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 ...
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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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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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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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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 ...
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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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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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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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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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1answer
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Does adsorption violate thermodynamics?

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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1answer
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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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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 ...
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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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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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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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What is the difference between ΔG and ΔG "with an o on top"? [duplicate]

What is the difference between $\Delta G$ and $\Delta G^\circ$? I couldn't figure it out. Ex: $\Delta G^\circ = -RT\ln K$ $\Delta G = \Delta G^\circ + RT \ln Q$ What is the difference, is it that $\...
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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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3answers
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Is there a way to experimentally measure entropy?

I've been doing thermodynamic chemistry, and recently focusing on Gibbs Free Energy. Whilst doing calculations using, $$\Delta G = \Delta H - T \Delta S$$ I have been given a table of values for $\...
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What does the Clausius Inequality mean in thermodynamics? (entropy)

$$\delta S\ge\frac{\delta q}T$$ I don't understand how a quantity (the change in entropy in this case) can be greater than the very thing that defines it ($\mathrm{\frac{\delta q}{T}}$). Also what ...
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Where to find data for Gibbs energy, enthalpy, and entropy?

Where can you find the enthalpy and Gibbs free energy of formation and entropy of compounds either as a data file or web API? Technically, I only need two since I can figure out the other one from two ...
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1answer
454 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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569 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 ...
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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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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 ...
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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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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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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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1answer
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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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1answer
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 ...
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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 $\...
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When is a reaction reversible?

When speaking in thermodynamic terms, when is a reaction reversible? My attempt: A reaction is reversible when $\Delta\text{S} < 0$, because according to the second law of thermodynamics, "in ...
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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 ...
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1answer
182 views

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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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 ...
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1answer
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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 $$ \Delta S\lt0$$ [B] Lets assume we have an endothermic reaction $$\ce {...
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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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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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1answer
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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
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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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1answer
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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 ...
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1answer
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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 ...
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1answer
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Does all processes that consume energy from outside result in negative entropy change?

In any spontaneous process entropy increases.In biological systems disordered elements are converted into highly ordered tissues etc(-ve entropy change) which make up living organisms. But, it ...
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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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1answer
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Deriving the entropy of mixing of a non-ideal solution

In the earlier posted question named Derive expression for internal energy of mixing and entropy of mixing using statistical thermodynamics the entropy of mixing was found by assuming an ideal ...
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T∆S 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 ...
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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 ...