Also known as Gibbs energy, it is the enthalpy minus the product of thermodynamic temperature and entropy.
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57 views
What do the variables in expression for Gibbs energy represent [on hold]
I am substituting $\Delta H/T$ for $\Delta S$ and then cancel $T$ in $T\Delta S$ and that always gives me $\Delta G=0$. I know I am doing a mistake with that, but which?
I am basing my assumptions ...
0
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0answers
62 views
Why does a EMF measurement deliver standard state values?
In the literature one can often find the following equation for the determination of standard Gibbs Energies of Formation with emf measurements:
$$\Delta_f{G}^\circ = -zFE$$
I don't understand why ...
1
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1answer
103 views
Connection between Gibbs Energy of Formation and Gibbs Energy of Mixing
Recently I found the following formula, which I cannot verify to be correct. Since I found this formula in several publications I assume that it is correct but I don't know why.
First there is the ...
1
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0answers
51 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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1answer
51 views
Is the stoichiometric coefficient equivalent to the mole fraction?
I have a small problem to understand (or distinguish between) two concepts of free mixing enthalpy.
In several textbooks, I found the following formula for the molar free mixing enthalpy (binary ...
0
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0answers
35 views
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 ...
3
votes
2answers
98 views
Proof of the chemical potential formula
My textbook as well as Wikipedia both state the formula $\mu_A = \mu_A^0 + RT\ln\{A\}$ which gives the chemical potential $\mu_A$ of a chemical species $A$ as function of the standard chemical ...
1
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1answer
47 views
Is work done by a system negative delta G or positive delta G?
My textbook states that a process is spontaneous and can perform work only when it is moving toward equilibrium. Since the process is spontaneous, wouldn't that mean that the work done is attributed ...
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2answers
150 views
Could a non-spontaneous reaction occur “on its own”?
Does spontaneity really only apply to the net free energy change of a reaction?
I used to be taught that spontaneous reactions could occur on their own BUT without enzymes or a spark they might take ...
0
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1answer
85 views
Energy at constant Entropy and Volume
The system of constant entropy and constant volume will attain the equilibrium in a state of minimum energy. Why?
I know that:
$\Delta G= \Delta H-T\Delta S$
And at constant volume and entropy: $\...
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1answer
131 views
Calculate Heat of Atomisation [closed]
What is heat of atomisation of P4O6(s) Given heat of sublimation of P4O6 is x kJ/mol & P–O bond energy is y kJ/mol.
What is heat of atomisation of P4O6(s) Given heat of sublimation of P4O6 is x ...
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0answers
101 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 ...
3
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1answer
93 views
Why isn't standard Gibbs free energy always zero?
I read in my textbook that one of the standard conditions we should use when calculating the standard Gibbs free energy is having a concentration of 1 M of all the reagents and the products in the ...
1
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0answers
49 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 ${\rm NaCl\to Na+Cl}$ ...
2
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2answers
131 views
What are the units that measure free energy?
Is it $\pu{kJ/mol}$? I have done problems and I always end up with these units, but is this correct?
3
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2answers
163 views
How come ∆G ≤ 0 is used for spontaneity in electrochemistry, not ∆G ≤ W(other)?
The spontaneity condition for a system at constant temperature and pressure in which the only type of work accomplished is of the $pV$ type can be expressed as:
$$\Delta G\le0\tag1$$
In case of ...
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0answers
23 views
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 ...
7
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4answers
4k views
Why is entropy favorable?
I cannot seem to grasp the logic behind it. We say that more entropy (or more disordered system) is favorable over less entropy. But why? Why is randomness preferred over proper arrangement of atoms/...
2
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1answer
765 views
Is the Haber Process here proceeding at positive Gibbs free energy change?
$\ce{3H2 + N2 -> 2NH3}$ is the forward reaction used in the Haber process, the industrial production of ammonia. After studying Gibbs energy and how it is just another way of saying that the 2nd ...
6
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1answer
67 views
Biomolecular energy functions and entropy
From what I've been reading, it seems that entropy (rather than enthalpy) is the biggest driver of protein folding (especially the burying of hydrophobic residues). However, popular energy functions ...
1
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0answers
60 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 ...
2
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1answer
303 views
Physical Explanation for variation of Gibbs Free Energy with Temperature and Pressure
Reading Atkins Elements of Physical Chemistry right now, and the book says:
"At constant pressure and entropy, an increase in temperature ($\Delta T\gt0$) results in a decrease in $G_\mathrm m$ (molar ...
3
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1answer
268 views
Why can we use standard entropy when determining temperature at which a reaction becomes spontaneous?
In this chemistry problem, $\Delta H$ and $\Delta S$ are given at $298\text{ K}$, and it asks for the temperature at which the reaction becomes spontaneous:
For the reaction $2\text{SO}_3 \...
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0answers
66 views
Find occurrence of a peptide stereoisomer knowing Gibbs energy of trans-cis transition
What is the % occurrence of cis-Glu-Pro peptide linkage if $\Delta G_{\text{trans-cis}} = \pu{0.5 kcal/mol}$?
My attempt at this:
\begin{align}
\Delta G &\approx 1.4\, \mathrm{p}K\\
\mathrm{p}K &...
2
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3answers
1k views
What is the difference between “spontaneous” and “energetically favourable”? [duplicate]
I read somewhere that the difference between energetically favorable reactions and spontaneous reactions is that energetically favorable reactions are ones where energy is released, i.e., $\Delta H<...
2
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1answer
72 views
Discrepancies in calculating free energy values listed in Stumm and Morgan
I am hoping someone can help me with a clarifying a calculation on a fundamental thermodynamic understanding of reactions. Below is Table 2.5 from Stumm and Morgan's Aquatic Chemistry.
Table 2.5. ...
5
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0answers
383 views
Entropy of Activation and Temperature Dependence
I am trying to understand the extrapolation of enthalpy $\Delta H^{\ddagger}$ and entropy of activation $\Delta S^{\ddagger}$ from the Eyring equation. It's typically cast as: $$ln(k/T) = -\Delta H^{\...
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1answer
96 views
How did Williard Gibbs come up with the Gibbs equation?
The equation I am referring to is
$$\Delta G = \Delta H - T\Delta S$$
I understand that this Gibbs free energy determines if a process is spontaneous or not. My question is how did Williard Gibbs, ...
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0answers
50 views
How do I get a value of the Gibbs energy of formation at 0 K and 0 bar?
The standard Gibbs free energy of formation for copper(II) oxide, $\ce{CuO}$, is $\Delta_\mathrm fG (\pu{298.15 K},\pu{1 bar}) = \pu{-129.7 kJ mol-1}$.
How can I get $\Delta_\mathrm fG (\pu{0 K},\pu{...
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0answers
74 views
Change of notation in calculating Gibbs free energy
I am learning physical chemistry on my own, and I understand everything except for the underlined part.
Specifically, why does the prefactor change from $\frac{1}{V}$ to $\frac{1}{V_1}$?
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2answers
151 views
To what microscopic quantity does Gibbs energy correspond to?
Is the Gibbs energy of a system equal to the potential energy of a system? The answers to this and this questions seem contradictory. Also, this does not seem to tell that Gibbs energy is equal to the ...
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2answers
325 views
Can we force reactions with positive delta G?
Do these reactions always have to be paired with another energetically favorable reaction with a greater delta G magnitude, or is there a way to force reactions with a positive delta G to happen?
8
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1answer
437 views
Why is $\Delta G = -T \Delta S_{\mathrm{total}}$ valid only at constant pressure?
According to my book(Elements of Physical Chemistry by Atkins and de Paula, 5th ed.), $\Delta G = - T \Delta S_{\mathrm{total}}$ is valid only for constant pressure and temperature.
Enthalpy is ...
3
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1answer
89 views
Equilibrium and Free Energy
$$\ce{CO2(g) + Ca^2+(aq) + H2O(aq) <=> CaCO3(s) + 2H^+(aq)}$$
Find the equilibrium constant using a free energy table.
Finding the free energy and plugging it into the equation $\mathrm{G =...
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1answer
138 views
Why does the standard enthalpy of formation diverge so far from the standard Gibbs free energy of formation for some substances?
If you look at a Table of Thermodynamic Values for chemical substances, most substances have very close values for their standard enthalpy of formation ($\Delta H_{\mathrm{f}}^\circ$) and their ...
3
votes
2answers
285 views
Why energy of some intermediates of glycolysis increases?
It is possible that I do not understand the concept of energy, but according to the diagram in my book, the energy between steps 4 and 5 and between 6 and 8 increases. How is this possible? Also, as ...
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1answer
3k views
How to calculate Gibbs free energy from pKa?
Is it possible to calculate Gibbs free energy ($ΔG = -RT\ln K_{eq}$) of an acid dissociation reaction using the $\mathrm{pK_a}$? If so, how?
2
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1answer
229 views
Gibbs free energy=potential free energy? (Transition state theory)
Online I found the plot Gibbs free energy vs. reaction coordinate:
https://en.wikipedia.org/wiki/Transition_state_theory
and on many books I found the plot potential energy vs. reaction coordinate (...
3
votes
1answer
130 views
Are all reactions with ΔG < 0 spontaneous?
Given the formula $\Delta G = \Delta H - T\Delta S$. It is commonly written that all spontaneous reactions necessarily have $\Delta G < 0$. I was curious if the converse is true: Are all reactions ...
6
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2answers
386 views
Thermodynamics: Relation between different types of energy: My Analogy
I have always been confused between the different kind of energies in thermodynamics so today I thought of finally getting it right. Here's my analogy(which is wrong and I need help in improving it, ...
2
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1answer
132 views
How can absolute binding free energies be calculated?
In the calculation of binding free energies, such as between a protein and a ligand, I learned that absolute values cannot be obtained from simulation (such as taught in this lecture, slide 2). Rather,...
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0answers
254 views
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/...
12
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3answers
193 views
Why can't a reaction go to completeness?
What is the reason for why an exergonic reaction would still have some remaining reactants (or an endergonic reaction to have any products)? The explanation given on this page (see Chemical reactions ...
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2answers
283 views
Why Gibbs free energy is equating to 0?
I have studied thermodynamics, in which the infamous Gibbs equation came.
$$ \mathrm{d}G = \mathrm{d}H - T\,\mathrm{d}S $$
Then my book said the criteria of spontaneity based on gibbs energy is at ...
5
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2answers
1k views
Why are condensation reactions endergonic?
My lecture notes state that
Condensation reactions, like all biosynthetic reactions, are endergonic.
I am unsure as to why this would be the case. I thought bond formation was an exothermic ...
1
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0answers
707 views
Find the standard Gibbs' free energy of formation at 298.15 K for O2 gas dissolved in the saturated aqueous solution?
The solubility of $O_2(g)$ in water at $25^o \text{C}$ and $\text{1 bar}$ pressure of $O_2(g)$ above the solution is $0.00126$ $mol$ $O_2(g)/kg$ $water$. Find $\Delta_fG_{298.15}^o(O_2(g),sln)$.
I ...
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3answers
6k views
How to derive the Gibbs free energy for an ideal gas?
Determine the Gibbs Free Energy for an ideal gas and show that, this energy, and its derivate can be related to the enthalpy of the system via Gibbs-Helmholtz equation
$$H = -T^2 \left( \frac{\...
4
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2answers
177 views
What is the source of discrepancy in the calculation of Standard State Gibbs Free Energy change of the reaction of HCl (l) dissolving in water?
I have calculated $\Delta_\text{r} G^o$ two different ways and got completely different results. Why? What assumptions have I made incorrectly, particularly in the first calculation shown below?
...
3
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1answer
403 views
Can I solve the partial derivative (dG/dH)s ? Does it make sense?
It is possible to express , in terms of Cp, Cv, V, P, kt etc. ?
I know that G and H are both derived from the Legandre transformation of U, so they are the same equivalent representation of ...
3
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0answers
295 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-...
