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2
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1answer
29 views

Can a reaction with positive Gibbs free energy change ever occur?

If you have an endothermic reaction with a negative entropy change, is it still possible to induce the reaction in some way despite the fact that the Gibbs free energy change is positive or all ...
1
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2answers
50 views

Gibbs free energy or reaction enthalphy

If I conduct a reaction say, $$\ce{CaO(s) + H2O(l) \rightarrow Ca(OH)2 (aq)}$$ let us say , I want to measure the energy generated from the reaction.Will this energy I calculate equal the change in ...
4
votes
1answer
83 views

Gibbs Free Energy : What is it trying to say actually?

"Gibbs Energy is the useful work that can be extracted from the heat of a rxn or a thermodynamic process." I understand how it predicts the feasibility of a chemical rxn, considering the Entropy ...
4
votes
2answers
74 views

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 ...
4
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3answers
56 views

What value of temperature does T represent in Gibbs Free Energy Equation?

Temperature before, or after reaction? Temperature change? Or what is it?
0
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2answers
35 views

Why is dG=dH-TdS?

I get that $G=H-TS$ because then: $dG=dH-TdS-SdT=TdS+VdP-TdS-SdT$. Therefore, by cancelling: $dG=VdP-SdT$ which is the equations for dG. However, I cant get this result from using $dG=dH-TdS$. ...
5
votes
1answer
92 views

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 ...
3
votes
1answer
65 views

Calculating the Gibbs Free Energy of Mixing

This is a Physical Chemistry Question and comes from the Atkins Physical Chemistry book. The answers are given but I don't understand how to get to $-9.7~\mathrm{kJ}$ for the first part of the ...
3
votes
1answer
50 views

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 ...
3
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0answers
45 views

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 ...
4
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1answer
25 views

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 ...
2
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0answers
55 views

How to find Gibbs energy for a real gas

I'm asked to find $\Delta G$ for the isothermal compression of $N_{2(g)}$ (real gas) at $0°C$ if the gas expands from $P=1\space atm$ to $P=1000 \space atm$. The fugacity coefficients are ...
2
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0answers
57 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 ...
1
vote
2answers
266 views

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 ...
0
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0answers
39 views

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

Why are (Non-polar) Hydrogen 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?
0
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0answers
56 views

Name the equation $\Delta G=\Delta G^{\circ}+RT \ln Q$

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.
0
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1answer
35 views

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 ...
3
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3answers
154 views

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 ...
0
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2answers
67 views

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.
3
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1answer
886 views

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 ...
1
vote
1answer
149 views

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 $f_i$ ...
1
vote
1answer
67 views

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 ...
1
vote
1answer
73 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 = \text{RT} ln ...
4
votes
1answer
193 views

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 ...
1
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1answer
107 views

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 $\Delta\mathrm{G}$ ...
2
votes
1answer
463 views

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 ...
2
votes
1answer
2k views

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!
2
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2answers
2k views

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 ...
8
votes
2answers
762 views

Transition state and free energy

I would appreciate if someone could clarify this for me. We have products A+B combining to form C+D through the transition state X. First of all, are all reactions at least virtually reversible? Is ...
0
votes
0answers
75 views

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 ...
12
votes
3answers
17k views

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 ...
0
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1answer
298 views

Software Bond Dissociation Energies, Bond Energy and Hybridization with Polarity

I want to calculate BDE to measure the cost of hybridization of two molecules. There are many examples of protein ligand docking on the internet but there are no examples of hybridization of ligand to ...
0
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1answer
388 views

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 ...
2
votes
1answer
710 views

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 ...
4
votes
1answer
413 views

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: ...
2
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0answers
197 views

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? ...
1
vote
1answer
125 views

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 ...
4
votes
1answer
1k views

How to calculate the solubility of CaF₂ at different temperatures?

By 25° Celsius, I used the free energy table for $\small G$ for the reaction and got $\small K_{sp}= 10^{-9.02}$. I now need to find out what the solubility is by 10, 20 and 30°C. Could you ...
1
vote
0answers
38 views

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 ...
3
votes
2answers
540 views

How do I find change in Gibbs free energy of this reaction?

How do I find the change in Gibbs free energy of the reaction $\ce{H_2 + \frac{1}{2}O_2 -> H_2O}$ when it is at $\ce{75}$°$\ce{C}$ and $\ce{1 atm}$. Do I calculate the Gibbs free energy of each ...
10
votes
1answer
1k views

What does “reaction coordinate” mean?

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. ...
9
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1answer
1k views

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 ...
14
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2answers
992 views

Gibbs free energy-minimum or zero?

A reaction proceeds towards the direction of lesser Gibbs Free energy (at constant T and P). So, we could say that Gibbs free energy at equilibrium is minimum. On the other hand, we have $$\Delta ...