Questions tagged [entropy]
For questions about the thermodynamical state function entropy, commonly understood as a measure of disorder.
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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
$$\Delta S_\mathrm{tot} = \Delta S_\mathrm{sys} - \frac{\Delta H}{T}$...
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1answer
77 views
How does refrigerator actually work?
In refrigerator, heat energy got extracted from cold sink and dumped into hot source. This is not spontaneous so work must be done. I came across the following while reading a textbook:
For ...
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1answer
71 views
Effect of temperature on equilibrium constant in terms of entropy change
This question was asked in the JEE examination of 2017 :
[A] option is incorrect since the system is losing heat and hence $$ \Delta S = -ve$$
[B] Lets assume we have an endothermic reaction $$\...
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3answers
112 views
Estimating the absolute entropy of water at room temperature
I thought it would be fun to get an idea of how enormously large $W$ in $S = k\ln W$ is. I'd specifically like to estimate this for a mole of water at $\pu{1 atm}$ and $\pu{298 K}$. To do this, I ...
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2answers
236 views
Entropy change of isothermal irreversible expansion of ideal gas [duplicate]
Two mole of an ideal gas is subjected to isothermal expansion from $\pu{2 atm}$ to $\pu{1 atm}$ at $\pu{300 K}$. Calculate entropy change of the system, surrounding and total, if the process is ...
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1answer
39 views
When a piston cylinder system that evolves isothermally and quasistatically is irreversible?
Suppose we have two states: $\ce{A}$ and $\ce{B}$.
Considering a quasi-static isothermal process of an ideal gas, (and another condition, that is $T = T_\mathrm{surr}$) that join those states.
Then ...
2
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2answers
101 views
Hydrogen vs neon in terms of entropy
I know that both molecular size and complexity increase overall entropy, but between the two I'm not sure which increases it more. Would 1 mole of hydrogen have the greater entropy because it is two ...
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2answers
75 views
dSsur, dS and dStotal relation
By definition,
dS=dqrev/T.
Based on my understanding, the subscript rev means that the dq is heat exchanged in a reversible pathway from a state i to another state f, regardless of the actual ...
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1answer
42 views
How is “the surrounding” and its temperature defined to calculate entropy change during a reaction?
Lets say supercooled liquid water at $263\ \mathrm K$ isobarically changes to solid ice at the same temperature. I wish to calculate the change in entropy of the surroundings and I happen to know the $...
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0answers
24 views
Deriving the entropy as a function of concentration
In a physical chemistry class, the professor derived entropy $S$ as a function of concentration starting from $S=k\ln(W)$. Somehow he made a mistake and ended up with the wrong sign. This remains ...
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In dS≥dQ/T, material equilibrium means that there is not material changes at all or that a material change can be reversible and at equilibrium?
I am reading Levine's Physical Chemistry, I know how to arrive to that equation, but I have questions.
First, $\mathrm{d}S=\mathrm{d}Q/T$ for material equilibrium, but if there is a heat flow I ...
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1answer
78 views
Why are catabolic reactions exergonic and anabolic reactions endergonic?
Catabolism breaks apart large molecules and anabolism creates large molecules. Catabolism is supposed to be exergonic, while anabolism is supposed to be energonic. Id on't really understand this.
By ...
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1answer
24 views
How does the concentration of a gas affect the entropy of a system in a chemical equilibrium?
The question asks about factors that increase the entropy of the system. The mark-scheme states that "decreasing the concentration of a gas without changing the volume of the container" is the answer. ...
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1answer
89 views
Thermodynamic stability and Inertness [duplicate]
The following is from my teacher's notes:
The reaction (where the reaction mixture is thermodynamically unstable but kinetically inert) tends to go as indicated by a positive total entropy change, ...
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1answer
36 views
In chemistry what do they mean by disorder when in the context of entropy?
Entropy is often the amount of disorder is present in a system, but when they refer it to the degree of disorder in a system what do they mean. It just seems the term is quite vague and not very ...
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2answers
166 views
Why does ATP has a lower entropy than ADP
I was confused about why ATP has a lower entropy than ADP when ATP has 1 more phosphate group. According to https://chem.libretexts.org/Textbook_Maps/Biological_Chemistry/Metabolism/ATP%2F%2FADP#...
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1answer
36 views
An equal amount of hydrogen gas is dissolved in a 1L vessel and a 2L vessel, both filled with water. Which vessel has higher entropy? [closed]
This question came up in our chemistry class and we could not determine which would have the higher entropy. Clearly, Vessel 2 has a larger volume, but Vessel 1 has a higher concentration of $H_2$. ...
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0answers
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Molar entropy of vaporization
If a substance has a molar heat of vaporization of $\pu{3.05\times10^4J/mol}$ and a normal boiling temperature of $\pu{80.0^\circ C}$, what is the value of its molar entropy of vaporization $\Delta S_\...
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0answers
50 views
Why don't these Entropy equations contradict each other?
My textbook says that $\delta S_{rev}= \frac{q_{rev}}{T}$. It also says that $\delta S_{surr}= \frac{-q_{rev}}{T}$. Logically, this should mean that the change in entropy in both the surroundings and ...
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2answers
185 views
Absolute entropy
The third law of thermodynamics states that the absolute entropy of a pure crystalline substance is $0$ at $0\,\mathrm{K}$. In the analysis of chemical reactions this absolute scale is sued to ...
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1answer
29 views
Reaction direction change based on phase of reactants and products
I am curious specifically how the entropy of a reaction will change if the phases of the reactants and products at different conditions change.
For instance, a reaction
$$\ce{O2(g) + C(s) -> CO2(...
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1answer
76 views
Where can I find the standard molar entropy for ammonium bicarbonate?
I'd like to know the standard molar entropy S0solid for ammonium bicarbonate to use in an example in class, to calculate ΔS0 for the reaction, NH4HCO3(s) → NH3(g) + H2O(g) + CO2(g).
Already checked: ...
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1answer
74 views
Entropy change of evaporating NaCl [closed]
What is $\Delta S$ for this process?
$$\ce{NaCl(s) -> NaCl(g)}$$
(A reference that I could quote would be ideal.)
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1answer
97 views
What exactly is entropy? [closed]
I have looked at other questions, videos and articles but I kept reading disorganization, messiness or energy distribution (probability) or a thermodynamical equilibrium and stuff. What do we mean by ...
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1answer
126 views
Energy at constant Entropy and Volume
The system of constant entropy and constant volume will attain the equilibrium in a state of minimum energy. Why?
I know that:
$\Delta G= \Delta H-T\Delta S$
And at constant volume and entropy: $\...
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0answers
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How to compare standard entropy of diatomic gases?
Say, for example, I wanted to compare the standard entropies of $\ce{Cl2(g)}$ and $\ce{F2(g)}$. They both are equimolar.
I understand that entropy is a measure of how many states a particle can ...
5
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1answer
293 views
The confusion of entropy change
The entropy is defined as randomness of a substance or a system.
The randomness increases as we go from solids to liquids to gases. Similarly from hard diamond to soft graphite. Since graphite is soft ...
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2answers
751 views
Is it possible to determine the absolute value of entropy of a system?
I came across a question (in some assignments I had received) where it was asked:
Can the absolute value of entropy of a system can be measured?
and to my surprise, the answer said yes. Till now, ...
3
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2answers
120 views
Can the change in the entropy of the surroundings always be obtained by dividing heat transferred by the temperature at which the transfer occurs?
Consider $\pu{1 mol}$ of an ideal monoatomic gas going through reversible isochoric heating from $\pu{100 K}$ to $\pu{1000 K}$.
Calculate $\Delta S_\pu{sys}, \Delta S_\pu{surr}.$
$$\Delta S_\pu{...
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2answers
519 views
Entropy is a measure of unavailable energy?
I came across a statement in my text book which said that entropy is a measure of unavailable energy.
What does this statement signify?
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1answer
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How does the mathematical definition of entropy (ΔS=Qrev/T) give us the degree of disorder? [closed]
I think degree of disorder in thermodynamics means the number of possible locations that a molecule can take
How does the mathematical equation signify this?
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0answers
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Are volcanic eruptions a form of entropy? [closed]
My understanding of entropy is 'order to disorder' so I was thinking whether volcanic eruptions are a form of entropy since when magma leaves the crater it becomes lava. Is it more favourable for this ...
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0answers
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Change in Free Energy in Gas Reaction
I try to estimate whether particles form pairs or not.
What I know is the difference in the potential Energy $\Delta U_\mathrm{pot}$ which occurs when both particles form a pair.
When I have a ...
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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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1answer
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Does increasing the entropy of a system cause it to absorb heat?
This is my first time posting here, so bear with me. It was stated (in this video: https://youtu.be/7jT5rbE69ho?t=325) (Watch about the next fifteen seconds, until 5:40) that an increase in entropy ...
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1answer
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Change of temperature upon dilution
Consider a concentrated dye solution, say 10µM of Rhodamine 6G in water, which is rapidly diluted down to 10nM in an open container. I'm trying to estimate the (presumably minute) temperature change, ...
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1answer
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Does a polyethene shrinking signify negative or positive entropy?
When I think of something shrinking, I would intuitively think it decreases in entropy as there is less movement. E.g. if a gas was to reduce in volume, there would be less movement of the particles ...
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1answer
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Why does the Second Law of Thermodynamics hold true?
The Second Law of Thermodynamics states that the state of entropy of
the entire universe, as an isolated system, will always increase over
time. The second law also states that the changes in the ...
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1answer
93 views
Entropy at zero kelvin for pure atom crystal
The third law of thermodynamics describes that the entropy of pure ideal crystaline substance is zero.
Now we know that in practice this could be wrong for water (for example) because of its ...
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1answer
154 views
Understanding entropy / spontaneity
I have issues understanding the spontaneity for these processes:
Which of the following processes are spontaneous:
(c) alignment of iron filings in a magnetic field;
(d) the reaction of sodium ...
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1answer
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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 ...
2
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1answer
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Notation for specific/volumetric entropy
I'm working on a problem related to entropy, and for this particular use case it's advantageous to write down properties in 'specific' units. In the case of entropy (with units Joules over Kelvin, I ...
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1answer
403 views
Entropy and enthalpy at the melting point of benzene
For the melting of Benzene, since it is melting, it feels intuitive to think that the change in entropy will be positive (more disorder) and enthalpy will be positive (exothermic). However, when I ...
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0answers
131 views
Change in enthalpy and entropy for the formation of nickel tetracarbonyl
I was working on an enthalpy/entropy problem and I had a question on predicting the signs of some reactions. For the reaction
$$\ce{Ni (s) + 4 CO (g) -> Ni(CO)4 (g)}$$
my textbooks says that ...
3
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1answer
551 views
Why can we use standard entropy when determining temperature at which a reaction becomes spontaneous?
In this chemistry problem, $\Delta H$ and $\Delta S$ are given at $298\text{ K}$, and it asks for the temperature at which the reaction becomes spontaneous:
For the reaction $2\text{SO}_3 \...
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1answer
809 views
Adiabatic mixing of liquids
One mole of benzene at $\pu{20^\circ C}$ is adiabatically mixed with 2 moles of toluene at $\pu{40^\circ C}$. The heat capacity of benzene is $\pu{84 J K-1 mol-1}$ and the heat capacity of toluene is $...
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2answers
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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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2answers
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Why is “Spontaneous” a part of 2nd law wording?
The way I understand the law, any process is implausible if the total entropy of the universe does not increase. Why is "Spontaneous" even a part of the wording, what does it mean?
Is it perhaps a ...
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1answer
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Calculation of irreversible surrounding entropy
I have a specific query. In my undergraduate book Physical chemistry by Engel and Reid, sample problem 5.8 calculates the change in entropy of the surroundings and system for an irreversible ...
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Micelle formation [duplicate]
When micelles are formed... The movement of the molecules gets restricted so shouldn't it result in a decrease in entropy?
But it is said that increase in entropy is the driving force behind micelle ...
