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

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Nature of Thermodynamic Stability of CO2

In a discussion with one of my professors I was talking about carbon dioxide, during the discussion it was discussed that ${CO_2}$ is a stable compound thermodynamically. Looking up the $\Delta$G ...
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26 views

How can change in gibbs free energy be greater than enthalpy?

There is a problem in the textbook I'm studying Chemistry from that although was easy to compute, the result surprised me conceptually: The standard enthalpy for a reaction is said to be: -115kJ, we ...
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Which is a better way to calculate E-cell [duplicate]

Suppose we have these two half cell reactions. In order to calculate E(Cu_+1/Cu), what is a viable way to do it. I looked up resources on when to simply reverse one equation and add/subtract the ...
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What is the difference between ΔG and ΔrG?

Consider the reaction $$\ce{A -> B}$$ The reaction Gibbs free energy, $\Delta_\mathrm{r} G$ is given by the following equation $$\Delta_\mathrm{r} G = \Delta_\mathrm{r} G^\circ + RT \ln Q$$ Now ...
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58 views

How to find deltaG when given the equilibrium constant and temperature?

For the reaction, $$\ce{N2O4(g) <=> 2NO2(g)}$$ the equilibrium constant in terms of concentration, $K_c$, at $100~^\circ\rm C$ is $0.36$. What is ${\rm\Delta} G$? I used the equation ...
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Gibbs Free energy Process v/s Reaction

How is Gibbs free energy for a reaction different from that in a process? Is it because a reaction generally occurs at a constant temperature and pressure, and so dG = dH - TdS, while for a process ...
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80 views

How can a nonspontaneous reaction occur?

$$\frac{-\Delta G}{T}=\Delta S_{universe}$$ (This equation applies under isobaric and isothermal conditions.) I understand that if $\Delta G$ is positive, the reaction is nonspontaneous, and adding ...
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Difference between bulk free energy and cohesive enrgy

I am writing a lammp's code to calculate size dependent surface energy of FCC copper nano particles. First of all I need to calculate total bulk energy of each atom in the crystal. my question is that ...
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50 views

Is water committed to vapor state at boiling point or after? [duplicate]

Quite early into my studies, I learnt about phase changes with this graph. I’m just going to focus on vaporization/condensation. I learnt that the plateau was caused because all the heat was going ...
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116 views

How to treat pressure in computational chemistry?

I have a reaction where a gas at high pressure and a solution with all kinds of species is involved. How do I take pressure correctly into account to get reasonable values for $G$? Do I calculate ...
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22 views

How do you find the heat capacity of a calorimeter?

My instructor gave me the formula: $$C_\mathrm{cal} = \frac{C_\mathrm{bomb}}{\text{steel}+C_\mathrm{water}}$$ I know that the heat capacity for water is $4.184~\mathrm{J\,g^{-1}\,^\circ C^{-1}}$ and I ...
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41 views

Gibbs Free Enegy using electrode potential under standard conditions

I have a question regarding the number of moles when using the equation $$\Delta G=-nF\Delta E$$ I understand that n is the number of moles transferred in the overall redox reaction, however, it ...
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reconciling free energy equations

I am struggling with a very basic concept and I think the issue lies in the definition of standard states. When calculating standard state free energy change via Gibbs equation $$\Delta G^ \circ = ...
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51 views

Gibbs Free Energy and Entropy

I understand Enthalpy, the exchange of energy between products and reactants. But what is Gibbs Free Energy and Entropy? I know that Gibbs free Energy is the difference between the change in Enthalpy ...
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25 views

Energy required to break salt bridges in peptides and proteins

Is there a way to calculate the energy required to break a salt bridge in a peptide or on the exposed surface of a protein in aqueous solution? Is there any useful literature on this topic? I'm ...
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1answer
62 views

Chemical potential and it's implications in an open system

Take the fundamental equation for the Gibbs free energy of a system: $$dG=VdP-SdT+\sum_i\mu_idn_i$$ Thus, the chemical potential can be defined in terms of the Gibbs free energy as follows: ...
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66 views

Utility of Delta G

What is the main utility of delta G? As far as I could understand, if we do not know whether the reaction we are dealing with occurs in nature or not, we would not be able to tell in which direction ...
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122 views

Why are Kc and Kp interchangeable in the free energy-equilibrium equation? [duplicate]

In this equation that relates Standard free energy and the equilibrium constant: $\Delta Gº=-RT \ln K_{eq}$ My textbook (and my teacher) say both $K_p$ (constant related to pressure) and $K_c$ ...
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Active mass,Pressure and concentration

The concentration is connected to the activity via $$a(\ce{A})= \gamma_{c,\ce{A}}\cdot{}\frac{c(\ce{A})}{c^\circ},$$ where the standard concentration is $c^\circ = 1\:\mathrm{mol/L}$. At reasonable ...
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52 views

Which step below is rate determining

What is the rate determining step in the following energy profile? To clarify, the reaction is: A -> B -> C The energy of A is greater than B which in turn is also greater than C. The intermediate ...
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231 views

Is there a way to experimentally measure entropy?

I've been doing thermodynamic chemistry, and recently focusing on Gibbs Free Energy. Whilst doing calculations using, $$\Delta G = \Delta H - T \Delta S$$ I have been given a table of values for ...
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705 views

What is the real difference between ∆G and ∆G°?

In Brady's Molecular Nature of Matter, I read that $\Delta_\mathrm{r} G^{\circ}$ is $\Delta_\mathrm{r} G$ at $25~^\circ\mathrm{C}$. But later, it gives a value for $\Delta_\mathrm{r} G^\circ$ at ...
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When is a reaction reversible?

When speaking in thermodynamic terms, when is a reaction reversible? My attempt: A reaction is reversible when $\Delta\text{S} < 0$, because according to the second law of thermodynamics, "in ...
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89 views

Change in Gibbs free energy of vaporization reaction

In my chemistry book, I see the equation $$\Delta G_{rxn} = \Delta G_{rxn}^0 + RT \ln(Q)$$ where $\Delta G_{rxn}^0$ is the change in Gibbs free energy under standard conditions (1 atm pressure in ...
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501 views

Does Gibbs free energy of formation always equal zero for elements in standard state?

I was looking through the appendix in my chemistry textbook when I noticed that every compound that had a $\Delta H_f$ of zero also had a $\Delta G_f$ of zero. So of course the compounds that have a ...
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Is conductivity related to cell potential?

I'm currently researching some background chemistry for a school project, in which I'm investigating the effects of temperature and concentration on conductivity. My teachers suggested adding in ...
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Gibbs free energy in chemical reaction

I know this kind of question has been asked many times but I think this is a bit different. We have $G = H - TS$. Here I am talking about chemical reactions at constant pressure and temperature. We ...
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111 views

Which equilibrium constant is appropriate to use?

I have learnt that the standard free energy change is related to the equilibrium constant of a reaction by, $$\Delta G^\circ = -RT \ln K$$ Here, does $K$ refer to $K_p$ or $K_c$? Also, please give ...
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Predicting the spontaneity of non-isothermal reactions

We use free energy equations -- Helmholtz or Gibbs -- to predict whether or not a reaction is spontaneous. These equations depend on constant temperature. This forum post describes a scenario where ...
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Difference between chemical potential and gibbs free energy

I know that the chemical potential is the molar Gibbs free energy and that it is an intensive variable and that the gibbs free energy is extensive. However, they have identical units: ...
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What's the difference between ΔG° and ΔG°'

In biochemistry contexts, one often sees $\Delta G^{\circ\prime}$ ("delta G naught prime"), rather than the normal standard free energy change $\Delta G^{\circ}$ ("delta G naught"). What's the ...
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Is the Gibbs standard free energy always constant?

I am a biochemistry student and we are learning about thermodynamics. Is the Gibbs standard free energy for a reaction always constant? The equation below suggests that it changes with temperature: ...
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How are partial molar Gibbs excess functions correctly defined?

I think I've found a mistake in my thermodynamics textbook, Chemical Thermodynamics for Process Simulation, but as thermodynamics is hard and I'm a relative novice, I wanted to check here. The ...
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Why does equilibrium exist?

I've read an article that equilibrium exists when $G$ (Gibbs free energy) becomes minimum. If formation of products decreases Gibbs free energy, why won't the reaction proceed to completion so that ...
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How is change in entropy of universe related to the energy released by system that can be used to do work?

What does change in entropy ($\Delta S$) represent ? How does change in entropy of a universe ($\Delta S_{univ}$) give us information about energy available to do work. I would like to know the ...
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179 views

Pourbaix diagram – writing reactions

How would you go about writing the reaction between water and chromium metal under standard acid and base conditions? I know you would have to look at the vertical lines at pH 0 and 14 but I don’t ...
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How to find the standard enthalpy and entropy for the dissolution of silver chloride?

A maximum of $1.89~\mathrm{mg}$ of $\ce{AgCl}$ will dissolve in $1.00~\mathrm{L}$ of solution at $25.00~^\circ\mathrm{C}$. A maximum of $5.26~\mathrm{mg}$ of $\ce{AgCl}$ will dissolve in ...
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What is omega and nu in this expression?

In the picture below a proportionality equation is shown: $$\omega \propto \nu \exp\left(\frac{-\Delta G_m}{RT}\right)\propto \dots$$ While $\Delta G_m$ is the Gibbs free energy, $R$ is the gas ...
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Why is the melting of ice a spontaneous reaction?

So here's my question: we know that melting of ice is an spontaneous reaction but is it spontaneous? We have to supply energy in the form heat for the reaction to take place.
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How to determine the value for n in the Gibbs free energy and redox potential equation?

I am having a problem with this equation for redox potentials $$\Delta G=-nF\Delta E$$ In this equation I never am totally sure about what the value of $n$ should be, for example for the reaction ...
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64 views

What is the precise definition of W$_{max}$ in the context of electrochemistry and thermodynamics?

I'd like clarification of the meaning of $W_\mathrm{max}$ in the following equations (and thus in the combined result in the third equation): \begin{align} W_\mathrm{max} &= \Delta G\\ ...
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2answers
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What is the difference between ΔG and ΔG “with an o on top”? [duplicate]

What is the difference between $\Delta G$ and $\Delta G^\circ$? I couldn't figure it out. Ex: $\Delta G^\circ = -RT\ln K$ $\Delta G = \Delta G^\circ + RT \ln Q$ What is the difference, is it that ...
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Truly Understanding the Second Law of Thermodynamics and Entropy

There are some seemingly contradictory things I’d like cleared up: Second Law states: $\mathrm dS_\text{univ} = \mathrm dS_\text{sys} + \mathrm dS_\text{surr}$, and $\mathrm dS_\text{univ}$ is always ...
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Why does water evaporate spontaneously at room temperature despite dG > 0?

Standard Gibbs free energy of formation of liquid water at 298 K is −237.17 kJ/mol and that of water vapour is −228.57 kJ/mol. Therefore, $$\ce{H2O(l)->H2O(g)}~~\Delta G=8.43~\mathrm{kJ/mol}$$ ...
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286 views

Spontaneous Reaction and Gibbs Free Energy

I know how to derive the expression for the equilibrium constant starting from $dG=0$, $$\ln(K)=-\frac{\Delta G ^o}{RT}$$ However, if we are not at equilibrium, $dG$ is not necessarily zero. In this ...
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If Gibbs energy of activation is positive, how is the change to the transition state possible?

The Gibbs energy increases from the reactants to the transition state, but according to the Second Law of Thermodynamics, entropy of the universe can only increase. Why is the transition state ...
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What is non-expansion work?

I learnt that Gibbs free energy is the maximum amount of non-expansion work. But the phrase non expansion work confuses me. Work is defined as pressure times change in volume. If there is no ...
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Heat Capacity temperature dependence and Gibbs energy

I got this problem in school as a tool to get ready for International Chemistry Olympiad, but I have some problems with this challenge. So, the problem is to calculate as precise as possible the Gibbs ...
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446 views

Relative energies between reactants and products

I've been asked to draw a relative energy sketch of the reactants and the two products. The reaction being examined was adding copper acetate monohydrate to glycine in two different fashions to create ...
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347 views

Are all naturally occuring reactions exothermic?

If a reaction is endothermic, then the reaction must take energy from the environment to occur (as far as I know), and if this is the case, then to me the reaction seems energetically unfavorable, as ...