# 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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### 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 - "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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### 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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### 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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### 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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### 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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### 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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### 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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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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### 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 ...
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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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### 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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### 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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### 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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### 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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### 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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