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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Finding the temperature at which the system reaches equilibrium
I’m really stuck on this problem. This involves dissolving Borax:
$$\ce{Na2B4O7•10H2O(s)<=>2Na^+(aq) + B4O7^2-(aq) + 10H2O}$$
$$\begin{align}\Delta H&=\pu{109 kJ/mol} \\ \Delta S&= \pu{...
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How to explain disagreement between Le Châtelier's principle and the simplified Gibbs free energy equation?
For example, for the dissolution of a salt in water that is exothermic, heating the solution would drive the reaction towards the solid form of the salt according to Le Châtelier's principle.
However,...
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How to calculate the variation of the standard reaction enthalpy for the CO, CO2, H2O, H2 equilibrium?
For the reaction
$$\ce{CO2 (g) + H2 (g) <=> CO (g) + H2O (g)}$$
the equilibrium constant $K_p$ has a value of $0.534$ at $\pu{960 K}$ and $1.571$ at $\pu{1260 K}$. Calculate the variation of ...
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1answer
45 views
Relation between equilibrium constant and entropy change
Like the Van't Hoff equation, which relates change in enthalpy to equilibrium constant, is there a similar equation for the relation between change in entropy and equilibrium constant?
Consider the ...
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Reaction quotient and Gibbs free energy at the start of a reaction
According to the equation 33 above, shouldn't be all the reactions be spontaneous initially? Because the reaction quotient Q, is zero at the start of the reaction and logarithm of Q makes it a very ...
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If change in free energy (G) is positive, how do those reactions still occur?
I was doing a couple of problems for homework:
Calculate $K_\mathrm{sp}$ of $\ce{AgI}$ at $55.0\ \mathrm{^\circ C}$
Calculate $K_\mathrm{b}$ of $\ce{NH3}$ at $36.0\ \mathrm{^\circ C}$
I have to use ...
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Gibbs energy at a certain temperature
For the reaction
$$\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....
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2answers
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Is temperature double-counted in the Gibbs free energy equation?
Complete amateur here. When looking at one form of the equation deriving the change in Gibbs free energy for a given chemical reaction, the terms change in enthalpy, and the negative product of ...
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1answer
36 views
Change in heat of photosynthesis
Consider a plant that uses the energy it receives from the sun to do work (to undergo photosynthesis) to produce glucose. The minimum amount of work this plant can do to produce 1 mole of glucose is ...
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1answer
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Gibbs Free Energy Notation
What's the difference between $G$, $\Delta G$, $\Delta G^\circ$, and $\Delta_\mathrm r G^\circ$?
I've seen the first two used interchangably, and seen $G$ specifically referred to as change in Gibbs ...
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Derivation of relationship betwee standard Gibbs energy of reaction and equilibrium constant? [closed]
How does one derive $\Delta_\mathrm r G^\circ = -RT\ln(K)$? I don't see the connection mathematically or conceptually; how does Gibbs at all relate to the equilibrium constant of a reaction?
This was ...
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Heat and work of glucose combustion
$$\ce{C6H12O6(s) + 6 O2(g) -> 6 CO2(g) + 6 H2O(g)}$$
When looking at glucose combustion I found that the change in Gibbs free energy is greater than the change in enthalpy. If we assume the process ...
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1answer
94 views
Gibbs Free Energy and Maximum Work
I am a high school student and my professor mentioned that the Gibbs free energy is the maximum amount of work (or useful work) that a system can do, whereas entropy is a measure of the non-available ...
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2answers
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Why is my conclusion inconsistent with the van't Hoff equation?
Let's say I hypothesize that a graph of $\ln K$ vs. $1/T$ has a slope of $-∆G^\circ/R$ and a $y$-intercept of $0$. I prove it simply:
$$∆G^\circ = -RT\ln K \quad\to\quad \ln K = -\frac{∆G^\circ}{RT}$$...
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1answer
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Change in Gibbs free energy vs. change in enthalpy
When learning about other thermodynamic quantities, like $\Delta H$, I was taught that this represents the energy absorbed or released by a system after the reaction has gone 100% to completion. For ...
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2answers
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Derivation of Gibbs free energy formula
Okay, so I'm trying to derive an important formula which states that -
∆G(r) = ∆G° + RTln( RQ )
where ∆G(r) is the instantaneous rate of change of Gibbs energy with ...
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2answers
37 views
Where does Free Energy go in a Redox Reaction?
This doubt came to my mind while answering the following question:
Why does a voltaic cell not operate unless the two separate compartments are connected by an external circuit?
The answer seems ...
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1answer
163 views
Gibbs free energy of formation vs. Gibbs free energy of reaction?
Consider the following reaction:
$$\ce{A(s) + B(s) <=> AB(s)}.$$
I know there might be kinetic limitations but I am only interested in thermodynamic relations.
In general, the Gibbs free ...
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2answers
294 views
Gibbs Free energy of a reversible reaction
From what I understand, it sounds like the Gibbs Free Energy change of a reversible reaction at equilibrium is zero. However, since I know that Gibbs Free energy change depends on temperature, does ...
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2answers
270 views
Gibbs free energy in standard state vs. equilibrium
I have a problem with the definition of the standard Gibbs energy and its connection to the equilibrium constants.
I think, that I've basically understood what the different equation mean but there ...
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Conversion of graphite into diamond [duplicate]
The standard state Gibbs free energies of formation of C(graphite) and C(diamond) at $T = \pu{298 K}$ are $\pu{0 kJ mol-1}$ and $\pu{2.9 kJ mol-1}$, respectively.
The conversion of graphite [C(...
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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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2answers
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What is the Gibbs free energy difference between conformational states
In statistical mechanics, for a system of $N$ particles $x_1, \ldots, x_N$ in three dimensions, the Gibbs free energy is defined in terms of the Hamiltonian $H$ as
$$ G = -k_\mathrm B T \log \int_{\...
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2answers
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Why proton concentration is divided by 10⁻⁷?
I am reviewing the book Biochemistry Concepts and Connections by Appling, Cahill, and Mathews and I cannot understand why they divide by the hydrogen concentration by $10^{-7}$. Why not just leave it ...
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1answer
157 views
Find the minimum temperature at which the reaction will become spontaneous [closed]
This question came in my entrance exam and I think 273 K should be the answer because the reaction is already spontaneous. I just want to know if I've attempted it correctly.
For a certain ...
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1answer
193 views
Pressure at which graphite and diamond are in equilibrium
I came across this problem :
The standard state Gibbs free energies of formation of C(graphite) and C(diamond) at $T = \pu{298 K}$ are $\pu{0 kJ mol-1}$ and $\pu{2.9 kJ mol-1}$, respectively.
...
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2answers
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Calculate Gibbs energy of dinitrogen pentoxide using its vapor pressure and sublimation
I am having trouble with the following problem:
Dinitrogen pentoxide, $\ce{N2O5}$, is a solid with a high vapor pressure. Its vapor pressure at $\pu{7.5 °C}$ is $\pu{100 mmHg}$, and the solid ...
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1answer
118 views
Free energy of solvation and Henry's law constant
I am trying to calculate the free energy of solvation of $\ce{CO2}$ from its Henry's law constant. As given on Wikipedia, the dimensionless Henry's law constant is $0.83$. If I try to calculate $\...
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1answer
74 views
How to calculate the standard Gibbs energy at equilibrium?
Given that $K_c = 1.7 \times 10^{-13}$, calculate $\Delta G^{\circ}$ for this equilibrium mixture at $\pu{298 K}$.
$$\ce{N2O (g) + \frac{1}{2}O2 (g) <=> 2 NO (g)}$$
I've calculated:
$$
\...
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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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2answers
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How to derive the relation between gibbs energy and equilibrium constant?
I want to understand the derivation between gibbs energy and equillibrium constant $$\Delta G=\Delta G^o+RT\ln Q?$$
I have seen a similar post on CSE Derivation of relationship between equilibrium ...
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1answer
132 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 ...
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0answers
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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
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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 ...
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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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2answers
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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 ...
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1answer
566 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
403 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 ...
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1answer
145 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
547 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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306 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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1answer
270 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 ...
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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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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?
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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
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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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4answers
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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/...
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2answers
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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 ...
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1answer
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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 ...
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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 ...
