# Questions tagged [thermodynamics]

Applicable to questions about heat, energy, work, and their interconversion in chemistry. See the tag wiki for a detailed list of topics. Questions tagged may also be tagged with [enthalpy], [energy], [free-energy] where appropriate.

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### Question regarding enthalpy of sublimation vaporization and fusion

While learning Thermochemistry, I came across the formula $\Delta H_{sub} = \Delta H_{vap} + \Delta H_{fus}$ Now my question is how that when we want to change the phase of a substance from solid to ...
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### How to derive absolute temperature scale from Carnot engine?

This question is about how to obtain an absolute or thermodynamic temperature scale using a Carnot engine. The reasoning below appears in the book "Heat and Thermodynamics" by Zemansky and ...
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1 vote
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### Sign Conventions for Electron Affinity and Electron Gain Enthalpy [duplicate]

In some of the books, negative sign is used for an exothermic Electron Affinity. But in others, a positive sign indicates an exothermic Electron Affinity. Now if we adopt the first sign convention of ...
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### Can Gibbs Free Energy equation be used to explain why some phase changes are exothermic or endothermic?

I was wondering about some ways to explain why some phase changes are exo / endo. I am aware that for endothermic phase changes (boiling, melting, sublimation) energy input is required to raise the ...
59 views

### Why do we assume that entropy of H+ ion solution at 298 K is zero? [duplicate]

If we assume that entropy of H+ ion solution at 298 K is zero, then the entropy of other solutions which have less entropy than H+ will have negative entropy. But entropy is defined as the amount of ...
1 vote
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### Describing exothermic and endothermic processes using internal energy instead of enthalpy

IUPAC (https://goldbook.iupac.org/terms/view/E02269) defines exothermic and endothermic reactions using the sign (positive or negative) of the change in enthalpy of the reaction, which I think is ...
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### How is the Joule-Thomson coefficient related to the increase in temperature of the valve connecting bike pump to tire after pumping?

I was watching this lecture about enthalpy from a thermodynamics course (MIT OCW, 5.60, lecturer Moungi Bawendi). The lecturer goes through experiments and calculations to determine the coefficients (...
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### Gibbs free energy ( condition)

I want to derive Gibbs Free Energy formula from 1st and 2nd law of thermodynamics. I saw some texts using T and P constant in derivation. I am confused about that. If n,P, T are constant then its ...
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### Is there a homogeneity issue when two gases are mixed and filled in a vessel? [duplicate]

When two gases (one light and one heavy) are mixed in a 36m3 vessel (mole ratio 6.5%) is there a concern about the homogeneity of the gases (101 psi)??
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### Work done by using PV graph

One mole of an ideal monoatomic gas is subjected to changes as shown in the graph. What will be the magnitude of work done, in Joules? I know that work done $=$ area inside cyclic process Therefore, ...
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### Does the relation between ΔG° and K vary based on how they are changed?

From the equation ΔG° = ΔH° - TΔS°, I have always been taught that with +ΔH° and +ΔS°, the reaction would be favorable in cases with high temperatures and with +ΔH° and -ΔS°, the reaction would be ...
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### What is the particle speed in liquids at an average room temperature (20-25 degrees celcius)?

I've been searching online for ages and I can't find anything related to this, everything seems to be about gas particles relating to temperature. I'm investigating simple chemistry related to ...
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### Relation between dilution and osmotic pressure

The following question is taken from IAT 2024, an entrance test for research institutes in India at the high school level: Which one of the following plots correctly describes the variation of ...
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1 vote
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### Why is the entropy change of surroundings in free expansion zero?

I have read that what differentiates an irreversible process like adiabatic free expansion from its counterpart reversible process — isothermal expansion, which takes the system to the same final ...
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### Why is there no work in a free and adiabatic expansion of a gas? [closed]

I recently came across the topic of irreversible expansion in thermodynamics. Suppose we have a container of gas with a piston (not mentioned whether massive or not), and we allow a free and adiabatic ...
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### Calculation of Reaction Extent as a Function of Pressure and Temperature: Issue with Activity-Based Approach

I'm working on modeling reactions involving combinations of hydrogen (H), nitrogen (N), and strontium (Sr) elements. I've obtained the temperature-dependent Gibbs free energy of formation, enthalpy, ...
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### Confused about free energy equation and entropy change

I'm confused about two equations and how they relate to each other. These are $\Delta S = \Delta Q/T$ and $\Delta G = \Delta H - T\Delta S$. To derive the Gibbs' free energy change for the universe ...
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### Could an airborne swarm of small insects explode? [closed]

I know that fine-grained organic matter such as flour or pollen can be quite explosive if ignited. It also seems logical to me that the explosiveness of such an organic powder is determined by many ...
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### How does cell potential change with temperature for positive enthalpy and negative entropy?

A recent United States National Chemistry Olympiad question asked: A certain voltaic cell has a standard cell potential that increases with increasing temperature. Which best explains this ...
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