Gibbs free energy Definition and 124 Threads

What is the difference between 1) ΔG°' and ΔG° and 2) ΔG°' and ΔG ? ΔG° I think it is the gibbs free energy at standard state means at room temperature 1 atm pressure.

Hello everyone, I'm reading some basics of chemistry thermodynamics, and it's hard for me to figure out what is the actual meaning of free energy. could someone please help clarifying this giving specify, real life examples, like applications in mechanical engineering. Thanks

ΔG=ΔH-TΔSsystem and ΔSsystem=qp/T and isn't qp=ΔH? Which means ΔG=0 always which is obviously wrong. But the derivation for Gibbs Free Energy is based on qsurrounding=-qsystem so shouldn't the term be equals to 0?

ΔG=ΔG°+RTlnQ are for reactions that are not under standard conditions. What does it mean under non-standard conditions for the ΔG? And what is the Q in this case? Is it Qp where it is based on the partial pressure of the gas or Qc which is based on the concentration? Thanks

The decomposition potential is always higher than the theoretically determined potential by thermodynamics. E=η+Eeq where E is the decomposition potential, η is the overpotential and Eeq is the theoretically determined potential. And ΔG=-nFE and if we were to substitute the decomposition...

The decomposition potential is always higher than the theoretically determined potential by thermodynamics. E=η+Eeq where E is the decomposition potential, η is the overpotential and Eeq is the theoretically determined potential. However since the decomposition potential is higher doesn't it...

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, ΔH = -484 kJ/mol and ΔS=-89 J/mol K? 2H2 + Os→2H2O Homework Equations ΔG = ΔH-TΔS The Attempt at a Solution Usually I can do these problems...

I posted this earlier, but I just realized it might have been in the wrong section. Sorry Okay, so consider you have system in which ΔG<0 and ΔS>0. Using Gibbs free energy (ΔG=ΔH-TΔS), you'll know that it will always be negative. As the temperature increases, it will actually become more and...

Homework Statement Can anyone explain to me the gibbs free energy curve? Homework EquationsThe Attempt at a Solution [/B] What is the domain of the curve and how should I interpret it?Thanks.

When reading some material concerning Ginzburg-Landau theory of superconductors, I got the following sentence: The appropriate thermodynamic potential for describing a superconductor in an applied magnetic field is the Gibbs free energy ##G## (natural variable ##H##) and not the Helmholtz free...

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)...

When you get the equation for the Gibbs free energy, why do you multiply -T? Can't you multiply just T? I thought about this and came up with an answer of my own, which goes like 'Because its Gibbs 'Free' Energy, when you have that free energy ( \Delta G >0) you have the energy to do...

Homework Statement For a certain reaction, ΔG = 13580 + 16.1 T log10(T) - 72.59 T. Find ΔS and ΔH for the reaction at 298.15 K. Homework Equations ΔG = ΔH - TΔS \left[\frac{\partial (\Delta G)}{\partial T} \right]_P = - \Delta S The Attempt at a Solution For the sake of this thread's length I...

I know that gibbs free energy for say a body will be equal to = Gibbs free standard energy at 1M and Ph7(-rtlnkeq) (Where k is the concentration of product/ concentration of reactant at equilibrium)+rtlnk. How can we use the standard gibbs free for irreversible spontaneous processes? Is it...

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

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...

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...

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

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?

*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...

***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...

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...

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...

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...

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...

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)...

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...

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...

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...

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?

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...

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.

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

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...

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...

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...

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...

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...

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...

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...

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...

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

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...

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...

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...

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.

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...

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...

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 -...