# Questions tagged [entropy]

For questions about the thermodynamical state function entropy, commonly understood as a measure of disorder.

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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 ...
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### 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 ...
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### 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 ...
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### 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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### 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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### 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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### 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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### 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 ...
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### 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 ...
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### 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 ...
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### 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 ...
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### 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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### 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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### 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 ...
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### 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 $\Delta H = \pu{+286 kJ mol-1}$. ...
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### 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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### 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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### 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. ...
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### 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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### 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 ...
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### 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 ...
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### 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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### 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....
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### 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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### 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 $$S(U)?$$
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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 $\sum p_i =1, ... 0answers 65 views ### Why does the plot of volume and temperature have a kink in a second order phase transition? The$(b)$part of the figure shows how thermodynamic variables change in a second order phase transformation. We observe there is a kink in the plot of volume with temperature. Why is that so? The ... 0answers 34 views ### Total Entropy of the Atkinson Cycle I was researching for a question that asked me to find a ratio of temperatures, and I came across this, which would help me greatly: Since, most of the temperature changes occur during the isochoric (... 1answer 62 views ### What is the mechanism of endothermic dissolution? My real question is in fact "How can dissolution happen if it's endothermic?" However, there have been many questions regarding this exact topic and the answers about Gibbs free energy ... 0answers 27 views ### What is the fundamental difference between temperature and energy? [duplicate] We know that temperature is proportional to the average kinetic energy of a system. We also know that temperature is not the same as energy because the temperature is intensive while the temperature ... 0answers 106 views ### Entropy of a van der Waals' gas I would like to ask how I could derive the entropy change$dS$for a van der Waals' gas. I think I would need to use the total differential of entropy and then use the Maxwell relation shown below. ... 0answers 36 views ### Question about reading NIST datasheets & Gibbs energy of reaction I'm peeping the NIST thermo tables for$\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 ...
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 ...