Questions tagged [entropy]

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

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20
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2answers
6k views

Formula of entropy change

In my 12th standard book, the formula for entropy change is given as $\Delta S = \frac{q_\text{reversible}}{T}$. What is the importance of absorbing heat reversibly and not irreversibly? What does ...
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On adding sugar to water, does the entropy increase or decrease?

This question is a little confusing. According to my teacher, the entropy should decrease, but I think that sugar is crystalline first and later it dissolves, so the randomness increases and so the ...
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575 views

Why can't a reaction go to completion?

What is the reason for why an exergonic reaction would still have some remaining reactants (or an endergonic reaction to have any products)? The explanation given on this page (see Chemical reactions ...
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3answers
415 views

Entropy - “Wiggle”?

The title is not a reference to a Jason Derulo song. In any case: 1) How is change in entropy measured, experimentally? I've Googled this for a bit and I've found all sorts of mathematical ...
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2answers
1k views

Does deuterated water slow down the overall metabolism of a cell?

Would deuterated water, being heavier, slow down the metabolic rate of the cell and subsequently the aging process? edit: lets say I wanted to observe a cellular event, like the formation of the ...
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2answers
12k 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 ...
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3answers
695 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 ...
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2answers
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Can someone intuitively explain the reason for the units of entropy (J/K )? [duplicate]

If entropy is just a measure of the "randomness" or "chaos" of a system, then why does it have specific units. What is the reason behind the units of entropy being J/K?
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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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4answers
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Why is entropy favorable?

I cannot seem to grasp the logic behind it. We say that more entropy (or more disordered system) is favorable over less entropy. But why? Why is randomness preferred over proper arrangement of atoms/...
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3answers
12k views

What does the Clausius Inequality mean in thermodynamics? (entropy)

$$\delta S\ge\frac{\delta q}T$$ I don't understand how a quantity (the change in entropy in this case) can be greater than the very thing that defines it ($\mathrm{\frac{\delta q}{T}}$). Also what ...
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2answers
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What kind of chemicals would exist at the heat death of the universe?

As the universe reaches the maximum entropy, presumably only the most stable chemicals would exist. Assume that all the elements haven't turn into iron yet, what kind of chemicals would dominate at ...
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Entropy change in an adiabatic expansion

Question One mole of ideal gas initially at a pressure of 1 atmosphere and $T = 298\ \mathrm K$, is expanded into a volume 50 % larger adiabatically. In this adiabatic process, no work is done on ...
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1answer
400 views

deltaS of a decomposition reaction

Suppose we had the following reaction: $$\ce{Polymer ($n$~units)_{(aq)} -> Polymer($a$~units)_{(aq)} + Polymer($n-a$~ units)_{(aq)}}$$ Without knowing the specific monomer unit of the polymer, ...
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4answers
10k views

When is a reaction reversible?

When speaking in thermodynamic terms, when is a reaction reversible? My attempt: A reaction is reversible when $\Delta\text{S} < 0$, because according to the second law of thermodynamics, "in ...
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3answers
633 views

Why does everything go in the direction of positive entropy change?

I read about entropy from different sources. Still don’t get why (universal) entropy change has to be greater than zero for irreversible process, i.e. $\mathrm{d}S_\mathrm{Univ}>0$. Is it a result ...
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1answer
639 views

What Causes there to be a Maximum Amount of Salt which can be Dissolved in Water?

When you add salt to water and stir, after a while the salt will no longer dissolve. Why is this?
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15k views

What is the difference between ΔG and ΔG “with an o on top”? [duplicate]

What is the difference between $\Delta G$ and $\Delta G^\circ$? I couldn't figure it out. Ex: $\Delta G^\circ = -RT\ln K$ $\Delta G = \Delta G^\circ + RT \ln Q$ What is the difference, is it that $\...
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1answer
4k views

Spontaneity of an exothermic reaction when temperature is decreased

How is the spontaneity of an exothermic reaction changed when temperature is decreased? Assuming the entropy is negative. Using Gibbs free energy equation, $\Delta G=\Delta H-T\Delta S$, $\Delta G$ ...
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0answers
674 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}\...
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3answers
6k views

Where to find data for gibbs energy, enthalpy, and entropy digitally

Where can you find the enthalpy and gibbs free energy of formation and entropy of compounds either as a data file or web api (I technically only need two since I can figure out the other one from two ...
7
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1answer
365 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 ...
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3answers
7k views

Is there a way to experimentally measure entropy?

I've been doing thermodynamic chemistry, and recently focusing on Gibbs Free Energy. Whilst doing calculations using, $$\Delta G = \Delta H - T \Delta S$$ I have been given a table of values for $\...
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1answer
706 views

Misconception? “That gas is heavier so it sinks.”

I've heard people say many times that one gas is heavier than the other so the heavier gas sinks. Now this must certainly be true to a certain extent (I think of gas used in WWI that sunk into ...
7
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1answer
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How can enthalpy change of a system be negative while entropy change is positive?

$$\Delta G = \Delta H_\text{system}-T\Delta S_\text{system}$$ $$ \begin{array}{ccc} \hline \text{Sign of}~ΔH & \text{Sign of}~ΔS & \text{Spontaneity} \\ \hline + & + & \text{The ...
7
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1answer
692 views

Why does increasing the temperature of a *solid* increase its entropy?

I understand why increasing the temperature of a fluid would increase its entropy, as the particles are free to move, and therefore an increase in kinetic energy would allow the particles to move more,...
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5answers
669 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 ...
7
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2answers
203 views

Feasibility and Entropy

Suppose you've got some reaction that has a positive $\Delta H$, and also has positive $\Delta S_\mathrm{sys}$. Due to the equation $$\Delta S_\mathrm{tot} = \Delta S_\mathrm{sys} - \frac{\Delta H}{T}$...
7
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1answer
165 views

What is the precise definition of standard molar entropy?

I understand what the standard molar entropy is, and how to use it in calculations, but I'm interested in understanding exactly how it's defined and measured. My recollection from a long time ago is ...
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2answers
7k views

How to calculate the entropy change of benzene when it changes from vapour into liquid?

Given information: The boiling point of benzene at atmospheric pressure is $353~\mathrm{K}$ the enthalpy of vaporization of benzene is $30.8~\mathrm{kJ~mol^{−1}}$ at this temperature. ...
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0answers
346 views

Is helium-4 a liquid at zero temperature and zero pressure?

As far as I know, for all substances other than helium, if you extrapolate the solid-gas line on the phase diagram, it passes through the origin. That is, no matter how low the temperature is, you can ...
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4answers
3k views

Why does entropy increase when the difference in temperatures is decreased?

In irreversible heat transfer, heat energy is irreversibly transferred from the higher temperature system to the lower temperature system, and the combined entropy of the systems increases. Source: ...
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2answers
1k views

Na(s) vs NaCl(s) Entropy

I would think the crystalline, ionic solid would have the lower entropy, however, the tablature indicates otherwise. Why does $\ce{NaCl(s)}$ have a greater entropy than $\ce{Na(s)}$?
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3answers
406 views

Trying to Understand Entropy

I'm currently looking at Principles of Chemistry by Atkins, and I have a few questions involving entropy. These questions probably arise from my poor understanding of reversible/irreversible processes....
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1answer
1k views

Derive expression for internal energy of mixing and entropy of mixing using statistical thermodynamics

I want to derive an expression for the internal energy of mixing, $\Delta_\mathrm{mix}U$, and entropy of mixing, $\Delta_\mathrm{mix}S$. The framework for this is the Lattice Theory of Ideal Solutions....
6
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1answer
490 views

Entropy change when indistinguishable particles suddenly become distinguishable

We have that $$ S = \frac{U}{T} + k\ln Q $$ Using that for indistinguishable particles in the canonical ensemble $$ \ln Q_{\mathrm{indis}} = N\ln \frac{q_{\mathrm{tr}}e}{N} + N\ln q_{\mathrm{rot}} ...
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2answers
323 views

Calculating Entropy

Atkin's Physical Chemistry Book; Chapter 3; question 3.3(a): Question Calculate $\Delta S$ when the state of $\mathrm{3~mol}$ of perfect gas atoms, for which $C_{p,m}$ = $\frac{5}{2}R$, is changed ...
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1answer
1k views

What is an entropic trap?

Can someone explain the concept of entropic traps, or provide good sources to look up? The term is not present in any chemistry books I own, and I cannot find online sources explaining it.
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1answer
2k views

What is the proper term for lines of constant volume and constant enthalpy on a thermodynamic diagram?

I know an isotherm is a line of constant temperature. Isobar is a constant pressure line. Isentrope is a line of constant entropy. But what do you call a line of constant volume? An Isochore? And ...
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2answers
519 views

Thermodynamics: Relation between different types of energy: My Analogy

I have always been confused between the different kind of energies in thermodynamics so today I thought of finally getting it right. Here's my analogy(which is wrong and I need help in improving it, ...
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2answers
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 ...
6
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1answer
107 views

Biomolecular energy functions and entropy

From what I've been reading, it seems that entropy (rather than enthalpy) is the biggest driver of protein folding (especially the burying of hydrophobic residues). However, popular energy functions ...
6
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1answer
309 views

Calculation of the enthalpy change of reactions

First, I’m a high school student and I wonder why every textbook just tells you how to set up those equations and cancel them to get the entropy change but never tells you why you can cancel the same ...
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3answers
3k views

Does a messier room actually have higher entropy?

When my chemistry teacher was explaining entropy, she used the analogy of a clean vs. messy room. What I'm wondering is whether a messy room really does have higher entropy. Does this still work on a ...
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3answers
721 views

Why are protein hydrophobic cores denatured by heat when entropic forces should be favoured at high temperature

The hydrophobic interaction is thought to be driven by an entropic force. If it is, shouldn't hydrophobic interactions be stronger at higher temperatures, where states of higher entropy are favoured? ...
5
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1answer
528 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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2answers
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Entropy of surroundings and heat

Apparently the entropy change of a system can be found by $dS=\frac{\delta q_{rev}}{T}$ I am slightly confused about this because I have seen this being used when the temperature of the system and ...
5
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5answers
569 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 -...
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2answers
52k views

What does negative delta S imply?

What does it mean when there is a negative delta $S$ $(-\Delta S)$? One person asked if this implied negative entropy, but I don't see how this could be possible. Does this imply a negative change in ...
5
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3answers
501 views

What value of temperature does T represent in Gibbs Free Energy Equation?

Temperature before, or after reaction? Temperature change? Or what is it?

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