Skip to main content

Questions tagged [entropy]

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

62 questions with no upvoted or accepted answers
Filter by
Sorted by
Tagged with
7 votes
0 answers
181 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....
Furrier Transform's user avatar
5 votes
0 answers
112 views

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 ...
MackTuesday's user avatar
5 votes
1 answer
966 views

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 ...
Nanoputian's user avatar
  • 7,412
4 votes
2 answers
1k 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 $\Delta H = \pu{+286 kJ mol-1}$. ...
SalahTheGoat's user avatar
4 votes
0 answers
85 views

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 ...
1__'s user avatar
  • 696
4 votes
0 answers
561 views

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. ...
Tips's user avatar
  • 209
4 votes
0 answers
403 views

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 ...
Aditya Shrivastava's user avatar
3 votes
0 answers
88 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) ...
arevmelikyan's user avatar
3 votes
0 answers
117 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{...
user avatar
3 votes
0 answers
47 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 (...
8packgrandma's user avatar
3 votes
0 answers
43 views

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 ...
user avatar
3 votes
0 answers
777 views

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 ...
Secret's user avatar
  • 698
3 votes
0 answers
449 views

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/...
Jess L's user avatar
  • 302
3 votes
0 answers
950 views

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 ...
Nanoputian's user avatar
  • 7,412
2 votes
1 answer
64 views

Entropy and Internal Energy in irreversible adiabatic process

I have a question related to title. Please see the following discussion: In an irreversible process: $ΔU_\mathrm{irr} = q_\mathrm{irr} + w_\mathrm{irr}$ $ΔU_\mathrm{rev} = q_\mathrm{rev} + w_\mathrm{...
user146901's user avatar
2 votes
0 answers
60 views

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 ...
hyportnex's user avatar
  • 557
2 votes
0 answers
153 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 ...
EdL's user avatar
  • 157
2 votes
0 answers
372 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 ...
UNAN's user avatar
  • 143
2 votes
0 answers
119 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 ...
Aseem Mittal's user avatar
2 votes
0 answers
43 views

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 ...
R Dev's user avatar
  • 313
2 votes
0 answers
360 views

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 ...
George Tian's user avatar
  • 1,371
2 votes
0 answers
175 views

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 ...
Joe 's user avatar
  • 35
2 votes
0 answers
69 views

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{...
user3256725's user avatar
2 votes
0 answers
601 views

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 ...
carbenoid's user avatar
  • 2,042
2 votes
0 answers
123 views

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 ...
user11629's user avatar
  • 972
2 votes
1 answer
186 views

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. ...
Aniruddha Deb's user avatar
1 vote
0 answers
59 views

Work from a spontaneous endothermic reaction?

Some reactions are spontaneous ($\Delta_\mathrm{r}G < 0$) although they are endothermic ($\Delta_\mathrm{r}H > 0$), e.g. the plastic packs that once cracked they get cold. I saw that it is often ...
Olfaction's user avatar
1 vote
0 answers
53 views

Temperature dependence on the feasibility of an equilibrium

If we consider a reaction A + B ⟶ C + D, with $\Delta$S $>0$, then regardless of whether $\Delta$H is positive or negative, increasing the temperature will make $\Delta$H - T$\Delta$S more negative,...
Ariichu's user avatar
  • 21
1 vote
0 answers
52 views

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 ...
tgsweat's user avatar
  • 23
1 vote
0 answers
64 views

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 ...
C-Consciousness's user avatar
1 vote
0 answers
119 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. ...
Mikayla Eckel Cifrese's user avatar
1 vote
0 answers
205 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 ...
SphericalApproximator's user avatar
1 vote
0 answers
292 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 ...
Question's user avatar
  • 355
1 vote
0 answers
457 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. ...
Felix Yeung's user avatar
1 vote
0 answers
143 views

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 ...
Martha Salman's user avatar
1 vote
0 answers
234 views

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 ...
Schwarz Kugelblitz's user avatar
1 vote
0 answers
44 views

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 ...
sweetandtangy's user avatar
1 vote
0 answers
939 views

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_\...
user8081591's user avatar
1 vote
0 answers
89 views

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 ...
thepith's user avatar
  • 21
1 vote
0 answers
1k views

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 ...
KeatonB's user avatar
  • 630
1 vote
0 answers
977 views

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 ...
Mathematician's user avatar
1 vote
0 answers
86 views

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 ...
Julys Pablo's user avatar
1 vote
0 answers
207 views

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 ...
JustSomeBoy's user avatar
1 vote
0 answers
2k views

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 ...
carbenoid's user avatar
  • 2,042
1 vote
0 answers
1k views

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\ \...
RobChem's user avatar
  • 9,804
0 votes
0 answers
23 views

Reaction entropies of lithium-ion electrodes

I'm looking for lithium-ion electrode materials with good thermogalvanic properties for heat harvesting. As a sort of pre-screening effort, I am looking for information about the entropy change of ...
wawas007's user avatar
0 votes
0 answers
44 views

Why does enthalpy change and not internal energy help in determination of spontaneity?

Spontaneity of a process is measured by Gibbs Free Energy $$\Delta G= \Delta H-T\Delta S$$ $$\Delta H=\Delta U+\Delta (PV)$$ Is there an intuitive explanation for why Gibb's energy depends upon ...
Portuguese Man Of War's user avatar
0 votes
0 answers
45 views

Justifying that Standard Entropy of a Reaction is a Constant of Temperature

One of the parts in a question I'm trying to solve for an assignment goes like this: A key issue in the Hydrogen Economy is Hydrogen Storage. This can be restored if a substance $X$ can bind to $H_2$....
poirot_06's user avatar
0 votes
0 answers
129 views

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 ...
Natasha J's user avatar
  • 273
0 votes
0 answers
56 views

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{...
Sagnik's user avatar
  • 13