# Questions tagged [free-energy]

Also known as Gibbs energy, it is the enthalpy minus the product of thermodynamic temperature and entropy.

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### How come ΔG∘ is related to the equilibrium constant?

As I understand it, standard state is when the pressure of a gas is 1 bar and quantity 1 mol. Now the following relation holds: $$\Delta G^\circ=-RT \ln(K)$$ Suppose I declare a new standard state to ...
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### Gibbs Free Energy, Temperature and Equilibrium [duplicate]

I was recently taught one of the Gibbs Free Energy formulas, where the change in Gibbs Free Energy is related to the change in enthalpy and entropy ∆G = ∆H - T∆S, and that the system is at equilibrium ...
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### If the electron affinity for a neutral element is positive (i.e. endothermic process), is the anion more stable than the neutral atom (at STP)?

This might be a bad question, but I have to ask because I'm finding conflicting answers online. Let's say that I have the following reaction: $$O + e^-\rightarrow O^-$$ While I understand that the ...
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### Change in Gibbs energy for lithium redox reaction

I was reading an electrochemistry book by Thomas F. Fuller, in this book the thermodynamic values for the lithium redox reaction at standard conditions are the following: Reaction $\Delta G^o$ [kJ/...
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### Gibbs energy of an imperfect crystal

Our materials professor likes to do Kahoot quizzes and I am confused about why the following statement is true: A defect in a crystal gives it higher energy. I know that an imperfect crystal has a ...
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### Calculation of Reaction Extent as a Function of Pressure and Temperature: Issue with Activity-Based Approach

I'm working on modeling reactions involving combinations of hydrogen (H), nitrogen (N), and strontium (Sr) elements. I've obtained the temperature-dependent Gibbs free energy of formation, enthalpy, ...
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### Confused about free energy equation and entropy change

I'm confused about two equations and how they relate to each other. These are $\Delta S = \Delta Q/T$ and $\Delta G = \Delta H - T\Delta S$. To derive the Gibbs' free energy change for the universe ...
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### How does cell potential change with temperature for positive enthalpy and negative entropy?

A recent United States National Chemistry Olympiad question asked: A certain voltaic cell has a standard cell potential that increases with increasing temperature. Which best explains this ...
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### Define a rate-determining step and an energy barrier for a multi-step reaction profile

I am currently making reaction profile by means of DFT calculations. I am able to correctly draw a whole reaction profile. However, I am struggling to find what exactly is the energy barrier of a ...
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### Change in entropy with micelle formation

Micelles are formed only above the Kraft temperature. We know ∆G = ∆H - T∆S (Gibbs energy relation). For micelle formation to be spontaneous, ∆G has to be negative. This implies ∆H - T∆S has to be ...
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### Inconsistency in between Nernst Equation and Gibbs Free Energy Equation [closed]

Part 1 - Derivation of the Gibbs Free Energy Equation: [copied from this] Using the fundamental equations for the state function (and its natural variables): \begin{align} \mathrm{d}G &= -S\...
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### Spontaneity of irreversible reactions

I saw this reaction in my textbook: $\ce{NH4Cl(s) -> NH3(g) + HCl(g)}$ given $\Delta{H}_{r} = \pu{176 kJ/mol}$ and $\Delta{S} = \pu{0.285 kJ/(mol \cdot K)}$ On a worksheet my teacher gave me, I saw ...
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### What is the difference between standard Gibbs energy and Gibbs energy of formation?

Good day guys, I am reading a book on electrochemical engineering, I came across some definitions of Gibbs energy and I am a bit confused as the book does not go into a lot of detail. The book first ...
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### Justifying that Standard Entropy of a Reaction is a Constant of Temperature

One of the parts in a question I'm trying to solve for an assignment goes like this: A key issue in the Hydrogen Economy is Hydrogen Storage. This can be restored if a substance $X$ can bind to $H_2$....
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### Why 40J energy was wasted in case of a non spontaneous process by the system? [closed]

If there is a system which while undergoing a process produced 30J energy and wasted 40J energy therefore the useful energy was -10J and this explains the process was non spontaneous because ∆G is ...
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### Does it make any sense to graph 1/T versus ln(Kc)?

I calculated $K_c$ experimentally for the reaction $$\ce{CO2 + H2O -> H2CO3}$$ at different temperatures. Because $\Delta G =-RT\ln(K)$, I thought that graphing 1/T against $\ln(K_c)$ would give me ...
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### ∆G or ∆G° to predict spontaneity

I have a doubt about using Gibbs free energy to predict the spontaneity of a reaction. It is shown that ∆G = ∆G° + RT ln (Q). That said, in order to predict which direction the reaction spontaneously ...
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### Gibbs Free Energy - Maximum Work

I've been having a lot of trouble trying to truly understand Gibbs free energy from a practical perspective. I have no background in physical chemistry, but I think I have a firm grasp on many of the ...
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### Is there an algebraic form for the textbook reaction coordinate curves?

So here is a curve often used in textbooks to illustrate a reaction coordinate. It's a nice short-hand device to learn the relationship between kinetic and thermodynamic parameters that control the ...
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### Interpretation of Helmholtz energy and Gibbs energy

I know that this question has many other variations on this site, but I'm trying to see if I understood Helmholtz and Gibbs energy properly or not. The material I'm reading from is Physical chemistry ...
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### Why does the reaction of dissolution stop at an equilibrium point? [closed]

The formula for Gibbs free energy is $\Delta G=\Delta H-T\Delta S$. If Gibbs free energy is negative, the reaction is spontaneous. This also applies to dissolution reactions. However, we know that ...
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### Is the maximum work done by voltaic cell per mole of reaction? [duplicate]

From the equation $w_{elec,rev}=-nF\Delta E$, and n = the number of moles of electrons transferred in the overall redox reaction, does that make the work per mole of the redox reaction? I am confused ...
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### Why can one set the Gibbs free energy change to 0 when calculating the standard free energy change?

I am trying to understand the following equation: $$\Delta G = \Delta G^{\circ} + RT \ln\left(\frac{[C][D]}{[A][B]}\right)$$ for a reversible reaction with reactants A and B and products C and D. The ...
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### Gibbs energy of electron transfer

The reaction Gibbs free energy of a cell is $\Delta_\mathrm{r}G^\circ = -nFE^\circ, \tag{1}$ and the Gibbs energy of photoinduced electron transfer according to IUPAC is \Delta_\mathrm{ET}G^\circ = ...
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### True or false: "If a reaction has a large negative value of ∆G, then it will be a fast reaction."

I recently took a Gen. Chem. 2 exam that contained this question. I answered false, as I knew that thermodynamics and kinetics are separate matters. My professor said the answer is true. I pressed him ...
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### Loss of entropy and solvation energy in proteins

I am reading a chapter on protein stability. One section outlines the role of salt bridges or ion pairs in the stability of a protein. The excerpt goes as follows (italization added for emphasis): ...
The formulas I can use are $\Delta$G = H - T$\Delta$S, and $\Delta$G = $\Delta$G(s.t.d) + RTlnK I understand that when Kc is 1, the reaction is barely spontaneous and thus I can use the first formula ...
I want to know if it is possible to derive heat capacities, in this case, in constant volume from another thermodynamic Potential which is not the Helmholtz free energy $F$. I am aware of the ...