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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Heat given off from an electrochemical cell compared to mixing reactants

My confusion regarding the difference between the heat given off in a reaction that takes place in an electrochemical cell compared to in a beaker/appropriate container when the reactants are simple ...
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What value of temperature does T represent in Gibbs Free Energy Equation?

Temperature before, or after reaction? Temperature change? Or what is it?
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Why is dG = dH − TdS?

I get that $G=H-TS$ because then: $$\begin{align}\mathrm dG&=\mathrm dH-T\,\mathrm dS-S\mathrm dT\\&=T\,\mathrm dS+V\,\mathrm dp-T\,\mathrm dS-S\,\mathrm dT\end{align}$$ Therefore, by ...
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Why is Gibbs free energy more useful than internal energy?

$$\mathrm{d}U<T\,\mathrm{d}S-p\,\mathrm{d}V= \left(\frac{\partial U}{\partial S}\right)_{\!V}\,\mathrm{d}S +\left(\frac{\partial U}{\partial V}\right)_{\!S}\,\mathrm{d}V$$ So for a change to occur ...
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Calculating the Gibbs Free Energy of Mixing

This is a Physical Chemistry Question and comes from the Atkins Physical Chemistry book. Suppose that $2.0~\mathrm{mol}$ $\ce{H2}$ at $2.0~\mathrm{atm}$ and $25~^\circ\mathrm{C}$ and $4.0~\mathrm{...
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Why is it necessary to consider infinitesimal changes in p,V,T for H,U and G given that they're state functions?

State functions such as $G$ only depend on the state of the system and are not dependent on the "path" that took the system to that state (which would be the case for work, for example, which is not a ...
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How to derive the pressure dependency for the Gibbs free energy?

$$\mathrm{d}G=\left(\frac {\partial G}{\partial p}\right)_T+\left(\frac {\partial G}{\partial T}\right)_p$$ The above is an exact differential. Firstly what does this mean physically? (I hear about ...
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How can -G/T and -A/T be thought of as 'disguised' entropies?

I understand that entropy is defined as $\mathrm{d}S=\mathrm{d}q/T$ for a reversible change but I fail to see why $-G/T$ and $-A/T$ can be thought of as 'disguised' entropies. This is a question on my ...
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How is the energy of reactants in a chemical reaction found ?

A pretty rudimentary question, but I'm reviewing the concept of energy diagrams and activation energy and I'm curious to know how chemists find the energy of reactants and of a transition state in a ...
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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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Regarding the free energy requirements for reacting gases

Continued from my previous question here. With regards to the Boltzmann factor, I am confused on what type of terms we can substitute for E. I know kinetic energy is one, free energy as well, but ...
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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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What is the correct definition of the Gibbs free energy of activation?

Is the following correct? Gibbs free energy of activation is used in energy profiles where the stabilities of the species are expressed as changes in Gibbs energy, while the activation energy Ea is ...
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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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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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Is it possible for a reaction to have an entropy change of zero?

If the question seems rather "unscientific", be kind to accept my apology. My textbook is being highly unclear about the topic and I need to know the answer to this question before I go on with my ...
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Is there a reason for the mathematical form of the equilibrium constant? [duplicate]

Why are the two molarities multiplied and not added, and why is each raised to the power of the coefficient rather than multiplied by it? What is the reasoning behind this form? Was it simply ...
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Rate-limiting in transition state theory

Suppose an initial state $A$ can transition to either state $C$ or state $D$. Suppose further that both of these two processes are rate-limited by a transition to the same intermediate state $B$, as ...
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How is it thermodynamically possible to obtain energy from a piece of coal?

If we put a piece of coal in open air we don't get any energy of it. But if we put fire to it in open air we get energy. Explain it with help of Gibbs free energy.
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What is the difference between enthalpy of formation and Gibbs free energy of formation?

I'm having trouble (not alone, apparently) understanding the concept of Gibbs free energy, but I'm beginning to. What I still don't understand, however, is how Gibbs free energy of formation differs ...
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Proving RTln($a_i$) equal to non PV work done by system,where $a_i$ is activity

We know that chemical potential is defined as ${\mu}_i={\mu}_i^{standard}+RT\ln(a_i)$. Here $a_i$ is the activity of $i^\text{th}$ component of solution. In case of gases instead of $a_i$ it is $f_i$ (...
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What kind of equilibrium constant we use for Gibbs free energy and Van't Hoff equation?

We know that the Gibbs free energy is related to the equilibrium constant by the following equation: $$\Delta_\mathrm{r}G^\circ=-RT\ln K$$ We also know the Van't Hoff equation: $$\ln\left(\frac{K_2}{...
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What is the energy change of ethene reacting with hydrogen gas?

$\ce{CH2CH2(g) + H2(g) -> CH3CH3(g)}$ Using this table, source: http://www.kentchemistry.com/images/links/Kinetics/TB08_003.GIF ...
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361 views

Why isn't ΔG equal to zero for this equilibrium reaction?

In the reaction $\ce{E(g) <=> P(g)}$ at 25 °C, equilibrium is reached when the pressure of the product is 0.100 that of the reactant. What is $\Delta G$ in joules? Using $\Delta G = RT\ln K$, ...
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Activated Complex Products/Reactants

We know that an activation complex is the temporary unstable compound formed when activation energy is reached. But what dictates whether the products are indeed going to be products or if they become ...
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Clarifications on the calculation of the $\Delta\mathrm{G}$ of a reaction

I'm trying to calculate the $\Delta\mathrm{G}$ of the following reaction. Are my calculations correct? I'm also a bit puzzled, 'cause this is a endoergonic reaction right? But the $\Delta\mathrm{G}$ ...
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Determining standard Gibbs free energy for water?

I am dealing with the dissociation of water into its components hydrogen and oxygen and I am trying to determine the standard Gibbs free energies of each component. My professor said if the substance ...
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What is chemical free energy?

What is chemical free energy? How can we practically explain its existence? How can it be used to do some useful work like in an electrochemical cell? I couldn't understand clearly about it when I ...
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how is the relation between Gibbs free energy and cell potential?

First of all what is exactly Gibbs free energy in regards to an electrochemical process? How can we visualise it? How does Gibbs free energy change in an electrochemical reaction? How is it related to ...
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Derivation of relationship between equilibrium constant and Gibbs free energy change

Why is $\Delta G=\Delta G^o+RT\ln Q?$ It feels like all online sources were written for introductory Chemistry students! Where do I find a rigorous proof of this identity? Greatly appreciate it!
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Derivation of relationship between Gibbs free energy and electrochemical cell potential

Why is $\Delta G = -nFE$? I don't understand what the motivation is behind this definition. Was it derived or just given? The textbook provides no justification for this equation. In fact, much of ...
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Transition state and free energy

We have products $\ce{A + B}$ combining to form $\ce{C + D}$ through the transition state $\ce{X}$. Are all reactions at least virtually reversible? Is the difference between a reversible reaction ...
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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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Difference between exothermic and exergonic

In High School I learned that an exothermic reactions releases energy, while an endothermic reaction needs energy to occur. Now I learned that there is a separate, somewhat similar classification ...
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Calculating bond disassociation energy and bond energy for ATP [closed]

I'd like to calculate Bond Dissociation Energy and Bond Energy for ATP to a similar molecule. What free (at least for academic use) computer programs which natively support and document BDE? If you ...
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Is the activation barrier of a reaction related to the free energy or heat of formation of its reactants?

The energy barrier for activation appears in the derivation of a bimolecular reaction through collision or transition state theory, but it seems that from looking at diagram such as this one it seems ...
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How is hydration free energy of a solute measured experimentally?

I am reading a paper (Shirts, M. R.; and Pitera, J. W. and Swope, W. C. and Pande, V. S. J. Chem. Phys. 2003, 119, 5740-5761). Near the beginning of the paper (page 5745), the authors state: ...
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Minimizing Gibbs free energy with Helmholtz free energy expressions

If I have an expression for the Helmholtz free energy (from statistical associating fluid theory for a polymer system), can I still find the Gibbs free energy minimum under constant $T,P$ conditions? ...
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Software for chemical reaction simulation in ICE

I want to study what happens in a internal combustion engine in which fossil fuels are mixed along with other chemical additives. Example: Acetone drastically reduces surface tension. Most fuel ...
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How to calculate the solubility of CaF2 at different temperatures?

At $\pu{25^\circ C}$ I used the free energy table for $G$ for the reaction and got $K_\mathrm{sp}= 10^{-9.02}$. I now need to find out what the solubility is at $10$, $20$ and $\pu{30^\circ C}$. ...
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Should the anode potential be increased or decreased to generate current?

I am taking a course on fuel cells and we were talking about the activation energy needed to start a chemical reaction. I would think that the answer to this question is that the anode potential ...
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How do I find change in Gibbs free energy of water formation?

How do I find the change in Gibbs free energy of the reaction $$\ce{H2 + \frac{1}{2}O2 -> H2O}$$ when it is at $\pu{75^\circ C}$ and $\pu{1 atm}$? Do I calculate the Gibbs free energy of each ...
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What does “reaction coordinate” mean? What does it mean when a reaction has TWO reaction coordinates?

I'm familiar with the concept of a reaction coordinate from high school chemistry as some generic conformational parameter that all of the intermediate states of a chemical reaction lie upon. Recently,...
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How are $\sigma$ and $\sigma^\pm$ determined in Hammett plots?

The Hammett plot is commonly invoked in organic chemistry to reason about the plausibility (or implausibility) of various reaction mechanisms. The vertical axis is essentially the logarithm of an ...
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Gibbs free energy-minimum or zero?

A reaction proceeds towards the direction of lesser Gibbs free energy (at constant $T$ (temperature) and $P$ (pressure)). So, we could say that Gibbs free energy at equilibrium is minimum. On the ...

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