Questions tagged [entropy]

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

Filter by
Sorted by
Tagged with
9
votes
1answer
401 views

Can the idea of entropy be extended to orbitals?

The forward reaction for: $\ce{HF<->H^+ +F^-}$ is entropically favourable; but energetically unfavorable: as there is too much electron density for $\ce{F^-}$ ion to cope up. That's a reason why ...
0
votes
0answers
31 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
vote
1answer
45 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 ...
0
votes
2answers
55 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 ...
-2
votes
1answer
45 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 ...
8
votes
1answer
688 views

Entropy of Activation and Temperature Dependence

I am trying to understand the extrapolation of enthalpy $\Delta H^{\ddagger}$ and entropy of activation $\Delta S^{\ddagger}$ from the Eyring equation. It's typically cast as: $$\ln\left(\frac{k}{T}\...
2
votes
3answers
68 views

entropy calculation in an irreversible process

I found out that if we want to find the entropy change in an irreversible process let's say $\text{state A} \to \text{state B}$ , we find or make an reversible path for the same process and find the ...
7
votes
1answer
173 views

My Misconception of Entropy

It was recently brought to my attention that my understanding of entropy is wonky at best. In my experience, entropy was introduced (superficially at best) during general chemistry/foundations of ...
2
votes
1answer
1k views

Effect of temperature on equilibrium constant in terms of entropy change

This question was asked in the JEE examination of 2017 : [A] option is incorrect since the system is losing heat and hence $$ \Delta S\lt0$$ [B] Lets assume we have an endothermic reaction $$\ce {...
0
votes
1answer
84 views

Change in Entropy and Enthalpy found over a temperature range and asked to compute the change in Gibb's Energy

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 300 ºC ...
6
votes
3answers
8k views

How can a nonspontaneous reaction occur?

$$\frac{-\Delta G}{T}=\Delta S_{universe}$$ (This equation applies under isobaric and isothermal conditions.) I understand that if $\Delta G$ is positive, the reaction is nonspontaneous, and adding ...
2
votes
1answer
814 views

Entropy change upon mixing cold and hot water

A closed, well-insulated container is filled with $\pu{454 g}$ of water at $\pu{94.4 ^\circ C}$. To the hot water, $\pu{200 g}$ of water ice at exactly $\pu{0 ^\circ C}$ is added. The mixture reaches ...
4
votes
1answer
13k views

Entropy and specific heat capacity

I have seen the equation $S(T_2)=S(T_1)+C_p\ln(T_2/T_1)$ where $C_p$ is the molar heat capacity at a constant pressure. I understand that this assumes that the temperature range is sufficiently small ...
2
votes
1answer
64 views

entropy of vaporization vs entropy of fusion

Is the entropy of vaporization greater than entropy of fusion, for elements? And in which case they can be same, if it so happens? I have asked this here because I couldn't find any satisfactory ...
1
vote
1answer
92 views

Adiabatic expansion of gas

If a real gas is adiabatically expanded against constant pressure, then which of the following will definitely increase? Compressibility factor (Z) or Entropy (S) Correct answer: Entropy My answer: ...
0
votes
2answers
45 views

Thermal equilibrium in reversible processes

In whatever resources I have consulted to study reversible thermodynamic processes, a common statement seems to be : The system and surroundings (if the boundary allows) are in mechanical ($P_{sys}=...
1
vote
1answer
53 views

Entropy increase of both system and surroundings [closed]

In "why chemical reactions happen" the author (James Keeler) says that "a process which leads to an increase in the entropy of the system can be ... exothermic." Could someone ...
6
votes
2answers
326 views

Why is the molar entropy of hexane lower than that of butane?

Entropy is dependent on the complexity of the molecule. Due to this, I expected entropy to increase as the complexity of the molecule increased. According to p 918 of Atkins' Physical Chemistry (9th ...
0
votes
1answer
51 views

Extrema in free energy of a solution?

I am a high school student reading about the second law of thermodynamics, and one of the equations given was the free energy change in dilution. $$\Delta G_{\text{dil}} = -RT \log(C_1/C_2)$$ This ...
-1
votes
1answer
49 views

Feasibility of a Reaction [closed]

I understand for a reaction to be feasible, $\Delta$H needs to be negative and $\Delta$S positive. But in terms of Gibbs free Energy Change, without considering kinectic factors, If $\Delta$H is ...
0
votes
1answer
84 views

Sign of change in enthalpy and change in entropy

Why is it wrong to assert that the change in entropy and the change in enthalpy must always have the same sign? What makes me think that they must have the same sign is the fact that every reaction ...
4
votes
1answer
485 views

Why does spontaneity of a reaction depend on temperature?

As we know, $$\Delta G=\Delta H - T\,\Delta S.$$ Both in my textbook and on the internet, it was given that temperature was a determining factor in the spontaneity of a reaction. For example, when $\...
3
votes
1answer
91 views

How does the entropic force arise within the hydrophobic effect?

I know that the hydrophobic effect is usually explained by the entropic effect originating from the disruption of hydrogen bonds between molecules of water and the nonpolar substance. The hydrogen ...
4
votes
1answer
318 views

Infinite Increase in Entropy when Energy added to Absolute Zero

My textbook states the following: If a system were at absolute zero, an additional small amount of heat energy would lead to an infinite increase in entropy. Such a state is impossible. Absolute ...
-1
votes
1answer
50 views

Change in Entropy and Spontaneity [closed]

I was studying thermodynamics and got stuck with some questions. I am pointing them down. I have studied that $\Delta S_{\text{total}}$ accompanied by a spontaneous process is greater than 0. But is ...
1
vote
1answer
81 views

Apparent paradox regarding spontaneity

Consider the following analysis ( rev and irrev respectively refer to a reversible and an irreversible path, between the same initial and final states): $dU_{rev}=dq_{rev}+dw_{rev}$,and,$dU_{irrev}=...
0
votes
0answers
40 views

How to find entropy of chemical network reaction?

I have the following system of reactions: $$ \begin{aligned} \ce{X_1 + Y_1 &<=>[$k_{21}$][$k_{12}$] X_2} \\ \ce{X_2 &<=>[$k_{32}$][$k_{23}$] X_3} \\ \ce{X_3 &<=&...
0
votes
1answer
37 views

Is entropy of surroundings a state function?

It is a pretty common well known fact that the entropy of a system is a state function ie. it doesn't depend upon the path taken by the process as long as the initial and final states are the same. I ...
3
votes
1answer
75 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 ...
1
vote
1answer
51 views

Is constant pressure heat capacity = entropy during adiabatic reversible expansion of perfect gas?

For any process, ∆G = ∆H - ∆(TS). Apply this on reversible adiabatic expansion of perfect gas, since the entropy of system does not change during this process, S is constant so ∆G = ∆H - S∆T The ...
4
votes
0answers
51 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
vote
1answer
78 views

A Curious (definitely wrong) result of Absolute Entropy [closed]

The Gibbs free energy is defined as $$G=H-TS$$ Differentiating both sides $$dG=dH-TdS-SdT$$ For an adiabatic reversible expansion of an ideal gas, we would have $dG=0$, and $dS=0$. Thus we can write, $...
4
votes
2answers
422 views

What is the entropy of mixing a gas into the whole atmosphere?

Suppose I release 1 mole of pure argon into the atmosphere. What is the entropy of mixing? The equations I have found seem to only apply to the case of a fixed volume. Should I use an estimate of the ...
5
votes
5answers
577 views

Gibbs Free Energy and Entropy

I understand Enthalpy, the exchange of energy between products and reactants. But what is Gibbs Free Energy and Entropy? I know that Gibbs free Energy is the difference between the change in Enthalpy -...
2
votes
0answers
116 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 ...
14
votes
2answers
13k views

Why does like dissolve like?

Polar solvents love polar solutes to be dissolved in it and non polar with non polar. Often said as like dissolves like. Okay, polar loving polar can be understood with help of the facts: same polar ...
7
votes
5answers
798 views

Dependence of change in entropy on temperature

The thermodynamic definition of entropy is expressed as $$dS = \frac{dq_{rev}}{T}$$ I understand that it depends on amount of heat transferred because heat transfer can be understood as the degree of ...
1
vote
1answer
65 views

Are phase transitions reversible when performed at supercooled temperatures?

For the state transition of supercooled water to ice, is the process reversible? I wonder this because I want to know if I can use entropy change of the universe is 0. If it isn't reversible, how do ...
0
votes
0answers
61 views

Why doesn't Delta S total = 0 for this reversible process?

My textbook (Engel Physical Chemistry 3rd Edition) says: For any irreversible process in an isolated system, there is a unique direction of spontaneous change: $\Delta S > 0$ for the spontaneous ...
10
votes
3answers
776 views

Why do the first and second laws of thermodynamics not contradict each other?

We're learning about entropy right now in general chemistry, and I'm trying to understand something. From the fact that entropy can be directly compared with enthalpy, free energy, electromotive ...
0
votes
1answer
57 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 ...
2
votes
2answers
130 views

Entropy and Equilibrium Constant: Chemical Thermodynamics

For a reaction taking place in a container in equilibrium with its surroundings, the effect of temperature on its equilibrium constant $K$ in terms of change in entropy is described by: (A) With the ...
4
votes
2answers
75 views

Why do things want to lower their energy? [closed]

Like if we consider a container of gas molecules as a system, Why does it want to lower its energy? I have read that always more spontaneous events are favored. So Gibb's Free energy should have a ...
3
votes
1answer
58 views

Assumption behind Gibbs energy and maximum work

I'm somewhat confused by this derivation (in Schroeder's Book of Thermal Physics) of the fact that in a closed system, the change in the Gibbs Energy is always less than the Non-Expansion work done on ...
3
votes
1answer
2k views

Relation between equilibrium constant and entropy change

Like the Van't Hoff equation, which relates change in enthalpy to equilibrium constant, is there a similar equation for the relation between change in entropy and equilibrium constant? Consider the ...
4
votes
1answer
363 views

Why is the Standard Entropy of a Proton Zero?

It was my assumption that the standard entropy was the absolute entropy of a substance at standard state; however, my textbook states various standard entropies ranging from $-144.77\ \mathrm{J/(mol\ ...
0
votes
1answer
212 views

Entropy of Irreversible Isothermal Compression

If I want to find the entropy change of universe in isothermal irreversible compression, I use 2 approaches: I use q/T. Which gives me positive entropy change for surroundings positive and negative ...
0
votes
2answers
55 views

T∆S implies that heat flows which way?

From Schroeder's Introduction to Thermal Physics. Parts $(a)$ and $(b)$ are quite simple, and we find that $ \Delta H =-2808\ \mathrm{kJ}$ and $\Delta G =-2879\ \mathrm{kJ}$, so by $\Delta G = \Delta ...
4
votes
3answers
430 views

Relationship between the ideal gas constant and entropy

So it dawned on me the other day that the ideal gas constant $$R = \pu{8.31 J mol-1 K-1}$$ has the same units as molar entropy. Is there some deeper meaning behind this or is it just a coincidence ...
4
votes
2answers
19k views

Calculating Enthalpy Changes at Different Temperatures

To calculate $\Delta H$, the change in enthalpy at $\mathrm{100^\circ C}$ for the reaction below, one needs what addition information? $$\ce{N2(g) + 3H2(g) -> 2NH3(g)}$$ $\Delta H^\circ = ...

1
2 3 4 5 6