Questions tagged [entropy]

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

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What is an example of an exothermic reaction with negative ∆S?

In high school we learn that when a reaction has both negative $\Delta{}S$ (entropy change) and negative $\Delta{}H$ (enthalpy change) it occurs spontaneously at lower temperatures, but becomes non-...
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1answer
97 views

Why is the Gibbs free energy of a reversible reaction not always 0? [duplicate]

From my understanding, reversible proceses are those where the expression: $$\Delta S_\mathrm{total} = \Delta S_\mathrm{system} + \Delta S_\mathrm{surroundings} = 0$$ is true for all for the entire ...
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2answers
242 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 ...
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1answer
201 views

How to compute change in Gibbs energy given change in entropy and enthalpy found over a temperature range?

I was given the following question by my tutor: The variation of enthalpy ($\Delta H$) and entropy ($\Delta S$) in a reaction carried out at constant pressure in the temperature range between $\pu{...
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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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1answer
336 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
78 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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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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201 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 ...
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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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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 wrong in this argument that dG must always be zero?

Under constant temperature and pressure, the change of the Gibbs free energy can be written as $$\mathrm dG_\textrm{sys} = \mathrm dH_\mathrm{sys} - T\,\mathrm dS_\mathrm{sys}$$ And in the textbook ...
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2answers
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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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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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Entropy of surroundings and heat

Apparently the entropy change of a system can be found by $$\mathrm dS=\frac{\mathrm\delta q_\mathrm{rev}}T$$ I am slightly confused about this because I have seen this being used when the temperature ...
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0answers
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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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688 views

The spontaneity of a redox reaction

Suppose we have a redox reaction and we want to see in what direction the reaction is spontaneous. We do this by comparing the standard reduction potentials of the sub-reactions available in the main ...
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1answer
416 views

What's the minimum amount of energy needed to remove CO2 from the atmosphere?

I've been learning about CDR (Carbon Dioxide Removal) techniques to combat climate change. These all seem to involve extracting $\ce{CO2}$ from the atmosphere and converting to a mineral, which is ...
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1answer
89 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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Entropy increase when heating a gas

What is the entropy change when the temperature of 1.00 mol of ideal gas is raised reversibly from 10 °C to 50 °C at constant pressure, constant volume, and assuming the heat capacity is independent ...
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1answer
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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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2answers
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How to calculate what temperature change in entropy for the reaction equal to the change in entropy for the surroundings given Enthalpy and entropy

A reaction has $\Delta H_\textrm{rxn} = \pu{-107 kJ}$ and $\Delta S_\textrm{rxn} = \pu{285 J/K}$. At what temperature is the change in entropy for the reaction equal to the change in entropy for the ...
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544 views

Entropy change of surroundings and system

The entropy change of the surroundings can be calculated by the equation $dS_{sur}=\frac{dq}{T_{sur}}$ regardless of the path (irreversible or reversible). The argument is that because the ...
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0answers
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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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1answer
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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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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
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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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Where to find data for Gibbs energy, enthalpy, and entropy?

Where can you find the enthalpy and Gibbs free energy of formation and entropy of compounds either as a data file or web API? Technically, I only need two since I can figure out the other one from two ...
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3answers
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What is the relationship between entropy and heat capacity?

The molar heat capacity of hydrogen gas and deuterium gas are nearly the same, $\pu{28.8 J K-1 mol-1}$ and $\pu{29.2 J K-1 mol-1}$, respectively, but the absolute entropy of deuterium ($\pu{145.0 J K-...
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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 ...
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1answer
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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 ...
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1answer
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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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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{...
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3answers
551 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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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 ...
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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 ...
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Whats the difference between entropy and the (dis)order of a system?

Entropy is often verbally described as the order/disorder of the thermodynamic system. However, I've been told that this description is a vague "hand-waving" attempt at describing what entropy is. For ...
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2answers
79 views

How can you calculate the tendency of one compound to become another?

Excuse my inexperience with chemistry here. I've been poring over papers with terms like "Standard Gibbs free energy of formation", "Hess's Law", "standard enthalpy of ...
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1answer
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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. ...
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2answers
602 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 ...
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1answer
75 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$^...
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1answer
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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 ...
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4answers
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Can one predict the entropy change for aqueous phase reactions without calculation?

I have seen several sources that claim aqueous solutions always have more entropy than pure liquids or solids, however, some aqueous ions have negative standard entropy. This opens the possibility of ...
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2answers
51 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}\...
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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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