Questions tagged [entropy]
For questions about the thermodynamical state function entropy, commonly understood as a measure of disorder.
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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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Describing evaporation without entropy -- what about Helmholtz?
I have in mind a rigid, impervious, heat-insulating vessel containing a monatomic liquid and vacuum. The vessel has an insulating forcefield inside, exactly at the surface of the liquid. It can be ...
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Entropy Change of Resistor
A very large swimming pool filled with water of temperature equal to $20\ \mathrm{^\circ C}$ is heated
by a resistor with a heating power of $500\ \mathrm{W}$ for $20$ minutes. Assuming the water in ...
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Is entropy maximum in equilibrium?
Usually, in the context of non-equilibrium thermodynamics, it is said that entropy achieves a maximum in equilibrium, so the Taylor series expansion of entropy around the equilibrium state as a ...
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Whether the entropy change of the system is positive or negative
$$\ce{N2(g) + O2(g) → 2NO(g)}$$
My thinking: since gases are combined together, so there randomness or disorder gets decreased. Hence the sign of entropy change of the system should be negative.
...
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Precise explanation of macrocyclic effect
In most of the books, the reason of macrocyclic effect is given that It occurs due to preorganised structure of macro-cyclic ligand.
But a proper explanation of these two particular examples isn't ...
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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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How to find the equilibrium constant under non-standard conditions?
Given the following thermodynamic data at $\pu{298 K}:$
$$
\begin{array}{lrrr}
\hline
\text{Compound} & \Delta_\mathrm{f}H^\circ/\pu{kJ mol^-1} & S^\circ/\pu{J K^-1 mol^-1} & C_p^\circ/\pu{...
user85551
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(Probabilistic) entropy associated with many equally probable microstates
This is a pretty naive question. The probabilistic definition of entropy is (for a mole of particles)
$$-R\sum_i p_i\ln p_i $$ in which $p_i$ is the probability of a given microstate and $\sum p_i =1, ...
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Total Entropy of the Atkinson Cycle
I was researching for a question that asked me to find a ratio of temperatures, and I came across this, which would help me greatly:
Since, most of the temperature changes occur during the isochoric (...
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Discussion about Warren-Cowely Parameter
The Warren-Cowely Parameter (WCP) for short range solution order is defined as:
$$\mathrm{WCP}_{ij} = 1 - \frac{Z_{ij}}{x_j \cdot Z_i}$$
where $Z_{ij}$ is the partial Coordination Number (CN) of ...
user89031
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Example of an endothermic reaction that can sustain itself for at least an hour?
Recall that in physical chemistry, the spontaneity of a reaction at constant pressure and a given temperature $T$ can be quantified by the Gibbs free energy
$$\Delta G = \Delta H - T \Delta S$$
A ...
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Thermodynamics: Solving for Entropy, Gibbs and Helmholtz
A reversible melting of $32.0\ \mathrm g$ of ice at $0\ \mathrm{^\circ C}$ and $1\ \mathrm{atm}$. Solve for $\Delta G, \Delta S_\text{universe}$, and $\Delta A$
I'm also given latent heat of fusion/...
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Determining pressure of sublimation of iodine
The pressure of sublimation of iodine can theoretically be determined by considering the two hypothetical steps: the sublimation of iodine at $\pu{298 K}$, followed by an isothermal expansion of our ...
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Prigogine vs. Bronsted and the minimum entropy production principle
I apologize for the length of this question that was asked here prigogine-bronsted but got no reply; anyhow, Bronsted's name is much better known among chemists than among physicists...
Prigogine's ...
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Raising melting point of water at STP (using disolved impurities)
Typically, water experiences melting point depression when it is impure. The more impure it is, the lower the melting point, up to a point.
I understand you could raise the melting point by increasing ...
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Determining Boiling Point and Melting Point by Graph
This is the plot of $\Delta G^{^\circ}$ vs $T$ for $\ce{Pb-> PbO}$
I understand that the points where there is a sudden change in the slope of the graph, there is a phase change but exactly what ...
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Entropy change during electrolysis of water
Consider the electrolysis of water reaction:
$$\ce{H_2O -> H_2 + 1/2O_2}$$
At room temperature and atmospheric pressure, the change in enthalpy of this reaction is $\Delta H = \pu{+286 kJ mol-1}$. ...
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Entropy of free expansion and isothermal process
Let me tell what I understand of the concepts on which the question is based first.
Heat is a flow of energy that takes place due to a temperature gradient.
When doing reversible isothermal expansion ...
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Why does the plot of volume and temperature have a kink in a second order phase transition?
The $(b)$ part of the figure shows how thermodynamic variables change in a second order phase transformation.
We observe there is a kink in the plot of volume with temperature.
Why is that so?
The ...
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Estimation of Molar Entropies
There are plenty of compounds out there with unknown standard molar entropies. I know that molar entropy has a strong dependance on the physical phase, molecular weight, and number of atoms. So is it ...
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How to compare standard entropy of diatomic gases?
Say, for example, I wanted to compare the standard entropies of $\ce{Cl2(g)}$ and $\ce{F2(g)}$. They both are equimolar.
I understand that entropy is a measure of how many states a particle can ...
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Change in enthalpy and entropy for the formation of nickel tetracarbonyl
I was working on an enthalpy/entropy problem and I had a question on predicting the signs of some reactions. For the reaction
$$\ce{Ni (s) + 4 CO (g) -> Ni(CO)4 (g)}$$
my textbooks says that ...
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Why do some chemical reactions lead to less stable state?
If the universe is always trying to find a more stable energy state, then how do reactions take place that lead to a less stable state e.g. the formation of ammonia from extremely stable diatomic $\ce{...
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Meaning of negative entropy value
I was looking through the thermodynamic data chart at the back of my textbook and found that $\ce{S^{2-}_{(aq)}, F^{-}_{(aq)}, OH^{-}_{(aq)}}$ all have negative entropy values. But according to the ...
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In entropy change of surroundings, what is T?
This question is simpler than the previous one about intuition of entropy; I just need to know whether the $T$ term in $dS_{Surr} = \frac{-dH}{T}$ refers to the temperature of the surroundings or the ...
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Density of water increases from 273 to 277 K due to increase in entropy?
In a set of questions that I was solving, the answer to one of the questions asking why the density of liquid water increases from 0 to 4 degrees C had the above answer: due to an increase in entropy. ...
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Is there an equivalent term for favourable and non-favourable entropy?
For Gibbs energy, we have 'exergonic' or 'endergonic'
For Enthalpy, we have 'exothermic' or 'endothermic'
It seems logical there should be an equivalent pair of terms for entropy, but I can't seem to ...
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Can reverse micelle's exist outside solution?
As in reverse micelle's, the polar liquid remains inside the micelle while the exterior is one of lower dielectric constant; if the liquid were to be carefully removed, would the micelle structure ...
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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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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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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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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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Thermochemical data for thiocyanatoiron(III) ion
I am currently writing a lab report about the formation constant of $\ce{FeSCN^2+}.$ All I could find online was a formation constant at $\pu{25 °C}$ $(890),$ which was 70% higher than the ...
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Entropy in organic chemistry
Why do we not talk about entropy when deciding feasibility of an organic reaction?...We always seem to only be interested in stability of product and intermediate(essentially delta H)and draw their ...
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What makes determining entropy changes theoretically so hard compared to enthalpy?
It is really hard to determine the entropy change of a reaction accurately because of subtle solvent effects and a lack of standard entropies. On the other hand, enthalpy is relatively easy and ...
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Molar entropy of vaporization
If a substance has a molar heat of vaporization of $\pu{3.05\times10^4J/mol}$ and a normal boiling temperature of $\pu{80.0^\circ C}$, what is the value of its molar entropy of vaporization $\Delta S_\...
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Change in Free Energy in Gas Reaction
I try to estimate whether particles form pairs or not.
What I know is the difference in the potential Energy $\Delta U_\mathrm{pot}$ which occurs when both particles form a pair.
When I have a ...
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Mechanism for Hydrogen Peroxide decomposition?
Someone asked this question earlier and made no attempt at understanding it on their own so the question was flagged. However, it prompted me to attempt to figure it out. This is what I have come up ...
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Why do reactions reach equilibrium?
If the forward reaction causes an increase in entropy then the backwards reaction causes a decrease in entropy, so the backwards reaction is non-spontaneous. If so, then why does the backwards ...
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Entropy as "extent of energy dispersal" vs. entropy as defined by the Clausius equation
Currently, the concept of entropy as "energy dispersal" has been proved to be more easy to understand than the concept of "disorder". While the first can be applied successfully to explain the ...
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Energy required to break salt bridges in peptides and proteins
Is there a way to calculate the energy required to break a salt bridge in a peptide or on the exposed surface of a protein in aqueous solution? Is there any useful literature on this topic? I'm ...
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Entropy change of surroundings
The entropy change of a system is given by
$$\mathrm dS=\frac{\mathrm dq_\text{rev}}{T}$$
which at constant temperature is
$$\Delta S=\frac{q_\text{rev}}{T}$$
I also learned that the entropy change ...
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Entropy change when liquids at two different temperatures are mixed
Two quantities of water ($M_\mathrm{r}=18$) each of mass $216\ \mathrm{g}$ are mixed together in a
vessel. The temperatures of the two quantities before mixing are $303\ \mathrm{K}$ and $333\ \...
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Reversible path for Entropy change on crystallisation
I am trying to re-learn thermodynamics but have come stuck with this question so am seeking help.
Two moles of supercooled water at $265$ K freeze to give ice at the same temperature. Using $\Delta ...
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Thermochemical parameters at high temperature
I wanted to calculate Thermodynamic parameters such as Gibbs Free energy, Enthalpy change and Entropy change using Curtis et al explained as this link: https://gaussian.com/wp-content/uploads/dl/...
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Why is work done on the system in irreversible adiabatic compression greater than work done on the system in reversible adiabatic compression?
So, while reading about Quasi- Static process, I came across this question here:
Question about Quasi- static process
From the answers given there, what I understood is this: After irreversible ...
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Determine enthalpy and entropy from measurements of Kd at different temperatures?
In biochemical experiments, it is very common to measure IC50 (half inhibitory concentration) eg by adding different amounts of an inhibitor to an enzyme+substrate and measuring the reaction rate or ...
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Use the first law of thermodynamics to derive the pressure as a function of T, U, V and N
I am struggling with a thermodynamics question given
$$S(U,V,N)=C_VNK_\mathrm b\ln U/U_0+NK_\mathrm b\ln V/V_0$$ (where $U_0$ and $V_0$ are the reference energies and volumes) and the first law of ...
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Effect of degree of freedom on entropy change during a reaction
In the reaction $$\ce{C_{(s)} + O2_{(g)} -> CO2_{(g)}} $$
one mole gaseous reactant gives one mole gaseous product, so there is no significant change in entropy. It can be verified by line of $\ce{...
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