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

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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
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Why does entropy increase on mixing two ideal liquids?

Why does entropy increase when we mix two ideal liquids? In my opinion entropy shouldn't change. Say we have two beakers of equal volume filled with $\ce{H2O(l)}$. I mark them red and blue (the ...
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Entropy change during rusting of iron [closed]

In my book I have a solved question: $$\ce{4 Fe(s) + 3 O2(g) -> 2 Fe2O3(s)}$$ For that reaction: $$\Delta H=-1648\ \mathrm{kJ/mol},\ \Delta S=-549.4\ \mathrm{J/(K\ mol)}\ \text{at}\ 298\ \mathrm K$$...
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Entropy changes of system/surroundings in irreversible adiabatic process [closed]

I recently came across a statement in a test which said "Neither reversible nor irreversible adiabatic process can cause a change in entropy of surroundings". This statement was given to be ...
Yes's user avatar
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Why is the entropy change of surroundings in free expansion zero?

I have read that what differentiates an irreversible process like adiabatic free expansion from its counterpart reversible process — isothermal expansion, which takes the system to the same final ...
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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
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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
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How to use the thermodynamic identity in a reversible process

I have trouble wrapping my head around the thermodynamic identity. From Schroeder's book "An Introduction to Thermal Physics," I understand that entropy is defined as $$\mathrm dS=\frac{δQ}T\...
DracoArtist's user avatar
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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
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Change in entropy with micelle formation

Micelles are formed only above the Kraft temperature. We know ∆G = ∆H - T∆S (Gibbs energy relation). For micelle formation to be spontaneous, ∆G has to be negative. This implies ∆H - T∆S has to be ...
EagerToLearn's user avatar
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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
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Spontaneity of endothermic reactions [closed]

I see the Gibbs Free Energy explanation everywhere, but is there an intuitive explanation of how endothermic reactions can happen spontaneously? It seems intuitively reasonable that heat flows from ...
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Entropy of the system is different for irreversible and reversible adiabatic process?

Entropy change of a system is a state function... But if we consider reversible adiabatic process, the entropy change of the system is zero, whereas the entropy of the system is greater than zero in ...
Natasha J's user avatar
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Why does graphite have a higher standard molar entropy than diamond?

It is known that graphite (5.7 J/K mol) has a higher standard molar entropy than diamond (2.4 J/K mol) (data from Physical Chemistry by Atkins). I understand that this must be due to the structural ...
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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
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Sign of ∆S in conversion of diamond to graphite

It is said that ∆S is positive as randomness is increasing from diamond to graphite as in diamond molecules are tightly packed together but we know that ∆S=∆H/T for phase transition and that ...
S K's user avatar
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Why does the second law of thermodynamics imply that processes with positive entropy change are spontaneous

My understanding of the second law is that for an isolated system, the entropy change accompanying any process is non-negative and is zero if and only if the process is reversible. I don't see why ...
Johnny Smith's user avatar
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Physical meaning of term T∆S

Plot "I assume the role of an attentive observer, carefully watching a chemical reaction unfold within a sealed container. This enclosed environment, completely closed ( no matter but energy can ...
Bharat Prajapat's user avatar
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2 answers
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Why Entropy is not related to work but heat?

We know that entropy of a system only depends on heat energy (supplied to or extracted from system) not on any other work (expansion work + non expansion work) by mathmatical expression ∆S = dQrev /...
Govind Prajapat's user avatar
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Why does Clausius inequality exist if entropy is a state function?

In Atkin's Chemical Principles: The Quest for Insight, the Clausius inequality is said to be $$\Delta S \geq \frac qT$$ where equality applies to a reversible process. Why would the change in entropy ...
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How to Calculate Entropy Changes at Non-Standard Conditions

I am trying to calculate the values of $\Delta H$ and $T\Delta S$ for the reaction taking place at $\pu{800 ^\circ C}$ $$ \ce{CO2 + H2O + 2CH4 -> 3CO + 5H2} $$ I calculated $\Delta H$ to be $\pu{\...
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3 answers
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How can entropy of universe or surroundings be a state function?

If a system goes from state A to B in a reversible process, then $(\Delta S)_{\text{universe}}=0$. However, my confusion starts if we take an irreversible route. For the system, even if we take the ...
user15141432's user avatar
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Reversibility for Entropy Changes in Chemical reaction

There is a problem in my textbook that asks to calculate the entropy change in surroundings for the Haber process, assuming that the enthalpy change is -92.4 kJ/mol. The solution to this problem is to ...
Manan Vij's user avatar
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Is q=0 for irreversible adiabatic process?

Well, I am a little bit confused about this question. I learn that reversible adiabatic processes are isentropic. So $\Delta S=0$. Through $\Delta S=\frac{ q}T$, we can say that $q=0$. But if you take ...
Sanjay's user avatar
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How do I find entropy change for surroundings?

I know how to calculate entropy change of the system but am not able to calculate entropy change for surroundings. The question is as follows: Q: At $100°C$, water vapour at $1$ bar is in equilibrium ...
Natasha J's user avatar
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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 ...
opa's user avatar
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Can anyone help me with the derivation for the formula of entropy?

I have this formula in the chapter of thermodynamics: $$\Delta S = n C_v \ln\left(\frac{T_2}{T_1}\right) + n R \ln\left(\frac{V_2}{V_1}\right),$$ where $\Delta S$ is entropy, $n$ moles, $C_v$ molar ...
rushi's user avatar
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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 ...
Natasha J's user avatar
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Phrasing for processes that "create" Entropy?

In many circumstances, in the real world, systems aren't "closed" in any meaningful sense. So, when I burn a log in a fireplace, I can use words to artificially set up a kind of "log ...
Him's user avatar
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What is the entropy change in isochoric process

I have studied that entropy increases with increase in temperature and it decreases with increase in pressure but in case of isochoric process both are happening at the same time but still the overall ...
Shashank j's user avatar
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2 answers
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How exactly is heat supplied in an isothermal process

How exactly is heat supplied in an reversible isothermal process. If the temperature of system and surroundings always remains the same, then how come surrounding is supplying heat? I studied that T ...
Shashank j's user avatar
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1 answer
168 views

What processes generate entropy as heat flows across temperature gradient

Suppose, we have a source at high temperature $T_\mathrm h$ and sink at temperature lower temperature $T_\mathrm l$. If $Q_\mathrm h$ amount of heat flow from source to sink, then change in entropy of ...
Natasha J's user avatar
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Question about entropy generated in isothermal expansion of an ideal gas

So, this has been bugging me for a while. Consider the isothermal expansion of an ideal gas in a container. As the gas is allowed to expand, it does work on the surroundings which causes the ...
Natasha J's user avatar
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Is delta S of universe always 0 when an ideal gas undergoes an isothermal irreversible process?

Since for an irreversible process, $$dS_\mathrm{Surrounding} =-\frac{\text{dq}_\mathrm{irr,sys} }{T_{\text {surr }}}\tag{1}$$ where $\text{dq}_\mathrm{irr,sys}$ is heat exchange of system and $-dq_\...
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1 answer
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Can we interpret the number of micro states calculated from molar entropy?

Forgive me if this is not the correct place to ask this. When I encounter a molar entropy, is it possible to rearrange the Boltzmann entropy formula $$S=k\log W$$ and meaningfully interpret the number ...
Henry's user avatar
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2 answers
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How are fundamental equations valid for both reversible and irreversible processes?

We know for an irreversible process, $\mathrm dS\gt\mathrm dq/T$. And if the process is done at constant pressure we can take the equation as $\mathrm dH-T\,\mathrm dS\lt0$. And we defined Gibbs ...
charith's user avatar
1 vote
2 answers
102 views

Can Vdp work be considered irreversible work (e.g., production of entropy)?

Since conduction across a finite temperature difference will produce entropy, will work done due to pressure difference generates entropy because system tends towards mechanical equilibrium which ...
ubuntu_noob's user avatar
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2 answers
525 views

If entropy is a state function, how can it be calculated for both reversible and irreversible processes?

$$\Delta S = nR\ln( V_2/V_1)$$ The value of ΔS of the system is independent of the path between the initial and final states, so this expression applies whether the change of state occurs reversibly ...
VANDERMIR's user avatar
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Find the percentage of dissociation of nitrogen tetroxide given pressure, temperature, enthalpy and entropy

Given $$ \begin{align} \Delta_\mathrm f H^\circ(\ce{N2O4}) &= \pu{9.16 kJ mol^-1} &\quad \Delta_\mathrm f H^\circ(\ce{NO2}) &= \pu{33.18 kJ mol^-1} \\ S^\circ(\ce{N2O4}) &= \pu{304.3 ...
Acedium 20's user avatar
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2 answers
550 views

Why would a reaction be nonspontaneous at higher temperatures?

Typically we think of a higher temperature speeding up the reaction rate and/or supplying the activation energy of a reaction. So why is it the case that some reactions are only spontaneous at lower ...
Jaccob W's user avatar
4 votes
2 answers
481 views

Total entropy change for reversible reactions and its relationship to equilibrium constant

I'm in year 12 of school doing A2 chemistry learning about entropy and its relationship to reversible equilibria. I learned about the following three ideas from my course book (verbatim), for a ...
Typo's user avatar
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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 ...
Yona Romes's user avatar
3 votes
3 answers
426 views

How is the entropy of mixing related to chemical reactions in solution?

When calculating the Gibbs energy of reaction for reaction mixtures at arbitrary concentrations, you use the following expression: $$\Delta_\mathrm r G = \Delta_\mathrm r G^\circ + RT\ln Q$$ The term $...
Karsten's user avatar
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Is the entropy change positive or negative in this reaction?

Suppose I have a reversible reaction \begin{align} \ce{A(g) + B(g) <=> C(g)}\\ \end{align} with equilibrium constant K. Its ΔΗ is positive throughout. Now, suppose I start with 1 mole ...
Half Infinity's user avatar
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2 answers
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Spontaneity criterion for phase transformations and chemical reactions [closed]

Why is the Gibbs free energy (G) considered a spontaneity criterion for phase transformations and chemical reactions? Why are other thermodynamic parameters such as enthalpy (H), entropy (S), and ...
Akshit Dhillon's user avatar
3 votes
1 answer
269 views

Why is rapid expansion/compression reversible?

I am looking over the Otto Cycle on this MIT website and it says at one point "the processes from 1 to 2 and from 3 to 4 are isentropic" in reference to the expansion and compression of the ...
one two's user avatar
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What does it mean that the standard molar entropy value is the amount of energy that a substance must have to exist at a certain temperature?

What does it mean that the standard molar entropy value is the amount of energy that a substance must have to exist at a certain temperature? According to this reference: http://khimiya.org/volume15/...
bananenheld's user avatar
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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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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
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3 answers
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In regards to the Gibbs free energy equation, it seems that the two terms oppose one another, Enthalpy and -TS. Can you explain this?

So for example, if H is endothermic, then the enthalpy term is positive, meaning energy is absorbed by system overall, meaning net bonds broken, meaning the equation leans towards nonspontaneity. If ...
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