Questions tagged [entropy]
For questions about the thermodynamical state function entropy, commonly understood as a measure of disorder.
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When a reaction is exothermic, how does it affect entropy?
In my textbook (Chemistry for Engineering Students 4th edition from Cengage), it states that an exothermic reaction generally does not change the entropy of the system. Why would the entropy not ...
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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 $H_2$....
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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 ...
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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 ...
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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 ...
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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 /...
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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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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 ...
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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 ...
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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 ...
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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 ...
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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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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 ...
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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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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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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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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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 ...
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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 ...
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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 ...
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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 ...
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Find the percentage of dissociation of nitrogen tetroxide given pressure, temperature, enthalpy and entropy
Given
$$
\begin{align}
\Delta_\mathrm f H^\circ(\ce{N2O4}) &= \pu{9.16 kJ mol^-1}
&\quad
\Delta_\mathrm f H^\circ(\ce{NO2}) &= \pu{33.18 kJ mol^-1}
\\
S^\circ(\ce{N2O4}) &= \pu{304.3 ...
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Why would a reaction be nonspontaneous at higher temperatures?
Typically we think of a higher temperature speeding up the reaction rate and/or supplying the activation energy of a reaction. So why is it the case that some reactions are only spontaneous at lower ...
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Total entropy change for reversible reactions and its relationship to equilibrium constant
I'm in year 12 of school doing A2 chemistry learning about entropy and its relationship to reversible equilibria. I learned about the following three ideas from my course book (verbatim), for a ...
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Use the first law of thermodynamics to derive the pressure as a function of T, U, V and N
I am struggling with a thermodynamics question given
$$S(U,V,N)=C_VNK_\mathrm b\ln U/U_0+NK_\mathrm b\ln V/V_0$$ (where $U_0$ and $V_0$ are the reference energies and volumes) and the first law of ...
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How is the entropy of mixing related to chemical reactions in solution?
When calculating the Gibbs energy of reaction for reaction mixtures at arbitrary concentrations, you use the following expression:
$$\Delta_\mathrm r G = \Delta_\mathrm r G^\circ + RT\ln Q$$
The term $...
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Is the entropy change positive or negative in this reaction?
Suppose I have a reversible reaction
\begin{align}
\ce{A(g) + B(g) <=> C(g)}\\
\end{align}
with equilibrium constant K.
Its ΔΗ is positive throughout.
Now, suppose I start with 1 mole ...
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Spontaneity criterion for phase transformations and chemical reactions [closed]
Why is the Gibbs free energy (G) considered a spontaneity criterion for phase transformations and chemical reactions? Why are other thermodynamic parameters such as enthalpy (H), entropy (S), and ...
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Why is rapid expansion/compression reversible?
I am looking over the Otto Cycle on this MIT website and it says at one point "the processes from 1 to 2 and from 3 to 4 are isentropic" in reference to the expansion and compression of the ...
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What does it mean that the standard molar entropy value is the amount of energy that a substance must have to exist at a certain temperature?
What does it mean that the standard molar entropy value is the amount of energy that a substance must have to exist at a certain temperature?
According to this reference: http://khimiya.org/volume15/...
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Is there an equivalent term for favourable and non-favourable entropy?
For Gibbs energy, we have 'exergonic' or 'endergonic'
For Enthalpy, we have 'exothermic' or 'endothermic'
It seems logical there should be an equivalent pair of terms for entropy, but I can't seem to ...
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Effect of degree of freedom on entropy change during a reaction
In the reaction $$\ce{C_{(s)} + O2_{(g)} -> CO2_{(g)}} $$
one mole gaseous reactant gives one mole gaseous product, so there is no significant change in entropy. It can be verified by line of $\ce{...
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In regards to the Gibbs free energy equation, it seems that the two terms oppose one another, Enthalpy and -TS. Can you explain this?
So for example, if H is endothermic, then the enthalpy term is positive, meaning energy is absorbed by system overall, meaning net bonds broken, meaning the equation leans towards nonspontaneity. If ...
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Thermodynamics derivatives: Does $(\partial A/\partial B) = (\partial B/\partial A)^{-1}$?
If I need to find, for instance:
$$\mathcal{T} := \left(\frac{\partial U}{\partial S}\right)_{V, N}$$
knowing:
$$\left(\frac{\partial S}{\partial U}\right)_{V, N} = \frac{1}{T}$$
Can I say that $\...
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How does Entropy influence the racemization of an optically active compound?
We were doing the topic "Isomerism" in our Organic Chem class and there's a question in our worksheet whose answer I haven't really understood, the question is as follows:
The racemization ...
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Can entropy of universe remain constant in a process where P and T is constant?
We know $$\Delta S(\text{univ})=\Delta S(\text{sys})+\Delta S(\text{surr})$$ at constant $P$, $T$.
$$\Delta S(\text{sys})=\Delta H(\text{sys})/T$$
$$\Delta S(\text{surr})=\Delta H(\text{surr})/T$$
As $...
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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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What is heat bath here?
At the beginning $\pu{1 mol}$ of air is compressed to $\pu{3 atm}$ at a of temperature $\pu{523 K}$. After a random process, the pressure of the air equates to $\pu{1 bar}$ at a temperature of $\pu{...
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If the reaction is spontaneous, is it the ΔS surroundings that is always positive or ΔS universe? [closed]
If the reaction is spontaneous, is it the ΔS surroundings that are always positive or ΔS universe?
I tried researching this on Google. However, the answers that I have found vary with different ...
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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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Question regarding Entropy [closed]
I had some doubts regarding the concept of entropy. My first doubt was
Entropy is defined as $ dS = dQ _{rev}/ T $ yet my textbook says that entropy is a state function. Isn't it the definition of a ...
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Loss of entropy and solvation energy in proteins
I am reading a chapter on protein stability. One section outlines the role of salt bridges or ion pairs in the stability of a protein. The excerpt goes as follows (italization added for emphasis):
...
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What is an example of an exothermic reaction with negative ∆S?
In high school we learn that when a reaction has both negative $\Delta{}S$ (entropy change) and negative $\Delta{}H$ (enthalpy change) it occurs spontaneously at lower temperatures, but becomes non-...