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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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564 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}\...
7
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0answers
141 views

Computational heat of reation vs. using literature values

My question is I don't understand how to explain why or what I did wrong to have such large differences between my computational heat of reaction and heat of reaction using enthalpies of formation ...
7
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0answers
337 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
125 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 ...
6
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0answers
205 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
188 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 ...
6
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0answers
112 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
62 views

Contribution of vibrational degrees of freedom

The ratio $\frac{\mathrm{C_p}}{\mathrm{C_v}}$ for linear triatomic molecules including vibration contribution is given by: ? Attempt: We are aware that $C_v = \frac{fR}{2}$ and $C_p = C_v+ R$ ...
5
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0answers
73 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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0answers
145 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-...
5
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0answers
82 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
77 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 ...
4
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0answers
49 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
30 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, ...
4
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0answers
63 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
317 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
2k 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 ...
4
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0answers
64 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
135 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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0answers
51 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. ...
3
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0answers
52 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
94 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
44 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
302 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
29 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
107 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
votes
0answers
75 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
votes
0answers
114 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
votes
0answers
163 views

Effect of Temperature on Chemical Reaction Equilibrium

here is the question (part I): For part (i), I need some assistance, I cannot figure out how to do the question. I know eventually what to do, it's just working out the equilibrium constants I'm ...
3
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0answers
1k views

Calculating the Activity Coefficient parameters form Henry's Law

Here is the question, I am stuck on part B: Basically, this is my thought process so far, as $x_a \rightarrow 0$, the Henry's law line becomes tangential to the actual partial pressure curve.. Henry'...
3
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0answers
5k views

dU/dV in van der Waals equation of state derivation

Previous, I proved that $$\frac{T_2}{T_1}^{C_V/(C_p-C_V)}=\frac{V_1}{V_2}$$ I've been asked to derive a similar expression for a gas that obeys the equation of state $$p=\frac{RT}{(\overline{V}-b)}$...
3
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0answers
2k views

Experimental heat of solution much higher than expected?

I conducted an experiment in which $2.0\ \mathrm g$ of $\ce{NaOH}$ was dissolved in $200\ \mathrm{mL}$ of distilled water. This took place in a well isolated calorimeter. A temperature probe was used ...
3
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0answers
89 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
331 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 ...
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0answers
359 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
324 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
votes
0answers
189 views

Active mass,Pressure and concentration

The concentration is connected to the activity via $$a(\ce{A})= \gamma_{c,\ce{A}}\cdot{}\frac{c(\ce{A})}{c^\circ},$$ where the standard concentration is $c^\circ = 1\:\mathrm{mol/L}$. At reasonable ...
3
votes
0answers
52 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
73 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
692 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 ...
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0answers
264 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
votes
0answers
128 views

What is the ideal temperature and pressure to crack water?

Using sun mirrors and solar cells for electricity. What temperature, pressure and voltage ideal for cracking water. Source: NPR Source Would it take more or less electricity to crack water under ...
2
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0answers
40 views

Existence of single ion activities

I have used Davies equation to find what I believed was single ion activities and multiplied them on concentrations to define the thermodynamic dissociation constants for any kind of buffer to find ...
2
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0answers
99 views

What factors contribute in making a solution more endothermic?

For example, a solution between potassium nitrate and water is more endothermic than sodium nitrate in water. Can someone explain?
2
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0answers
29 views

Boltzmann Transport equation: Is df/dt=o for collisionless only?

$$\frac{\mathrm df}{\mathrm dt} = \left(\frac{\partial f}{\partial t}\right)_\text{force}+\left(\frac{\partial f}{\partial t}\right)_\text{diff}+\left(\frac{\partial f}{\partial t}\right)_\text{coll}$$...
2
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0answers
77 views

How do the pressure acting on the reactants and the initial temperature of the reactants affect the enthalpy of reaction?

In an exothermic reaction that occurs under constant pressure, does the pressure acting on the reactants affect the enthalpy of reaction? Does the initial temperature of the reactants affect the ...
2
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0answers
446 views

Is a low specific heat capacity for the material of the calorimeter good or bad?

I wish to ask if a low specific heat capacity of the material of the calorimeter means that the calorimeter would be more exact as it takes less heat for the material to reach equilibrium. I thought ...
2
votes
0answers
43 views

Why is the activation energy for 1,2-addition less than that for 1,4-addition to conjugated dienes?

1,2-addition proceeds faster than 1,4 addition making excess of 1,2-adduct at low temperatures. Also, since conversion of 1,2-adduct to 1,4-adduct is faster than the reverse, 1,4-adduct is in excess ...
2
votes
0answers
52 views

Thermodynamic Functions

Indicate the correct statements: a. $\mathrm{d}A = -S\mathrm{d}T$ for an ideal solution undergoing an adiabatic process. b. $\mathrm{d}G = -\mathrm{d}(TS)$ for an ideal solution undergoing ...
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0answers
93 views

How much energy water “captures” at it evaporates in room temperature?

As explained in Why does water evaporate spontaneously at room temperature despite ΔG > 0? water evaporates in room temperature because partial pressure of water is less than "standard" conditions ...