# Questions tagged [entropy]

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

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### 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 ...
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### Formula of entropy change

In my 12th standard book, the formula for entropy change is given as $\Delta S = \frac{q_\text{reversible}}{T}$. What is the importance of absorbing heat reversibly and not irreversibly? What does ...
5k views

### Why can entropy be measured in joules per kelvin?

I'm a little confused as to what the measurement associated with entropy represents. It's obviously the joules of energy per kelvin, but how does this measure the disorder of a system?
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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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### Entropy change in an adiabatic expansion

Question One mole of ideal gas initially at a pressure of 1 atmosphere and $T = 298\ \mathrm K$, is expanded into a volume 50 % larger adiabatically. In this adiabatic process, no work is done on ...
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### Entropy - "Wiggle"?

The title is not a reference to a Jason Derulo song. In any case: 1) How is change in entropy measured, experimentally? I've Googled this for a bit and I've found all sorts of mathematical ...
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### Is ΔS of a system related to temperature and change in enthalpy?

I often see the equation $\Delta S_\text{universe}$ = $\Delta S_\text{surroundings}$ + $\Delta S_\text{system}$, where $\Delta S_\text{surroundings}$ can be re-expressed in terms of the enthalpy ... 1k views

### Intuition on Gibbs Free Energy

In many places, I read that Gibbs Free Energy is called "free energy" because some of the enthalpy that comes from the chemical reaction becomes "waste heat" due to a change in the entropy of the ...
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### Derive expression for internal energy of mixing and entropy of mixing using statistical thermodynamics

I want to derive an expression for the internal energy of mixing, $\Delta_\mathrm{mix}U$, and entropy of mixing, $\Delta_\mathrm{mix}S$. The framework for this is the Lattice Theory of Ideal Solutions....
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My textbook reads as follows: When a gas is adsorbed, the freedom of movement of its molecules become restricted. This amounts to decrease in the entropy of the gas after adsorption, i.e. Entropy ...
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### Raoult's Law explained with thermodynamics/ free energy

I got some confusion going on with this explanation of Raoult's Law. This is what my book say: Because the ideal solution has a higher entropy than the pure solvent, the energy of a vapor ...
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### 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 ...
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### Calculating entropy change of surroundings

I have seen many similar questions but have not found my answer. Why do we use the actual heat involved in the process to calculate entropy change of surrounding? The only answer I can think of is ...
1 vote
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### Mechanism for Hydrogen Peroxide decomposition?

Someone asked this question earlier and made no attempt at understanding it on their own so the question was flagged. However, it prompted me to attempt to figure it out. This is what I have come up ...
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### Which temperature is meant in the Gibbs free energy equation? [closed]

In the equation for Gibbs free energy change, $\Delta G = \Delta H - T\Delta S$, does $T$ refer to the temperature of the system or the surroundings? I know we have to calculate Gibbs free energy of ...
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### If entropy is decreased when an enzyme-substrate complex is formed, how can the reaction be feasible?

Is it due to the bond formation creating energy that increases the entropy of the surroundings/universe?
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### On adding sugar to water, does the entropy increase or decrease?

This question is a little confusing. According to my teacher, the entropy should decrease, but I think that sugar is crystalline first and later it dissolves, so the randomness increases and so the ...
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### Is helium-4 a liquid at zero temperature and zero pressure?

As far as I know, for all substances other than helium, if you extrapolate the solid-gas line on the phase diagram, it passes through the origin. That is, no matter how low the temperature is, you can ...
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### Why can't a reaction go to completion?

What is the reason for why an exergonic reaction would still have some remaining reactants (or an endergonic reaction to have any products)? The explanation given on this page (see Chemical reactions ...
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### Does entropy contribute work?

I've seen that Gibbs free energy is defined as the maximum amount of work that a system can do. From this I gather, this is how much energy it will release - right? But, I've also learnt that the heat ...
660 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 ...
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### How can a nonspontaneous reaction occur?

$$\frac{-\Delta G}{T}=\Delta S_{universe}$$ (This equation applies under isobaric and isothermal conditions.) I understand that if $\Delta G$ is positive, the reaction is nonspontaneous, and adding ...
9k views

### Can one predict the entropy change for aqueous phase reactions without calculation?

I have seen several sources that claim aqueous solutions always have more entropy than pure liquids or solids, however, some aqueous ions have negative standard entropy. This opens the possibility of ...
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### Entropy and specific heat capacity

I have seen the equation $S(T_2)=S(T_1)+C_p\ln(T_2/T_1)$ where $C_p$ is the molar heat capacity at a constant pressure. I understand that this assumes that the temperature range is sufficiently small ...
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### Trying to Understand Entropy

I'm currently looking at Principles of Chemistry by Atkins, and I have a few questions involving entropy. These questions probably arise from my poor understanding of reversible/irreversible processes....
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### Truly Understanding the Second Law of Thermodynamics and Entropy

There are some seemingly contradictory things I’d like cleared up: Second Law states: $\mathrm dS_\text{univ} = \mathrm dS_\text{sys} + \mathrm dS_\text{surr}$, and $\mathrm dS_\text{univ}$ is always ...
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### Gibbs Free Energy and Entropy

I understand Enthalpy, the exchange of energy between products and reactants. But what is Gibbs Free Energy and Entropy? I know that Gibbs free Energy is the difference between the change in Enthalpy -...
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### Does minimizing ANY type of energy ALWAYS predict a state of equilibrium?

My intuition says no, but I am having trouble coming up with concrete examples. I know that minimizing Gibbs free energy predicts a state of equilibrium, while minimizing kinetic or internal energy ...
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### Which has maximum entropy

Which state has a higher entropy — the liquid–gas equilibrium or the gaseous state? I have learned that at equilibrium the entropy is maximised. But I also learned that the gaseous state has the ...
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### Can a reaction with positive Gibbs free energy change ever occur?

If you have an endothermic reaction with a negative entropy change, is it still possible to induce the reaction in some way despite the fact that the Gibbs free energy change is positive or all ...
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### How can -G/T and -A/T be thought of as 'disguised' entropies?

I understand that entropy is defined as $\mathrm{d}S=\mathrm{d}q/T$ for a reversible change but I fail to see why $-G/T$ and $-A/T$ can be thought of as 'disguised' entropies. This is a question on my ...
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This question was asked in the JEE examination of 2017 : [A] option is incorrect since the system is losing heat and hence $$\Delta S\lt0$$ [B] Lets assume we have an endothermic reaction \ce {... 3 votes 1 answer 9k 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 ... 3 votes 1 answer 518 views ### 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 ... 3 votes 2 answers 522 views ### Interaction between energy and entropy in highly elastic polymers? Consider the interaction of energy and entropy in the highly elastic materials of an ideal polymeric network. Now Gibb's free energy cannot be used directly \Delta H = \Delta G + T \Delta S where \... 3 votes 1 answer 3k views ### Why is the entropy of deuterium greater than that of hydrogen gas Why is the entropy of deuterium more than that of hydrogen gas? I thought about it but couldn't figure out a reason for why that would happen. Why would the number of neutrons in the nucleus ... 3 votes 4 answers 702 views ### Thermodynamics entropy and temperature In thermodynamics, whenever heat is released from the system to the surroundings, temperature of surroundings remains unchanged but entropy increases. But entropy is a function of temperature. How is ... 3 votes 1 answer 236 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 ... 3 votes 5 answers 1k views ### 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-... 2 votes 1 answer 11k views ### Entropy Change for mixing water at two different temperatures Assume that the heat capacity of water is independent of the temperature. Calculate the net entropy change when 1 mole of water at 0 degrees Celsius is mixed with 1 mole of water at 100 degrees ... 1 vote 1 answer 105 views ### Is constant pressure heat capacity = entropy during adiabatic reversible expansion of perfect gas? For any process, ∆G = ∆H - ∆(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 ∆G = ∆H - S∆T The ... 1 vote 0 answers 2k views ### Entropy change of surroundings The entropy change of a system is given by\mathrm dS=\frac{\mathrm dq_\text{rev}}{T}$$which at constant temperature is$$\Delta S=\frac{q_\text{rev}}{T} I also learned that the entropy change ...
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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 ...