Questions tagged [entropy]
For questions about the thermodynamical state function entropy, commonly understood as a measure of disorder.
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questions
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At equilibrium, which one of the following is always Zero? [duplicate]
At equilibrium, which one of the following is always zero?
(A)∆H
(B)∆S(Total)
(C)∆S(System)
(D)∆G°
I know that at equilibrium ∆G=0, and was facing difficulty in connecting the above mentioned ...
3
votes
2answers
96 views
How to derive the relation between entropy and heat described by the equation dS=dq/T?
I know that entropy is measure of disorder, and a book (Intro to Thermal Physics by David J. Schroeder) states that $\mathrm dS=\mathrm dq/T$, where $S$ is entropy, $q$ is heat flow, and $T$ is ...
0
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2answers
77 views
Equilibrium chemical potential if the population is not conserved?
The chemical potential, $\mu$, is equal to the free energy $F$, per photon.
$$F = \mu = u-Ts$$
The energy per photon is $u=h\nu$ and $s$ is the entropy per photon. Say we have a process where an ...
4
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1answer
320 views
Isn't the change in Gibbs free energy for a reversible process zero?
In problem 6, part 6.5 of the 2020 IChO (PDF), a thermodynamic cycle is given for “one mole of monoatomic perfect gas”:
$\mathrm{A \to B}$; isothermal reversible expansion receiving $\pu{250 J}$ by ...
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1answer
68 views
Justifying assumptions about method to find equilibrium pressure for co-existence of graphite and diamond
The standard state Gibbs free energies of formation of $\ce{C(graphite)}$ and $\ce{C(diamond)}$ at $T = \pu{298 K}$ are $\pu{0 kJ mol-1}$ and $\pu{2.9 kJ mol-1}$, respectively.
The conversion of ...
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2answers
101 views
What does the change in Gibbs Free Energy refer to?
Usually change is indicated as the difference between some initial and final state. However, for ΔG there seem to be multiple definitions and I am a bit confused. For example, at equilibrium, ΔG = 0 ...
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2answers
53 views
Change in entropy in reversible and irreversible processes
The change in entropy for a reversible process is given as-
$\Delta$S = $\frac{q_{rev}}{T}$
Where qrev is the heat supplied isothermally and reversibly.
The change in entropy for a irreversible ...
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0answers
33 views
Where is my non-expansive work in combustion?
Consider if I burn some octane.
The enthalpy released is $5430 \;\text{kJ/mol}$. The Gibbs free energy released is $5537 \;\text{kJ/mol}$.
From my understanding, enthalpy is the heat change in the ...
5
votes
2answers
234 views
Does entropy contribute work?
I've seen that Gibbs free energy is defined as the maximum amount of work that a system can do. From this I gather, this is how much energy it will release - right?
But, I've also learnt that the heat ...
2
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0answers
49 views
Raising melting point of water at STP (using disolved impurities)
Typically, water experiences melting point depression when it is impure. The more impure it is, the lower the melting point, up to a point.
I understand you could raise the melting point by increasing ...
2
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0answers
68 views
Determining Boiling Point and Melting Point by Graph
This is the plot of $\Delta G^{^\circ}$ vs $T$ for $\ce{Pb-> PbO}$
I understand that the points where there is a sudden change in the slope of the graph, there is a phase change but exactly what ...
3
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0answers
52 views
Is there a parameter for degree of ‘mixedness’
So I was making coffee this morning and when mixing some milk into the black coffee, I wondered if there was some parameter or value in chemistry which describes how well mixed two liquids (or gases) ...
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0answers
24 views
What is 'non-expansion work' and how does ΔG represent the maximum non-expansion work that can be extracted in a reversible process? [duplicate]
I have just learned about Gibbs free energy and how its value indicates the change in entropy of the universe and can thus be used to find the spontaneity of a reaction. However, I found this other ...
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2answers
82 views
Are spontaneous exothermic reactions spontaneous due to more stable products or to an increase in the entropy of the surroundings? [closed]
The lattice formation of an ionic compound from its infinitely separated gaseous ions is spontaneous under standard conditions, but I cannot figure out the 'driving force' behind this.
One way to look ...
2
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0answers
44 views
Entropy change during electrolysis of water
Consider the electrolysis of water reaction:
$$\ce{H_2O -> H_2 + 1/2O_2}$$
At room temperature and atmospheric pressure, the change in enthalpy of this reaction is $\Delta H = \pu{+286 kJ mol-1}$. ...
4
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1answer
88 views
Entropy change and heat transfer in non-ideal heat engines
Please help me, a mathematician, to make sense of entropy. I know it's a topic with about a million questions already, so I understand if this gets ignored. Yet for the life of me, I cannot make sense ...
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1answer
71 views
Are the derivations on Gibbs free energy consistent with the interpretation of entropy?
User Buck Thorn writes here that
In chemistry we are most often interested in the effect of changes in $T$ or $P$ on $\Delta G$ for some process such as a phase change or chemical reaction which is ...
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43 views
Why isn't entropy dimensionless?
The usual units are J/K, however
the only reason temperature has different units than energy is because we didn't used to know temperature was just the average kinetic energy of atoms/molecules. ...
5
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1answer
44 views
Why is the spectroscopic entropy of carbon monooxide higher than that of nitrogen?
While solving a question set, I found a question with this data table (at $\pu{298K}$):
$$
\begin{array}{lrrr}
\hline
\text{Substance} & T_\mathrm b/\pu{K} & S^⦵_\mathrm{cal}/R & S^⦵_\...
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44 views
Calculating specific heat capacity from entropy
I'm currently struggling with a specific thermodynamics problem.
I'm given the entropy of a system (where A is a constant with fitting physical units): $$S(U,V,N)=A(UVN)^{1/3}$$
I'm asked to calculate ...
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1answer
40 views
Why is enthalpy and not heat released by system used while calculating entropy of surroundings?
While finding the sum of change in entropy of the universe and thus defining Gibbs free energy, why is the change in entropy of surrounding the negative of enthalpy of the system divided by the ...
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0answers
23 views
Entropy between elements and compounds
I have encountered this reaction when I am learning entropy:
I don't understand why there is an increase in entropy (said to be slightly larger than 0).
What I am thinking is:
both reactants and ...
2
votes
3answers
450 views
Does the entropy of a chemical system increase in an endothermic reaction?
Since entropy increases when temperature increases, the entropy of surroundings increases during an exothermic reaction. When I apply the same logic, it seems like the entropy of a chemical system ...
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1answer
74 views
Ordered and random energy [closed]
One of the books refer to potential energy being ordered whereas heat energy being random. Could someone explain what is ordered and random energy?
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36 views
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 ...
2
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0answers
37 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 ...
0
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1answer
97 views
Entropy problem [closed]
A tank is divided into two equal chambers by an internal diaphragm. One chamber contains methane at a pressure of $\pu{500 bar}$ and a temperature of $\pu{20 °C},$ and the other chamber is evacuated. ...
4
votes
1answer
71 views
What is the trend in hydration entropy of alkali metal ions?
Is there a trend in alkali metal ion hydration entropy?
There's much talk of hydration enthalpy, but I have a hard time finding information about the change in entropy.
Am I right in thinking that Li$^...
-1
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1answer
72 views
why is entropy maximum at equilibrium for a closed system? [closed]
I don't understand why entropy is maximum at equilibrium for a closed system:(
I tried understanding some of the answers her on chemistry StackExchange but they involved the use of probabilistic ...
3
votes
2answers
49 views
Isobaric entropy relation from isothermal Gibbs free energy relation
I have been given a problem to derive a relation for change in entropy from change in Gibbs free energy:
Starting with the isothermal equation
$$G(p_2) = G(p_1) + nRT\ln\frac{p_2}{p_1}\label{eqn:1}\...
2
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0answers
47 views
Entropy of free expansion and isothermal process
Let me tell what I understand of the concepts on which the question is based first.
Heat is a flow of energy that takes place due to a temperature gradient.
When doing reversible isothermal expansion ...
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2answers
193 views
Total entropy change for a spontaneous reaction
For the oxidation of iron,
$$\ce{4 Fe(s) + 3 H2O(g) -> 2 Fe2O3(s) + 3 H2(g)}$$
the entropy change is $ \pu{–549.4 J K^{-1} mol^{-1}}$ at $\pu{298 K}.$ In spite of the negative entropy change of ...
3
votes
2answers
64 views
How can change in entropy be the same for all processes if the entropy production $\sigma$ is present for irreversible processes?
From the definition of entropy change,
$$S_2-S_1=\left ( \int_{1}^{2} \frac{\delta Q}{T}\right )_{int.rev}$$
From the closed system entropy balance, we have
$$S_2-S_1=\left ( \int_{1}^{2} \frac{\delta ...
3
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1answer
66 views
Derivation and visualization of cell potential dependency on temperature and entropy
Working from the thermodynamic identity
$$\Delta{S} = -\left(\frac{\partial{\Delta{G}}}{\partial{T}}\right)_p,$$
is it allowed to integrate both sides to obtain an expression derived from the Nernst ...
0
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1answer
57 views
Entropy of Dissolution of Hydrocarbons
Here is what I think I know: The entropy of dissolution reactions increases as methylene groups are added (i.e. butanol has higher entropy of dissolution than propanol). Also, acyclic saturated ...
3
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0answers
79 views
How to find the equilibrium constant under non-standard conditions?
Given the following thermodynamic data at $\pu{298 K}:$
$$
\begin{array}{lrrr}
\hline
\text{Compound} & \Delta_\mathrm{f}H^\circ/\pu{kJ mol^-1} & S^\circ/\pu{J K^-1 mol^-1} & C_p^\circ/\pu{...
3
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2answers
536 views
Change in enthalpy and entropy when sugar dissolves in water
We know that dissolution of sugar in water is a spontaneous process.
So, change in Gibbs free energy $(ΔG)$ must be negative for the overall process:
$$ΔG = ΔH - TΔS < 0$$
Hence either the enthalpy ...
1
vote
1answer
167 views
Entropy change during irreversible process
Entropy change is defined as $\Delta S = \int \frac{\delta Q_{rev}}{T} $, where $Q_{rev}$ is heat transferred through a reversible process. I’m a little confused how this works, so I have a couple of ...
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0answers
81 views
Why does entropy increase in reactions that make more molecules?
I used to understand this (more molecules ⇒ more degrees of freedom), but do no longer, because the total number of atoms is conserved, so translational d.o.f. should just be turned into internal d.o....
0
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1answer
51 views
How to calculate ∆rGº from entropy and ∆fGº in different temperatures? [closed]
"The total oxidation of glucose occurs according to the following chemical equation:
C6H12O6 (s) + 6O2 (g) -> 6CO2 (g) + 6H2O (l)
The following table gives us the free energies of standard ...
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1answer
65 views
Change of entropy of a thermal reservoir [closed]
How to calculate/derive the change in entropy of a heat reservoir as function of its internal energy? If the constant temperature of heat reservoir is T, and
$$ S(U_0)=S_0,$$
what is $$ S(U)? $$
3
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0answers
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(Probabilistic) entropy associated with many equally probable microstates
This is a pretty naive question. The probabilistic definition of entropy is (for a mole of particles)
$$-R\sum_i p_i\ln p_i $$ in which $p_i$ is the probability of a given microstate and $\sum p_i =1, ...
2
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0answers
65 views
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 ...
3
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0answers
34 views
Total Entropy of the Atkinson Cycle
I was researching for a question that asked me to find a ratio of temperatures, and I came across this, which would help me greatly:
Since, most of the temperature changes occur during the isochoric (...
2
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1answer
62 views
What is the mechanism of endothermic dissolution?
My real question is in fact "How can dissolution happen if it's endothermic?" However, there
have been many questions regarding this exact topic and the answers about Gibbs free energy
...
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0answers
27 views
What is the fundamental difference between temperature and energy? [duplicate]
We know that temperature is proportional to the average kinetic energy of a system. We also know that temperature is not the same as energy because the temperature is intensive while the temperature ...
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0answers
106 views
Entropy of a van der Waals' gas
I would like to ask how I could derive the entropy change $dS$ for a van der Waals' gas.
I think I would need to use the total differential of entropy and then use the Maxwell relation shown below.
...
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0answers
36 views
Question about reading NIST datasheets & Gibbs energy of reaction
I'm peeping the NIST thermo tables for $\text{H}$ and $\text{H}_2$, and I'm perplexed.
Seems to me that using
$$G=[\Delta H^\circ_f+H-H^\circ(T_r)]-T\cdot S^\circ$$
(well, actually correcting the ...
1
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1answer
92 views
Helmholtz Free Energy Minimization Proof
In the proof that Helmholtz free energy is minimized at equilibrium, we use the fact that $$\mathrm dS_\text{total}=\mathrm dS_\text{system}+\mathrm dS_\text{bath}\geq 0$$
But we also use the fact ...
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1answer
50 views
conceptual doubt on change in entropy [closed]
we have learnt in thermo that delta S is zero in reversible process
Now, when a solid melts reversibly is delta s zero since reversible or positive since the particles are more energetic in liquid ...
