by: Q = TS I know the thermodynamic relation: S = Q/T So in that way I understand it. But how do you know, that the system will be...
  14. A

    Understanding Helmholtz Free Energy: Get Heat for Free?

    I'm having some trouble understanding this concept. Why is it that you sometimes can get heat for free from the environment? Like suppose you have a system, on which you make an energyconsuming proces which creates entropy. Then you subtract TΔS because apparently heat can enter when the entropy...
  15. B

    Definition of the Gibbs free energy

    In the equation \Delta G^{\ominus} = \Delta H^{\ominus} - T\Delta S^{\ominus} does the temperature refer to the temperature of the system, or the temperature of the surroundings? BiP
  16. J

    Confused about gibbs free energy

    Wikipedia says : In thermodynamics, the Gibbs free energy (IUPAC recommended name: Gibbs energy or Gibbs function; also known as free enthalpy[1] to distinguish it from Helmholtz free energy) is a thermodynamic potential that measures the "useful" or process-initiating work obtainable from a...
  17. J

    Gibbs free energy change at constant pressure is zero?

    gibbs free energy change at constant pressure is zero?? IS gibbs free energy change at constant pressure zero? ΔS = q / T. At constant pressure q = ΔH so ΔS = ΔH / T So ΔG = ΔH - ΔH/T . T = 0 I think i am wrong but where? My friend tells me that q involved in enetropy is...
  18. C

    Relation between binding free energy and solubility

    Suppose we have a ligand binding to a receptor in solvent medium. I am interested to know whether there is any relation between "Binding free energy" and "Solubility". Extemely sorry if I posted my question in the wrong section. I'd be glad if anyone could help me out with this. Regards...
  19. W

    Perpetual machine by using free energy of magnets Possible?

    Does magnets posses free energy? Does the machine shown in image will run? If no...give reason... I know it seems to voilate 1st law of thermodaynamics...But why it voilates it?
  20. S

    Thermodynamics, Helmholtz free energy, Legendre transformation

    Homework Statement The Helmholtz free energy of a certain system is given by F(T,V) = -\frac{VT^2}{3}. Calculate the energy U(S,V) with a Legendre transformation. Homework Equations F = U - TS S = -\left(\frac{\partial F}{\partial T}\right)_V The Attempt at a Solution We...
  21. A

    Gibbs Free Energy Change of a Reaction

    So, in my thermo book, it says that the gibbs free energy change of a reaction is the free energy received by the system at constant T,p and constant chemical potential when the extent of the reaction varies by one mol. The part that is confusing me is the "constant chemical...
  22. C

    Gibbs Free Energy: Explained & Explored

    I don't think I completely understand what Gibbs energy is, Is it the work you can get out of a system at fixed Temperature and pressure. Does anyone have another angle on it cause It seems weird to me.
  23. R

    Thermodynamic equilibrium constants calculating the reaction free energy

    Can someone please help me answer this question and explain the concepts/solution step by step: Prof. W.H Bogus claims that he has prepared a powerful new catalyst that makes it possible to synthesize NH3 with a 70% yield in a reactor operating 500K and 2 atm pressure and having a feed...
  24. C

    Free Energy Thought Experiment Question

    I have a thought experiment I don't understand. Imagine there's a grain of salt that weighs 5 mg and it's 1mm above above a pool of water and it's on a very thing piece of flimsy material that takes about 1*10^-5 Newtons of force to break. Using Newton's 2nd law, I get the grain of salt is...
  25. J

    Finding Standard Gibbs Free energy for half cell reaction.

    The standard potential of the Cl−(aq.)|AgCl(s)|Ag(s) electrode in the vicinity of T = 298 K has been found to fit the expression E\theta/V = -0.00558 + 2.6967x10^-3(T/K) - 8.2299x10^-6(T/K)^2 + 5.869x10^-9(T/K)^3 Find the standard Gibbs free energy, the standard enthalpy, and the standard...
  26. G

    Free energy and Chemical Energy question

    \DeltaG = -n F Emax and \DeltaG = \DeltaG\circ + RT ln(Q) When do we use the first equation and when do we use the second one?
  27. Truecrimson

    What Is the Minimum Work to Withdraw a Magnetic Core?

    Homework Statement Please see P4, P5, and P6 in http://panda.unm.edu/pandaweb/graduate/prelims/SM_S09.pdf "...What is the minimum work that must be performed to completely withdraw the core at constant I and T?" Homework Equations The Attempt at a Solution I have no idea how to do this type...
  28. C

    How is the consumption of free energy defined and measured in thermodynamics?

    We know that free energy is a well-defined concept in thermodynamics. How about the *consumption* of free energy? Are there well-defined criteria for saying "system X has consumed E amounts of free energy" ? That requires us to define what is a physical system, and secondly, to define...
  29. N

    How does temperature affect the dissociation of acids?

    Hi everyone, There is one major concept I am struggling with, and that is why acids dissociate more at higher temperatures. How can this be explained in terms of molecular energy levels becoming accessible at higher temperature, and the fact that the spacing between adjacent energy levels id...
  30. G

    Calculating Change in Free Energy from Rod Displacement

    hi i have a question concerning free energy in the attached file you can see 3 rods. think of them as 3 parallel forces, that attract each other by a force F. the force is some arbitrary force of the form: F=a/r^6 where a is a real parameter now imagine that caused by fluctuations(e.g...
  31. C

    How Do You Calculate DeltaG for a Reaction at Non-Standard Pressures?

    Homework Statement At 699 K, DeltaG (degree)=-23.25kJ for the reaction H2(g) + I2(g) <-> 2HI(g). Calculate DeltaG for this reaction if the reagents are both supplied at 10.0 atm pressure and the product is at 1.97 pressure. Homework Equations I believe this is the relevant equation G=G(degree)...
  32. S

    Gibbs free energy partial derivative

    g = u + Pv - Ts To find the partial derivative of g with respect to T at constant P, we do the following. dg = du + vdP + Pdv - Tds - sdT and du = Tds - Pdv. Therefore, dg = vdP - sdT. At constant pressure, dg = - sdT. Therefore, the partial derivative is - s. I think we could...
  33. R

    Gibbs Free Energy, How to find G with only Hstand and Gstand

    Homework Statement For the decomposition of Ag2O(s), what is the Gibbs free energy change at 500K (assuming delta H and delta S do not vary with temparature? delta standard Gformation: -61.0 kJ/mol delta standard Hformation: -29.7 kJ/mol Homework Equations deltaG = deltaH -...
  34. Simfish

    Is Gibbs free energy ever relevant for particle physics?

    And are reactions in particle physics reversible at all? If so, why don't we ever see Gibbs free energy used in particle physics equations?
  35. Topher925

    Electrochemical cells: Is gibbs free energy dependent upon concentration?

    Is the gibbs free energy of some reaction in an electrochemical cell dependent upon reactant concentration? The Nernst equation clearly states that open circuit potential is dependent upon concentration, and basic thermodynamics states that open circuit potential is directly proportional to...
  36. P

    Connection between Free Energy and Action

    Could anyone please, explain the connection between the Free Energy and the Action? I know the definitions of each but not sure about the connection. I read somewhere that the free energy is the same as the action when calculated "on-shell". What does this "on-shell" thing mean in this...
  37. J

    Non-spontaneous reaction and Gibbs Free Energy

    Quartz, SiO2(s), does not spontaneously decompose to silicon and oxygen at 25 degrees Celsius even though the standard entropy change of the reaction is large and positive (deltaS = +182.02 J/K). Explain why. I am confused by this one fundamentally because it seems like common sense that...
  38. G

    Can someone help me understand enthelpy and free energy?

    I'm teaching myself thermodynamics and I'm having trouble understanding Helmholtz and Gibbs free energy. My understanding of enthalpy (H) is pretty solid I think. I understand that enthalpy is a state variable, meaning its change tells you how much heat (Q) is absorbed or released by a system...
  39. C

    Gibbs Free Energy Homework: Final T & P, Change in G

    Homework Statement You have two parts of a tank, divided by a divider. On the larger side, you have 4 mol of N2 gas and on the smaller side you have 1 mol O2 gas. Both gasses are are the same T and P. The divider is removed and the gasses mix. What is the final T and P? What is the...
  40. H

    Is this free energy possible ?

    hi, I'm studying a system using self-consistent mean field theory. And I have obtained its free energy, which however looks a bit unusual in that it bears a steep (almost abrupt) rise across the phase transition point (see the figure). This feature brought about fierce questioning from my...
  41. O

    Free energy or an infinite universe, which one is it?

    It seems to me we must pick on or the other when you get right down to it, at the moment theory and evidence suggests free energy is impossible but at the same time the universe supposedly popped into existence so that would also suggest free energy is possible or that the universe/something has...
  42. J

    A basic question about entropy and free energy

    I'm wondering about entropy, free energy and disorder. I see entropy defined along the lines of "the amount of energy within a system that is unavailable to be used for useful work". So, the energy that is available to do work, ie. the Free energy, is given by the internal energy minus the...
  43. K

    Thermodynamics: Gibbs free energy from this battery reaction?

    Thermodynamics: Gibbs free energy from this "battery" reaction? Homework Statement I'm reading my textbook and it gives an example. The dH of the reaction is -316kJ/mol so that much energy is released by the reaction itself. Additionally, the entropy of the products are higher than the...
  44. A

    How Do G vs T and G vs P Graphs for Water Change with Pressure and Temperature?

    Homework Statement Do a qualitative sketch of a G vs T (and G vs P) graph for water at liquid, solid and gas phases at atmospheric pressure. How would the graphs differ at a pressure of 0.001 bar/slightly higher temperatures? Homework Equations None that I can think of. The Attempt at a...
  45. O

    Thermodynamics: Gibs free energy

    Homework Statement What is the standard Gibbs free energy of formation of water vapor at 25 C, if , for the reaction shown below under standard conditions, Δ H = -484 KJ/mol and ΔS= -89 J/mol K? 2H2(g) + O2(g) >>> 2H2O(g) Homework Equations ΔG = ΔH - TΔS The Attempt at a...
  46. K

    Thermal physics (Gibbs free energy mostly)

    Homework Statement I know that Gibbs free energy: G=H-TS, and therefor \frac{dG}{dT}=-S , and that dS=C_P\frac{dT}{T} Now, I am to show that more generally, dS=C_P\frac{dT}{T}-\frac{dV}{dT}dP(1) (assuming that the difference between delta and d is mostly the same (symbolwise). The hint I...
  47. H

    About the quasi-harmonic free energy

    Hi guys, I'm recently working on the quasi-harmonic theory. I feel confused when i find the expression of vibrational free energy is deduced using the partion function of Boltzmann distribution, i.e., Z=Sigma{exp(-(1/2+n)*hw/kT)}. Since the phonon is boson, i tried to get the same free energy...
  48. A

    Is perpetual motion truly impossible?

    I found textbooks on physics (long time ago, when I was a student) where the authors said (paraphrase): "We do not assert that perpetual motion is impossible. It just hasn't been seen so far." What do the mentors and contributors say about that statement? (berkeman?)
  49. H

    Entropy, Free Energy and Equilibrium

    Homework Statement The enthalpies and Gibbs energies of formation of the metal oxide Ag2O are: deltaH0f = -31.05 KJ/mol deltaG0f = -11.20 KJ/mol Determine to what temperature must it be heated to produce O2(g) at 1.00 atm pressure? Homework Equations deltaG0f = -RTln(k) K = PO20.5The...
  50. H

    What Is the Correct Calculation for Kp at 900K in the Water Gas Shift Reaction?

    Homework Statement The water gas shift reaction used commercially to produce H2 deltaG std condtions = -28.6 KJ\mol Calculate the Kp at 900K Homework Equations G0=-RTln(k) The Attempt at a Solution -28.6x1000/(-8.314x900)= ln(k) k=e3.822...
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