What is Free energy: Definition and 302 Discussions

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. Q

    Van der Waals gas - free energy

    For this problem, I'm really jst trying to figure out everything that is going on and then I can simply follow through with the derivatives once I know what I'm working with. Q: For the van der Waals gas, introduce the free energy as F = U – TS and verify that its derivatives over V and T...
  2. Z

    Understanding the Helmholtz free energy, what does 'useful work' really mean?

    When it comes to thermal/statistical mechanics, I'm a little retarded... so bear with me please. I've used the helmholtz free energy (F) dozens of times, almost as many times as I've heard and read that F is a measure of the 'useful work attainable from a closed thermodynamic system,' at...
  3. M

    Ok so what if someone does come up with free energy what then?

    How will the world have to change when we finally get an energy sorce better then anything we currently can think of? Let's suppose this energy sorc allows for deadlyer devices then nukes how do we cope with that? Do we even want to dare to create it if it's possible? Would we just end up...
  4. J

    Change in Free Energy in terms of First Law

    I understand why dE=TdS-PdV ...[1] at constant temperature and pressure Also, I see that F=E-TS and therefore dF=dE-SdT-TdS ...[2] and how combining [2] and [3] gives dF=-SdT -PdV QUESTION: shouldn't [1] be expressed as dE=TdS+SdT-PdV i.e if you're going to substitute...
  5. L

    Solubility and Gibbs free energy Qs

    Homework Statement There are a problems I wasn't sure about on my test. Trying to get answers for ones I had to guess on. 1. What is the maximum [Mg] that can be achieved in an aqueous solution of Mg(OH)2 with a pH=12.50? Ksp (Mg(OH)2)=5.6e-12 2. Determine the max solubility of CaF2...
  6. A

    Thermodynamics - Gibbs Free Energy Question

    Homework Statement I'm having some difficulty with this question, not exactly sure how to start it. Any suggestion would help. Thanks At 2.02 atm water boils at 121 °C. Calculate the change in the Gibbs free energy when one mole of steam at 121 °C and one atm condenses to liquid water at...
  7. G

    Gibbs Free Energy: Unlocking Available Work Potential

    the total amount of energy able to do work is the gibbs free energy of a reaction. dG=dH-TdS according to this equation, the higher the entropy gain of a system(dS) in a reaction, the more work the system can achieve. I'm confused here. I thought entropy was the energy unable to do work?
  8. T

    How much free energy have we got?

    Hey all. Our heating equipment draws air through it at 5000m^3 per hour. Lets say it's 20degC outside. The fan pulls the air through and the exhaust air is 6deg cooler. So we have scavenged that 6degC for our use. Excellent. So let's pretend there are not any system...
  9. D

    Entropy, free energy and chemical potential of mixtures

    Hi, Homework Statement Consider a mixture of different gases with N_i molecules each (i=1...k denotes the species). For ideal gases the following relation yields: S(T,V,N_1,...N_k)=\sum_{i=1}^k S_i(T,V,N_i) a)Give explicit expressions for the entropy, the internal energy, Helmholtz free...
  10. L

    Gibbs Free Energy: Queries & Answers

    Hi, I've recently started studying chemistry and have being going over gibbs free energy.. I understand it is a driving force causing chemical and physical changes but during my course of reading I did have some queries stem to mind. 1) In relation to equilibrium why is it that a reaction...
  11. R

    Standard heats of formation (enthelphy, free energy)

    Quick question: why are the standard heats of formation 0 for pure elements?
  12. C

    Enthelpy and it's use in Gibb's Free Energy

    Lately I've been struggling with the idea of enthalpy and what it means conceptually, especially in its use in Gibb's free energy. There is nothing in the definition of change in enthalpy that would connect logically to spontaneity or free energy. After thinking about it for a couple days...
  13. S

    X: Free Energy - Get Help and Ideas Here!

    Hi to all! I'm new in this forum and i would like to share some thoughts with you guys! i'm 40 years old and I'm thinking on create a motor with magnetic materials which will provide me electricity for my house! i need some help with what materrials i have to buy and what dimensions i...
  14. S

    Cat's Free Energy Project - Discussions & Tips

    Hi to all! I'm new in this forum and i would like to share some thoughts with you guys! i'm 40 years old and I'm thinking on create a motor with magnetic materials which will provide me electricity for my house! i need some help with what materrials i have to buy and what dimensions i...
  15. Q

    Exploring the Meaning of Helmholtz & Gibb Free Energy

    Hi guys, We all know that Helmholtz free energy, Gibbs free energy and Enthalpy are defined by Legendre transformation. For Enthalpy H=E+PV, I can understand it as the energy required to "displace the atmosphere" plus "creating the internal energy of system". What about Gibb free energy...
  16. L

    Helmholtz Free Energy: Finding C_H-C_M Relation

    Homework Statement The Helmholtz free energy is written as: dA=-SdT-pdV-VMdH when an incompressible liquid is placed in a magnetic field H. Thus, the free energy can be written as since -pdV=0: dA=-SdT-VMdH The two heat capacities can be defined as: C_H = T (dS/dT)_H and C_M = T...
  17. I_am_learning

    Is free energy Really Possible?

    I have seen lots of Ads over the internet that promise to generate electricity from nowhere by utilizing Earth's magnetic fields or other arrangements. Some promise to increase the efficiency of household electricity use by placing their equipment in series with the main supply. Are they...
  18. A

    Can Bedini Free Energy Motors Really Defy the Laws of Physics?

    Is it true? Does this really defies a law of physics? (More output than input). or is it bluff...
  19. X

    Free energy from Thorium to Radon

    228 224 4 Th --> Ra + He 90 88 2228,031015u --> 224,020186u + 4,0026033u 228,031015u - [224,020186u + 4,0026033u]= 0,0082257u 0,0082257u x 931.49 MeV = 7662157,293eV 7662157,293eV x...
  20. C

    Minimising helmholtz free energy

    Homework Statement Show that the most probable energy minimises the Helmholtz free energy. Homework Equations F=E-TS(E) where S(E) is the entropy of te system of given energy E. The Attempt at a Solution Not sure how you would 'show' is ? P(E) = 1/Z *weight funciton*exp(-beta E)
  21. M

    Understanding Entropy and Free Energy in Chemical Reactions

    I'm having trouble understanding why in a reaction, when the free energy G of the product equal the free energy G of the reactant, the reaction is at equilibrium. Here, as my book say, the system has reached its minimum free energy. I don't really get why... Could someone explain to me...? Thanks!
  22. N

    A sort of free energy? Possbilble or not

    A sort of free energy? Possbilble or not Hi there, Let me start off by saying that I am a College student at Penn College of Technology in Williamsport, PA and I am studying Tool making Technology and Automated Manufacturing, I'd like to refer to myself as THINKER. I've been creating my own...
  23. M

    Pressure equilibrium/Gibbs free energy question

    Hey everyone. First let me say thanks for reading this. I am doing some practice exams to prepare for a Chemistry exam on Thursday, but I’m finding I don’t know the material very well. The problem I am having the most difficulty with right now has two parts, one relating to pressure...
  24. P

    How Does Temperature and Pressure Affect Gibbs Free Energy in Water?

    Homework Statement Suppose you have a mole of water at 198 K. and atmospheric pressure. use the data at the bac of this book to determine what happens to its gibbs free energy if you raise the temperature to 303 Kelvins. To compensate for this change, you could increase the pressure of the...
  25. S

    Solve for \Delta G at 1000K: NH_{4}Cl Reaction

    Homework Statement The reaction is NH_{4}Cl(s)\rightarrow NH_{3}(g)+HCl(g) \Delta H^{o}=+176 kJ and \Delta G^{o}=+91.2 kJ at 298 K What is the value of \Delta G at 1000 K? Homework Equations \Delta G=\Delta H-T\Delta S The same applies if all 'deltas' are standard The Attempt at...
  26. E

    Calculating free energy from Ksp

    Okay so I'm confused. In my book it says that ksp for Ca(OH)2 = 6.5E-6 and \Delta G=-898.5 yet when I use the equation \Delta G=-RTln(Ksp) the value I get is 29.59KJ/mol. I used R=8.314 and T=298K. What's up with that? Thanks.
  27. F

    Is Free Energy a Viable Source of Power for the Future?

    I have this strange feeling, the solution is almost ready, I believe we are already entering the age of Free Energy. But no, it won't happen overnight. If I may ask, what source of energy exists anywhere in the world? Constant and is always available, completely safe and doesn't emit harmful...
  28. Ahmed Abdullah

    What is the relationship between temperature and Gibbs free energy?

    \Delta G = \Delta H - T \Delta S I don't understand this equation satisfactorily. I have learned so far that endothermic reaction having a positive \Delta S_{system} is spontaneous at higher temperature because T\Delta S out-compete the enthalpy term and make the free energy change...
  29. S

    Activation free energy for nucleation

    Hi everyone, Question In metals, for homogeneous nucleation, activation free energy required for the formation of a stable nucleus are different when the nucleus are considered as a cube and considered as a sphere and the relation between them is energy for cube is almost double of the...
  30. N

    Thermodynamics: Helmholtz free energy

    Homework Statement Hi all. Lets take a look at the Helmholtz free energy. It is defined as the amount of energy one has to put into create a system once the spontaneous energy transfer to the system from the environment is accounted for. Now let's look at it once we have created the...
  31. J

    Spontaneity of reactions and free energy

    Does anyone know of a clean proof that a reaction will occur at constant temperature if the change in Helmholtz free energy is negative, or at constant temperature and pressure if the change in Gibbs free energy is negative? The only `proofs' I've found rely on the fact that the entropy...
  32. A

    Free energy of solids & Einstein crystal

    Dear all, I'm coding the calculation of the free energy of an SiO2 crystal structure Using a 2-body Buckingham potential. I'm attempting to use the method of Frenkel and Ladd which consist in transform your solid reversibly into an Einstein crystal. I've read the excellent book...
  33. C

    The ever elusive free energy device

    The ever elusive "free energy" device... Hello. Let me begin by stating that I have no formal physics/science training, and am not here to wear a tin foil hat, close my eyes and claim that I've solved the worlds problems. That being said... I have a theory, and I'd like to be told why it...
  34. N

    Free energy of a rotational system.

    If one has a diatomic molecule with energy levels \epsilon_l = \frac{h^2 l(l+1)}{2I} l = 0,1,2,3,4,5... if the degneracy is given by g_l = (2l+1) How does one show that the Helmholtz free energy at low temperature (h^2/Ikt large) is given by F = -3kT e^{-h^2 / IkT} + ...
  35. N

    Reason behind the definition of Helmholtz free Energy

    What is the reasoning behind defining the helmholtz free energy as F = -kT ln Z? I always wanted to know why it was just defined as the above. Is it as a form of convenience because the macroscopic theromodynamic observables of a system at constant temperature (ie the canonical ensemble) are...
  36. O

    Understanding the Relationship between Exergy and Gibbs Free Energy

    Are the concepts of exergy and Gibbs Free Energy related? What are the differences between them? Thanks in advance for any help.
  37. C

    Unravelling the Mystery of Free Energy

    free energy?? water disasotiates to H+ and 0H- if you could take the dissasociated ions away, and combine them how much energy could you get out? In the liquid remaining, more would dissosciate, and the process could be continued. Where does this energy come from - it sounds like free...
  38. K

    Unfolded to Folded: Exploring the Entropic Free Energy Barrier

    I have a question about protein folding. I have heard that there is a free energy barrier to overcome in going from the unfolded (ensemble) to folded states, and that this barrier is largely entropic -- i.e., as the (idealized, general) protein starts to fold, it loses more in entropy than it...
  39. W

    Helmholtz free energy decreases

    Helmholtz free energy decreases... Hello... I'm having trouble getting my head around something. I'm not exactly sure what is meant by the Helmholtz free energy (F) decreasing in a system that's in thermal equilibrium with it's environment. Under what circumstances does it decrease...
  40. F

    How Do You Calculate the Equilibrium Constant from Free Energy of Formation?

    [SOLVED] free energy of formation Homework Statement Consider the reaction 2NH3(g) --> N2(g) + 3H2(g) If the standard molar free energy of formation of NH3(g) at 298 K is –16.45 kJ·mol–1, calculate the equilibrium constant for this reaction at 298 K. The correct answer is 1.71E-6...
  41. N

    Statistical mechanics - Helmholtz free energy and Z

    Homework Statement The neutnral carbon atom has a 9-fold degeerate ground level and a 5-fold degenerate excited level at an energy 0.82 eV above the ground level. Spectroscopic measurements of a certain star show that 10% of the neutral carbon atoms are in the excited level, and that the...
  42. J

    Gibbs Free Energy Homework: CaCO3 <-> CaO + CO2

    Homework Statement CaCO3 <-> CaO + CO2 At 900K, equilibrium pressure of CO2 is 0.0423 atm. Calculate Gibbs Free energy of Reaction and K.Homework Equations delta G = -RTlnKThe Attempt at a Solution delta G = 5656.3 cal/mol K = 0.0423 I have a feeling that this is incorrect Could someone...
  43. S

    Where to find the surface free energy value?

    Hello, I am working on some calculations and need to find the surface free energy value of amorphous SiO2 and MgO. will anyone please tell me where I can find those values? Thanks a lot
  44. C

    Thane Heins and his free energy machine

    Thought you guys might find this article interesting and that maybe it would spark some conversation. What are your thoughts on this? I think it's pretty incredible, but there has to be something that limits the process so that he can't take power away from the motor completely. Video...
  45. L

    Free Energy Diagrams: Understand Endo/Exothermic Reactions

    It's thermo.. so I just posted it in the physics forums but.. a free energy diagram is supposed to represent G right? We normally conclude whether a rxn is endo/exothermic depending on whether the product is at a "lower" or higher energy than the reactants just by looking at the diagram...
  46. J

    Atp synthase and gibbs free energy

    Hi, I'm trying to answer a question that I'm stuck on. The question is as follows: -------------------------------------------------------------- If the Gibbs free energy change (deltaG) for ATP hydrolysis in a cell is -57 kJ/mol and the free energy change for transporting a proton from...
  47. J

    Will a superconducting dynamo in space produce free energy?

    I have read in several places that superconducting materials are the closest phenomenon to perpetual motion known to science (constant flowing electrons within a circuit without resistance). The problem is that the energy required to cool the inducting material to its superconducting temperature...
  48. S

    Why Do We Square Molarities in Free Energy Calculations for HCl Dilution?

    Calculate ΔG for the dilution of aqueous HCl from 0.89 M to 0.253 M at 25°C. THis was a question I had to do some time earlier for one of my assignments. I got some help from a classmate and he said THE FOLLOWING: "H+ and Cl- are equimolar so you have to put them to the power of two...
  49. S

    What is the ΔG for the dilution of aqueous HCl from 0.89 M to 0.253 M at 25°C?

    2NH3(g) + 3O2(g) + 2CH4(g) http://a1.educog.com/res/sfu/batchelo/Gallery/thermodynamics/Tcat.rxn.arrow.gif 2HCN(g) + 6H2O(g) ΔH° for this equation -939.8 kJ ΔS° for this equation 165 J/K ΔG° at 232°C, for this equation -1023.1 kJ Are the following statements about this process...
  50. M

    Calculate Free Energy for Formation

    I realize that this is a chem prob, but I'm stuck with what I thought was a straightforward problem while studying for my physical chemistry exam. Homework Statement The standard molar enthalpy of combustion of solid phenol (C6H5OH) is -3054 kJ/mol at 298k and it's standard molar entropy...
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