Questions tagged [entropy]
For questions about the thermodynamical state function entropy, commonly understood as a measure of disorder.
240
questions
1
vote
1answer
73 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
36 views
How to find entropy of chemical network reaction?
I have the following system of reactions:
$$
\begin{aligned}
\ce{X_1 + Y_1 &<=>[$k_{21}$][$k_{12}$] X_2} \\
\ce{X_2 &<=>[$k_{32}$][$k_{23}$] X_3} \\
\ce{X_3 &<=&...
0
votes
1answer
32 views
Is entropy of surroundings a state function?
It is a pretty common well known fact that the entropy of a system is a state function ie. it doesn't depend upon the path taken by the process as long as the initial and final states are the same.
I ...
2
votes
1answer
65 views
What's the minimum amount of energy needed to remove CO2 from the atmosphere?
I've been learning about CDR (Carbon Dioxide Removal) techniques to combat climate change. These all seem to involve extracting $\ce{CO2}$ from the atmosphere and converting to a mineral, which is ...
2
votes
1answer
78 views
How does the entropic force arise within the hydrophobic effect?
I know that the hydrophobic effect is usually explained by the entropic effect originating from the disruption of hydrogen bonds between molecules of water and the nonpolar substance. The hydrogen ...
4
votes
0answers
42 views
Is entropy maximum in equilibrium?
Usually, in the context of non-equilibrium thermodynamics, it is said that entropy achieves a maximum in equilibrium, so the Taylor series expansion of entropy around the equilibrium state as a ...
1
vote
1answer
75 views
A Curious (definitely wrong) result of Absolute Entropy [closed]
The Gibbs free energy is defined as
$$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, $...
0
votes
0answers
48 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 ...
1
vote
1answer
46 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
1answer
44 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 ...
10
votes
3answers
699 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 ...
4
votes
2answers
68 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
46 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 ...
2
votes
2answers
79 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
1answer
308 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
72 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
52 views
TāS 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 ...
1
vote
1answer
41 views
Is constant pressure heat capacity = entropy during adiabatic reversible expansion of perfect gas?
For any process, āG = āH - ā(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
āG = āH - SāT
The ...
0
votes
1answer
65 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 ĀŗC ...
4
votes
2answers
414 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 ...
-2
votes
1answer
60 views
Why does the combustion of graphite have a positive Delta S?
The following reaction is exothermic and entropically favorable:
$$\ce{C (s) + O2 (g) -> CO2 (g)}$$
My question: Why is this reaction entropically favorable?
Clearly there are more ways to arrange ...
10
votes
2answers
1k views
Can someone intuitively explain the reason for the units of entropy (J/K )? [duplicate]
If entropy is just a measure of the "randomness" or "chaos" of a system, then why does it have specific units. What is the reason behind the units of entropy being J/K?
3
votes
0answers
35 views
Discussion about Warren-Cowely Parameter
The Warren-Cowely Parameter (WCP) for short range solution order is defined as:
$$\mathrm{WCP}_{ij} = 1 - \frac{Z_{ij}}{x_j \cdot Z_i}$$
where $Z_{ij}$ is the partial Coordination Number (CN) of ...
2
votes
2answers
59 views
Can you approximate the change in entropy of a reaction?
I found a problem in which I am given a hypothetical reaction in which from 2 liquids (reactants) I get 4 moles of gas and 1 mole of a solid substance (products):
$$\ce{A (l) + B (l) -> 4C (g) + ...
2
votes
1answer
46 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. ...
0
votes
0answers
28 views
Why don't we use standard entropies of formation?
In almost any appendix, the standard enthalpies and standard free energies of formation are listed. Why is the standard entropy of formation not relevant? Why do we use the standard molar entropy ...
7
votes
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 ...
3
votes
1answer
79 views
Gibbs energy: the term āTdS. Where does the reversible heat go?
When we have an exothermic reaction as well as a decrease of the entropy in the system after the reaction, why does the decrease in the entropy of the system diminishes the amount of useful work we ...
1
vote
1answer
92 views
Entropy as a state function independent of the path
When entropy is a state function and the entropy change for a reversible process is
$$\mathrm dS_\mathrm{rev} = \frac{\delta Q_\mathrm{rev}}{T} = 0,$$
how can an irreversible process be ...
0
votes
0answers
54 views
Adiabatic compression of an ideal monatomic gas. What would the change in entropy be?
Two moles of an ideal monatomic gas initially at 300K and a pressure of 2 atm is compressed adiabatically using a constant external pressure $P_{ext}$ until equilibrium is reached. The temperature of ...
0
votes
2answers
65 views
Clarification required on whether to use $C_v$ or $C_p$ in this question on finding entropy change
$1 \text{ mol}$ of an ideal monoatomic gas at $300 \text{ K}$ is subjected to a reversible isentropic compression process until final temperature reaches $600 \text{ K}$. If initial pressure is $1 \...
-1
votes
1answer
110 views
Gibbs free energy for an ideal gas
You know that for a generic system which during a process exchanges heat with a reservoir at a constant temperature $T_{a}$ it holds:
$$\Delta G=\Delta H-T_{a}\Delta S$$
Where:
$\star)$$\Delta G$ is ...
1
vote
2answers
149 views
What is wrong in this argument that dG must always be zero?
Under constant temperature and pressure, the change of the Gibbs free energy can be written as
$$\mathrm dG_\textrm{sys} = \mathrm dH_\mathrm{sys} - T\,\mathrm dS_\mathrm{sys}$$
And in the textbook ...
0
votes
1answer
55 views
Troubles with Gibbs free energy
The book I'm reading writes that for a system at constant pressure and temperature it holds:
$$dG=-TdS_{tot}$$
where $dG=dH-TdS$.
So if you want to see if a certain process is spontaneus, you just ...
2
votes
2answers
82 views
Entropy as an intrinsic property of matter
I would like to ask how we can see entropy as an intrinsic property of molecules, namely as something depending also on their geometry (and not only as gross disorder). Is this what is called the "...
1
vote
0answers
56 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 Ā°C}$ $(890),$ which was 70% higher than the ...
2
votes
0answers
26 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 ...
0
votes
1answer
56 views
Irreversible Adiabatic Process [closed]
While studying about the entropy change of surroundings in irreversible adiabatic process, I came across a sentence.
For infinite reservoir, all processes are considered reversible
And suddenly ...
1
vote
2answers
49 views
Spontaneity of an exothermic chemical reaction
When the process is exothermic (ĪHsystemā<0), and the entropy of the system increases (ĪSsystemā>0), the sign ofĀ ĪGsystemā is negative at all temperatures. Thus, the process is always spontaneous.
...
0
votes
1answer
412 views
Entropy changes during transfer of heat between two bodies
Consider two metal blocks, one at 500K and another at 300K, they are bought to contact with each other until they reach a common temperature.
Find the entropy change of each object and the total ...
4
votes
1answer
255 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
vote
0answers
147 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 ...
1
vote
0answers
34 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 ...
0
votes
1answer
1k views
Entropy change in non-ideal solutions
We know that some solutions show positive deviations and some show negative deviation from Raoult's law.The former is endothermic and the latter is exothermic. And again, the volume change show ...
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 ...
0
votes
1answer
217 views
Why is the entropy of solidifying solution higher than that of a pure solvent?
According to a source,
Solutions have a greater entropy than pure liquids as the particles in a solution are more separated and solvent molecules separate the solute particles. If the number of ...
1
vote
2answers
70 views
Can entropy in a closed system remain constant when you heat a liquid?
This is in regards to an exam question that I did not understand and got wrong.
The question was: When you heat acetone from 200 K to 400 K, what happens to the entropy?
Answers: Increases, ...
0
votes
1answer
55 views
Entropy and total differential
In an exercise, I have derived that
$$\mathrm dS_\mathrm{m} = \frac{3R}{2T}\mathrm dT + \frac{R}{V}\mathrm dV$$
using the 1st and 2nd law of thermodynamics (1 mol ideal gas).
Now, I want to write $\...
1
vote
1answer
364 views
Heat and work of glucose combustion
$$\ce{C6H12O6(s) + 6 O2(g) -> 6 CO2(g) + 6 H2O(g)}$$
When looking at glucose combustion I found that the change in Gibbs free energy is greater than the change in enthalpy. If we assume the process ...
1
vote
1answer
317 views
Temperature dependency of enthalpy H and entropy S [closed]
In textbooks, I often read that the temperature dependency of the enthalpy of reaction $\Delta_\mathrm{r}H$ and the entropy of reaction $\Delta_\mathrm{r}S$ can be neglected (in a limited $T$-range).
...
