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.

326 questions with no upvoted or accepted answers
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14
votes
1answer
399 views

How to treat pressure in computational chemistry?

I have a reaction where a gas at high pressure and a solution with all kinds of species is involved. How do I take pressure correctly into account to get reasonable values for $G$? Do I calculate ...
8
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0answers
677 views

Entropy of Activation and Temperature Dependence

I am trying to understand the extrapolation of enthalpy $\Delta H^{\ddagger}$ and entropy of activation $\Delta S^{\ddagger}$ from the Eyring equation. It's typically cast as: $$\ln\left(\frac{k}{T}\...
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0answers
122 views

Why are IUPAC's definitions of exo- and endothermic disconnected from the direction of heat flow?

I'm wondering if anyone can provide a rationale for IUPAC's definitions of exothermic and endothermic, since they disconnect these terms from the direction of heat flow. Specifically, here are IUPAC'...
7
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2answers
344 views

Apparent contradiction in the type of deviation of an ethanol-water mixture

For a mixture of $\ce{EtOH}$ and $\ce{H2O}$: $\Delta H_{\text{mix}} < 0$ (exothermic) and $\Delta V_{\text{mix}} < 0$ (volume contraction). This means that the unlike interactions are stronger ...
7
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0answers
348 views

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 ...
6
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0answers
73 views

Why is concentration used as a proxy for activity instead of mole fraction?

I am trying to understand how the Gibbs energy change of a chemical reaction is computed and I do not understand why concentrations (mol/L) are used as a proxy for activity rather than mole fractions (...
6
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0answers
158 views

Anomaly in van der Waals constants of noble gases

In van der Waals equation for a real gas, the equation is $$\left(P + a\frac{n^2}{V^2}\right)(V - nb) = nRT$$ where $P$ is the pressure of the real gas, $n$ is the number of moles of the gas, $R$ is ...
6
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0answers
385 views

Thermophysical properties of liquid Galden LS 230 between 25 °C and 230 °C

I'm looking for thermophysical properties of Galden LS 230, a liquid polymer (PFPE) produced by Solvay (https://www.solvay.com/en/markets-and-products/featured-products/Galden.html) at temperatures ...
6
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0answers
174 views

I found transition states (TS), but calculations aren't supported by experiment. Do I look for more TSs or somewhere else?

I'm using Gaussian to investigate a catalyst system. Experimental evidence showed that one of three analogues (R = phenyl, Ph), yielded a benzosultam when treated with 2,4,6-...
6
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0answers
128 views

Seeking titanium compound, melting point <1600 °C, decomposes to TiO

The title says it all. I’m new to glass making, and I need a titanium compound that will render me $\ce{TiO}$ through decomposition, and has a melting point under 1600 °C. Hopefully I can get one ...
5
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0answers
53 views

Thermodynamics of micellisation

Micellisation is found to be spontaneous i.e. $\Delta G < 0.$ It's found that $\Delta S > 0,$ which was intuitive since, solvated molecules are released. And, it may be most loosely started that ...
5
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0answers
91 views

Reconciling Flory-Huggins Theory with Le Chatelier's Principle

(I discuss the Flory-Huggins parameter as chi from here onward). So I had learned in class that when discussing polymers the Flory-Huggins Theory helps us figure out whether mixing is ...
5
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2answers
256 views

Clausius–Clapeyron relation for states of water and vapor

I've seen many questions about this topic on this site, but I still have some issues trying to understand this aspect. Here's what I believe I understood looking at the phase diagram for a pure ...
5
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0answers
349 views

Compounds that Liberate Hydrogen from Water, Reversibly

I'm working on a paper which provides an overview of all the current methods for storing hydrogen gas as part of a renewable energy system, and I understand compressed gas and metal hydride storage ...
5
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0answers
89 views

Describing evaporation without entropy — what about Helmholtz?

I have in mind a rigid, impervious, heat-insulating vessel containing a monatomic liquid and vacuum. The vessel has an insulating forcefield inside, exactly at the surface of the liquid. It can be ...
5
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0answers
80 views

How can I compute the temperature change from the de-excitation of excited particle species?

The motivation for the question in the title is that I have some formula given, $$\Delta T=\frac{3410\ \gamma_{O_2}}{2.5+\gamma_{O_2}},$$ where $\gamma_{O_2}$ is the molar fraction of oxygen in a ...
5
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1answer
861 views

Entropy Change of Resistor

A very large swimming pool filled with water of temperature equal to $20\ \mathrm{^\circ C}$ is heated by a resistor with a heating power of $500\ \mathrm{W}$ for $20$ minutes. Assuming the water in ...
4
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0answers
48 views

Is entropy maximum in equilibrium?

Usually, in the context of non-equilibrium thermodynamics, it is said that entropy achieves a maximum in equilibrium, so the Taylor series expansion of entropy around the equilibrium state as a ...
4
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1answer
50 views

Thermodynamic model of inclusion process of alpha-cyclodextrin

I have a question about thermodynamic model of inclusion process of CD, published by Tabushi (DOI: 10.1021/ja00471a043). Here, in 3rd step, action is described as: "An apolar solute (guest molecule) ...
4
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0answers
33 views

Curtin-Hammett principle to evaluate alkene insertion

Given an unsymmetrical alkene in a simple non-stereoselective catalytic hydrogenation reaction. If one would want to investigate the nuances in the catalytic cycle of a dihydride complex leading to ...
4
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0answers
81 views

Has a concept of temperature ever been defined in the context of a single atom?

I wonder if this answer to What would happen if we supercool and then superheat an atom very abruptly? goes far enough. I almost wrote the comment: I don't think we can even talk about the ...
4
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0answers
59 views

Is pH in a charged hydrogel and its supernatant solution constant?

Let us assume we deal with ideal systems without interactions. The gel phase and the supernatant solution phase are in thermodynamic equilibrium. The supernatant solution shall consist of different ...
4
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0answers
279 views

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. ...
4
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0answers
52 views

Can a droplet of formalin evaporate in midair while falling?

I am designing an evaporator for use in an enclosed environment. Due to the hazardous nature of formaldehyde, I want my evaporator to be wick-free. The environment in which the evaporator will be used ...
4
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0answers
86 views

Can anyone explain this condensation pattern?

What is the hair-like polymer that condenses on the caps of the plastic cell vial? Inside vial are cells in a mixture of FBS and DMSO. The vials were frozen slowly in a special isopropanol-filled ...
4
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0answers
3k views

Theoretical temperature change in lime hydration

Calcium oxide (quicklime) and water have an exothermic reaction $\ce{CaO + H2O \rightarrow Ca(OH)_2} \quad \quad \Delta H^{\circ}_f=-65.3 \; \mathrm{kJ \cdot mol^{-1}}$ Assume that I have 1 kg of ...
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0answers
68 views

Glycine nucleation simulations

I am trying to run nucleation simulations of glycine in water. To generate a supersaturated solution, a solution that will crystallize, I need to know the solubility. Luckily for me, this data exists. ...
4
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0answers
154 views

Ratio of MbO2/Mb in a satured solution of dissolved oxygen from dry air

What is the ratio of $\ce{MbO2/Mb}$ if the solution is saturated with air? Details of the question: $$ \begin{align} \ce{Mb + O2 (aq) &-> MbO2}\\ \Delta G' &= -30.3~\mathrm{kJ/mol}\...
3
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1answer
301 views

Calculating ΔH from bomb calorimetry

Suppose we carry out a reaction in a bomb calorimeter whose starting temperature is $298.15\ \mathrm K$. Here we assume $\Delta V$ is close enough to zero that we consider the process to be at ...
3
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0answers
111 views

Why does standard reduction potential get multiplied by the change in oxidation state and not by the number of electrons transferred?

The whole basis of Frost diagrams is to have a graphical representation of the Gibbs free energy of formation ($\Delta{G}_{f}$) of different oxidation states of an element using the proportional ...
3
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0answers
128 views

If dG is a state function, why do reversible and irreversible paths differ?

For a reversible process at constant T,P in a closed system with no non-expansion work dG = 0. For an irreversible process under the same conditions, dG < 0. Since dG is a state function I would ...
3
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0answers
66 views

Reverse rate coefficient for thermolecular and thermal dissociation reactions

I am an astrophysicist working in exoplanetary atmosphere chemistry right now, in particular modelling the chemical kinetics taking place within the atmosphere. Based on this IOP article, we have that ...
3
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0answers
32 views

How is the number of successful collisions in a time-step distributed?

In a spatial homogeneous reaction system with two different molecules, how is the number of collisions which will lead to a reaction in a fixed time-step distributed? My guess: Poisson distribution, ...
3
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0answers
619 views

What is the relation between pressure and chemical potential?

I know that in a two-component gas-liquid system (for simplicity) the chemical potential $\mu_i$ ($i=1,2$) and total pressure $p$ can be defined by $$\mu_i=\left(\frac{\partial U}{\partial N_i}\right)...
3
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0answers
30 views

What dynamical features allow for the existence of a liquid-liquid transition?

Recently it has been shown theoretically[1] and then experimentally[2] that a liquid-liquid transition (LLT) takes place in pure supercooled water. That is to say, two distinct liquid phases have a ...
3
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0answers
119 views

Which term for heat energy in calorimetry is correct in scientific usage?

In calorimetry several terms are interchangeable: Lower Calorific Value Lower Heating Value Net Calorific Value Net Heating Value The following terms also appear to have identical meanings: Higher ...
3
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0answers
85 views

Which organic compounds have the most strongly negative enthalpies of formation?

I've been using the NIST Webbook to list organic compounds and look at their heats of formation (kJ/g, not mol). If I limit myself to three carbons, I still get over 400 results. I can use some ...
3
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0answers
162 views

Is free expansion of an ideal gas necessarily adiabatic?

I wanted to know if the term "free expansion" automatically implies an adiabatic vessel.Is it possible that there can be a transfer of heat in the free expansion of an ideal gas (as the term seems ...
3
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0answers
149 views

Hydrogen Peroxide Heat of Dilution

Based on some data here, I am getting the heat of dilution of 100% $\ce{H2O2}$ as approx. 1100 cal/mole. That's about 4.6 kJ/mol if I did my math right. Is this a correct value? Seems too low to ...
3
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0answers
529 views

Example of an endothermic reaction that can sustain itself for at least an hour?

Recall that in physical chemistry, the spontaneity of a reaction at constant pressure and a given temperature $T$ can be quantified by the Gibbs free energy $$\Delta G = \Delta H - T \Delta S$$ A ...
3
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0answers
405 views

Thermodynamics: Solving for Entropy, Gibbs and Helmholtz

A reversible melting of $32.0\ \mathrm g$ of ice at $0\ \mathrm{^\circ C}$ and $1\ \mathrm{atm}$. Solve for $\Delta G, \Delta S_\text{universe}$, and $\Delta A$ I'm also given latent heat of fusion/...
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0answers
497 views

Definition of “Diabatic” vs “Diathermic”

In Atkins' Elements of Physical Chemistry (Sixth Edition) it is written that: walls that permit heating as a mode of transfer of energy are called diathermic and that the converse situation is ...
3
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0answers
370 views

Minimizing Gibbs Free Energy for Multiphase Equalibria

I'm a geologist and don't have a strong background in chemistry or thermodynamics. Any help on solving this problem is much appreciated. I'm trying to minimize Gibbs free energy to get initial ...
3
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0answers
60 views

Expansion of ideal gas in isothermic conditions

I'm doing this problem and I get a different value than the answer in a book. I'm not sure if the book is wrong or me. At a constant temperature of $298~\mathrm{K}$, calculate $\Delta S_{\mathrm{...
3
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0answers
81 views

Clash between thermodynamic and kinetic processes

I have often come across reactions where kinetic and thermodynamic processes give completely different outputs. I was told that in such cases check temperature, if temperature controlled, then take ...
3
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0answers
690 views

Dissociation percentages of N2O4 at different pressures using Gibbs' free energy

\begin{align} \ce{N2O4(g)&<=>2NO2(g)} & \Delta_\mathrm{r}G^\circ &= \pu{4.7 kJ mol^-1} \end{align} Knowing that the standard values for pressure and temperature are $\pu{1 bar}$...
3
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0answers
863 views

Determining pressure of sublimation of iodine

The pressure of sublimation of iodine can theoretically be determined by considering the two hypothetical steps: the sublimation of iodine at $\pu{298 K}$, followed by an isothermal expansion of our ...
3
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0answers
297 views

Radial Distribution Function for a Hard Sphere Gas in the Percus-Yevick Approximation - Is There a Quick Way to Evaluate it Numerically?

The question is as in the title. I know that for a one-component hard-sphere gas, there is an analytic solution in the $\vec{k}$-space (PRA, 5, 939). I know that to obtain the correct solution in $r$...
2
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0answers
23 views

expression of apparent reaction quotient

question When computing the Gibbs energy change of a reaction using Legendre-transformed $\Delta_fG'$ values for a given $\mathrm{pH}$, the formula of the $\Delta_rG'$ of the reaction is: $\Delta_rG' ...
2
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0answers
42 views

Chemical Potential in the Fluorescent Molecule

I'm reading this paper, which states that the chemical potential $\mu$ is determined by the steady-state balance of up and down transitions in a fluorescent molecule. I am happy with this ...

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