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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Is it possible to estimate the abundance of conformers from J values?

I have a system of two disubstituted cyclohexanes and I want to estimate the abundance/ratio of the two based on the J values and if possible, roughly estimate the difference in free energy. To get ...
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How to find Gibbs energy for a real gas

I'm asked to find $\Delta G$ for the isothermal compression of $\ce{N2(g)}$ (real gas) at $0\ \mathrm{^\circ C}$ if the gas expands from $P=1\space\mathrm{atm}$ to $P=1000 \space\mathrm{atm}$. The ...
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Why does standard reduction potential get multiplied by the change in oxidation state and not by the number of electrons transferred?

The whole basis of Frost diagrams is to have a graphical representation of the Gibbs free energy of formation ($\Delta{G}_{f}$) of different oxidation states of an element using the proportional ...
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Thermodynamics: Solving for Entropy, Gibbs and Helmholtz

A reversible melting of $32.0\ \mathrm g$ of ice at $0\ \mathrm{^\circ C}$ and $1\ \mathrm{atm}$. Solve for $\Delta G, \Delta S_\text{universe}$, and $\Delta A$ I'm also given latent heat of fusion/...
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33 views

Is it possible to measure the entropy of a chemical reaction through calorimetry?

My broad question is how do you measure entropy change? I was doing a bit of digging into how thermodynamic tables are developed at I got this from NIST. Basically it seems like you need to indirectly ...
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Why does the plot of volume and temperature have a kink in a second order phase transition?

The $(b)$ part of the figure shows how thermodynamic variables change in a second order phase transformation. We observe there is a kink in the plot of volume with temperature. Why is that so? The ...
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128 views

How much energy water “captures” at it evaporates in room temperature?

As explained in Why does water evaporate spontaneously at room temperature despite ΔG > 0? water evaporates in room temperature because partial pressure of water is less than "standard" conditions ...
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378 views

NAMD free energy calculations (FEP, Alchemical)

I am trying to calculate the absolute free energy of a protein-ligand-complex using the free energy perturbation theory. Following the alchemical route in this tutorial, I have calculated eight MD-...
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50 views

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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491 views

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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103 views

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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669 views

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 $1.00~\...
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371 views

Delta G values for Pyruvate--> Alanine vs. Oxaloacetate -> Aspartate ->Asparagine

What are the delta G values for the mammalian (human) biosynthesis of alanine from pyruvate, and for the conversion of oxaloacetate to asparagine? (assuming no particular cellular restriction or other ...
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36 views

Is Gibbs energy minimized for processes at constant temperature are pressure only?

I've had this doubt for quite a while, This link https://chem.libretexts.org/Bookshelves/Physical_and_Theoretical_Chemistry_Textbook_Maps/Map%3A_Physical_Chemistry_for_the_Biosciences_(Chang)/04%...
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Calculating thermodynamic quantities for hydrogenation of iron nitride

HW#6.3 If the reaction $$\ce{Fe2N(s) + 3/2 H2(g) <=> 2 Fe(s) + NH3(g)}$$ comes to an equilibrium at a total pressure of $\pu{1 bar},$ analysis of the gas shows that at $\pu{700 K}$ and $\pu{800 ...
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56 views

Bond dissociation energy calculation

I am looking for methods to determine the dissociation free energy in a precise way, ideally from a simulations. My hope is to get the most precise values possible that are specific to the structure ...
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54 views

Is there any sort of correlation between melting point and the degrees of freedom for the molecules of a substance?

Suppose I had a solid whose molecules did not have rotational freedom. But if I were able to make it so that the molecules had rotational freedom ceteris paribus, is there a way to tell how the ...
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231 views

Gibbs Free Energy: Exothermic, low temperature & reduced system entropy - such reaction is spontaneous or not?

According to $\ce{\Delta G^\mathrm{o}= \Delta H^\mathrm{o} -T\Delta S^\mathrm{o}}$, if a reaction a) is exothermic, b) reduces system entropy, and c) the temperature is low, then it is spontaneous....
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Calculating the free energy of separation in AMBER

I am currently busy with my master's research project and I'm trying to calculate the free energy of separation of two cellobiose molecules in ionic liquid, that is, calculate the free energy of ...
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466 views

What does ΔG° refer to exactly?

My interpretation of this image is that $\Delta G^\circ$ is equal to the difference between $G^\circ$ of the products and $G^\circ$ of the reactants. But, I've also read $\Delta G^\circ$ as being ...
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68 views

Is chemical equilibrium possible at any temperature and pressure?

Consider the chemical reaction ${\rm Na+Cl\to NaCl}$ by mixing ${\rm Na}$ with ${\rm Cl}$ (or by mixing ${\rm NaOH}$ with some acid). This process is exothermic while the reverse ${\rm NaCl\to Na+Cl}$ ...
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Relationship between Yield and Applied Potentials

This question revolves around this question from Atkins' Chemical Principles 5th ed., Chapter 13, Question 13.116: Consider the electroplating of a metal $+1$ cation from a solution of unknown ...
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How do I get a value of the Gibbs energy of formation at 0 K and 0 bar?

The standard Gibbs free energy of formation for copper(II) oxide, $\ce{CuO}$, is $\Delta_\mathrm fG (\pu{298.15 K},\pu{1 bar}) = \pu{-129.7 kJ mol-1}$. How can I get $\Delta_\mathrm fG (\pu{0 K},\pu{...
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Find the standard Gibbs' free energy of formation at 298.15 K for O2 gas dissolved in the saturated aqueous solution?

The solubility of $O_2(g)$ in water at $25^o \text{C}$ and $\text{1 bar}$ pressure of $O_2(g)$ above the solution is $0.00126$ $mol$ $O_2(g)/kg$ $water$. Find $\Delta_fG_{298.15}^o(O_2(g),sln)$. I ...
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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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139 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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161 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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Given the Pair Correlation Functions for a Multi-component Fluid, is There a Simple way to Obtain the Helmholtz Free Energy?

I think it may not be possible. Given all the pair correlation functions, it seems possible to obtain the internal energy (assuming different species interact through pair-potentials (i.e. ...
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141 views

Why are non-polar hydrogens neglected in computational protein-drug binding studies?

Why are (non-polar) hydrogen atoms generally neglected in a protein-ligand (or drug) binding energy calculation? They do have charge and mass. Doesn't that affect the free energy calculation? The ...
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728 views

What is the name for the equation ΔG = ΔG° + RT ln Q?

As the title states, what is the name of the equation $$\Delta G=\Delta G^{\circ}+RT \ln Q$$ My textbook does not explicitly state the name and I could not find anything on google.
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bond energy calories

I am attempting to optimize interactions for a series of random and test molecules to a protein using docking software. The software uses QM/MMGBSA to calculate free energy in joules (yes it is not a ...
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100 views

Mathematical properties of free Gibbs energy

I'm wandering, if some mathematical properties of the free Gibbs energy (also called thermodynamic potential) are well known. For instance in chemistry, if $n_i^\alpha$ denotes the number of moles of ...
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Standard Gibb's Free energy change, standard state and equilibrium

I just want to confirm if I am right in thinking that: statement: When a reaction in standard state is in equilibrium, then equilibrium constant K=1 Reason: since in a equilibrium, $Q=K$ and $ΔG=0$. ...
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Entropy and Gibbs Free Energy of Chelate Complexes

Of [Cd(NH2CH3)4]2+ and [Cd(en)2]2+ the stability of the latter is higher than the former attributing to chelation in the en complex .This is evident from the fact that the Gibbs Free Energy change for ...
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How to use anodic and cathodic overpotentials to calculate electrolytic energy efficiency?

I am trying to calculate the energy efficiency for $\ce{CO2}$ reduction to formate, coupled to water oxidation based on literature data. $$\ce{CO2 + 2e- + 2H+ -> HCOOH}$$ $$\ce{H2O -> 2H+ + 1/...
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How to derive thermodynamic activity?

From wikipedia thermodynamic activity is given as $$ a = \exp(\frac{\mu - \mu_{0}} {RT})$$ which becomes, $$ RT\ln(a) = \mu - \mu_{0}\tag{1}$$ And i have to do a calculation where activity is given as ...
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How to find entropy of chemical network reaction?

I have the following system of reactions: $$ \begin{aligned} \ce{X_1 + Y_1 &<=>[$k_{21}$][$k_{12}$] X_2} \\ \ce{X_2 &<=>[$k_{32}$][$k_{23}$] X_3} \\ \ce{X_3 &<=&...
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Gibb's energy change for system

Heat liberated by a given amount of an ideal gas is $\pu{1200 cal}$ at $\pu{300K}$. What is the Gibbs free energy change for the gas in this process? My attempt: I know that for a reversible process ...
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293 views

Calculating Gibbs free energy for the reaction of burning methanol

Calculate $Δ_\mathrm{r}G^\circ$ for the following reaction: $$\ce{2 CH3OH(l) + 3 O2(g) -> 2 CO2(g) + 4 H2O(l)}$$ using $Δ_\mathrm{r}H^\circ$ and $Δ_\mathrm{r}S^\circ$ at $\pu{298.13 K}$ $(\pu{25 °C}...
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Reaction energies of solids from quantum chemistry?

I was reading a paper by Catlow et al. [1], and they mentioned the dissolution of copper into copper ions, which is given by this equation: $$\ce{Cu2O(s) + 2 h+ <=> Cu+(aq) + 1/2 O2(g)} \tag{...
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Gibbs free energy of phosphorus pentachloride decomposition reaction

The equilibrium constant at $\pu{227 °C}$ for the equation $$\ce{PCl5(g) <=> PCl3(g) + Cl2(g)}$$ is $K_p = \pu{4.50E3 bar}.$ Calculate the value of $Δ_\mathrm{rxn}G^\circ$ at $\pu{227 ...
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Gibbs energy at a certain temperature

For the reaction $$\ce{1/2 N2(g) + 3/2 H2(g) -> NH3(g)}$$ $ΔG$ at $\pu{298.15 K}$ is $\pu{-3980 cal},$ and the change in enthalpy is given by the expression: $$ΔH = -9.19 - 7.12T + 3.182\cdot 10^{-...
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Why is Helmholtz free energy often defined as the useful work attainable at constant volume if constant volume implies no expansion?

From Wikipedia: "In thermodynamic systems where the temperature and volume are held constant, the measure of useful work attainable is the Helmholtz free energy function" https://en.wikipedia.org/wiki/...
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How is the change in Gibb's free energy a condition for spontaneity for reactions not happening under constant pressure conditions?

According to what I have studied, the change in Gibb's free energy is only a condition for spontaneity for processes happening at constant pressure and temperature conditions. Consider a reversible ...
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Finding Gibbs energy at different temperatures just given Gibbs energy at one temperature

How would it be found the Gibbs energy at a certain temperature, if they just give you another Gibbs energy at a temperature? For example: Given $\Delta G = -230 Kcal/mol$ at $773K$ for the reaction $...