Questions tagged [entropy]
For questions about the thermodynamical state function entropy, commonly understood as a measure of disorder.
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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 ...
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Standard Free Energy of Formation and Reaction Coefficients [duplicate]
Consider the following reaction:
$$\ce{N2 + 3H2 \to 2NH3}$$
I want to calculate the enthalpy involved in the reaction.
I have been given the standard free energy of formation of $\ce{NH3}$, $\ce{N2}...
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28 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 ...
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29 views
Calculate change in entropy when both temperature and volume change
Calculate the change in entropy when $\pu{23.5 g}$ of oxygen gas is heated from $\pu{240 K}$ to $\pu{360 K}$ in such a way that its pressure increases from $\pu{2.00 kPa}$ to $\pu{8.00 kPa}.$ Assume ...
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1answer
51 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 ...
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1answer
52 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 ...
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1answer
38 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 ...
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2answers
42 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, ...
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1answer
49 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 $\...
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1answer
35 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 ...
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1answer
64 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).
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2answers
87 views
Relationship between the ideal gas constant and entropy
So it dawned on me the other day that the ideal gas constant $$R = \pu{8.31 J mol-1 K-1}$$ has the same units as molar entropy. Is there some deeper meaning behind this or is it just a coincidence ...
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Whether the entropy change of the system is positive or negative
$$\ce{N2(g) + O2(g) → 2NO(g)}$$
My thinking: since gases are combined together, so there randomness or disorder gets decreased. Hence the sign of entropy change of the system should be negative.
...
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2answers
106 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
$$\Delta S_\mathrm{tot} = \Delta S_\mathrm{sys} - \frac{\Delta H}{T}$...
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1answer
86 views
How does refrigerator actually work?
In refrigerator, heat energy got extracted from cold sink and dumped into hot source. This is not spontaneous so work must be done. I came across the following while reading a textbook:
For ...
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1answer
191 views
Effect of temperature on equilibrium constant in terms of entropy change
This question was asked in the JEE examination of 2017 :
[A] option is incorrect since the system is losing heat and hence $$ \Delta S = -ve$$
[B] Lets assume we have an endothermic reaction $$\...
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3answers
125 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
536 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
40 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 ...
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2answers
162 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
83 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
48 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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28 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
181 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
54 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
148 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
40 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
233 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
38 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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151 views
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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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
221 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
30 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
$$\ce{O2(g) + C(s) -> CO2(...
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1answer
144 views
Where can I find the standard molar entropy for ammonium bicarbonate?
I'd like to know the standard molar entropy S0solid for ammonium bicarbonate to use in an example in class, to calculate ΔS0 for the reaction, NH4HCO3(s) → NH3(g) + H2O(g) + CO2(g).
Already checked: ...
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1answer
106 views
Entropy change of evaporating NaCl [closed]
What is $\Delta S$ for this process?
$$\ce{NaCl(s) -> NaCl(g)}$$
(A reference that I could quote would be ideal.)
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1answer
112 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
146 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
138 views
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 ...
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1answer
357 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
940 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, ...
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2answers
143 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
609 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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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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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
5k views
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
583 views
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
158 views
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
76 views
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 ...
