Free energy Definition and 277 Threads

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...

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?

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 ==...

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...

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...

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...

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)...

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)...

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...

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...

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?

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...

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...

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.

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?

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

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...