# 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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### Why the Stoichiometric Coefficients are raised to the power of the concentration of the respective reactant? [duplicate]

While studying Chemical Kinetics, a question popped up in my mind that in Law of Mass Action, why the Stoichiometric Coefficients are raised to the power of the concentration of the respective ...
47 views

### What is the difference between standard Gibbs energy and Gibbs energy of formation?

Good day guys, I am reading a book on electrochemical engineering, I came across some definitions of Gibbs energy and I am a bit confused as the book does not go into a lot of detail. The book first ...
1 vote
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### Thermal conductivity and diffusivity of diatomite (also known as diatomaceous earth or kieselguhr)

Does anyone know where can I find measured thermal conductivity and thermal diffusivity of diatomite for different temperatures? I'm looking for the temperature dependency for temperatures higher than ...
59 views

### How to convert molar volume to volume?

This seems like a simple question that people must have asked already, but I can't find an answer online. I'm not a chemist, but need to use a code that deals with thermodynamics. I am trying to use ...
57 views

### How can enthalpy of an ideal gas be independent of pressure?

I know that when one applies a manipulation of the Ideal Gas Law to the Maxwell Relations the result that enthalpy is independent of pressure tumbles out of it, i.e., (dH/dP) = 0. I don't understand ...
1 vote
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### Change in internal energy at constant pressure versus heat released at constant volume

I am trying to solve a question that involves studying the heat released of a combustion process at constant pressure versus at constant volume. The question is The heat of combustion of ethanol ...
166 views

### Possible error in textbook question? (Heat transfer)

I am dealing with either (a) a severe misunderstanding of the question, or (b) a wrong textbook answer. Here is question verbatim: A jacketed vessel is used to heat a water stream using steam ...
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### How can I model the melting of ice as a function of time?

How much time it will take for a ball of ice at 0ºC and radius 3cm submerged in 1L of water at 100ºC to completely melt? (Assume the ice melts completely uniformly and treat it as a shrinking sphere) ...
34 views

### Critical point from ab initio calculations

I was wondering if it is possible to calculate the critical point (e.g., temperature, pressure, and density) other than via experiments or equations of state like ab initio calculations. Would anyone ...
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### Understanding Rossini and Frandsen experiment for measuring $(\partial u/\partial P)_T$?

In another question, I asked about the theoretical justification for the experiment that I will describe in what follows. The experiment was done by Rossini and Frandsen in 1932 at the National Bureau ...
1 vote
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### Justification for this theoretical experiment to measure temperature change during Joule expansion?

I am reading the book Heat and Thermodynamics 7th Edition by Zemansky and Dittman. There is a section of a chapter that I would like to understand (Ch. 5.3). I'm going to go through the reasoning, ...
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### Justifying that Standard Entropy of a Reaction is a Constant of Temperature

One of the parts in a question I'm trying to solve for an assignment goes like this: A key issue in the Hydrogen Economy is Hydrogen Storage. This can be restored if a substance $X$ can bind to $H_2$....
1 vote
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### How can standard enthalpies of fusion and vaporization add up to that of sublimation when these occur at different temperatures?

In Atkins' Physical Chemistry, the following diagram appears in the chapter on thermochemistry: The definition of standard enthalpy change is also given: The standard state of a substance at a ...
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### Doubt regarding isothermal reversible process- Thermodynamics

Since its a reversible process, I can say $P_{ext}=P_{int}\pm dP$ so now $W_{int}=\int_{V_1}^{V_2} P_{int}dV$ My question is why can't I assume $P_{ext}=P_{int}$ here and take it as a constant ...
79 views

### Why is more work done for a reversible process?

It is said that reversible processes do more work than irreversible ones. A graph as the one below showing an irreversible and reversible isothermal expansion is used to justify this. However, I don'...
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### Dewpoint of water in relation to composition of atmosphere

A couple of colleagues and I were talking about the nature of dewpoints, specifically the dewpoint of water in relation to the chemical composition of the atmosphere in a closed space. If I remember ...
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### What solvents can I use to dissolve Epichlorohydrin rubber and Chloroprene Rubber

I am working with Epichlorohydrin and Chloroprene Rubbers and I would like to cast films of 2 mm at most. The solvents I have in my lab are DMSO, THF, DMF, Acetone, Ethanol and Propylene Carbonate. ...
307 views

### Total Differential of Chemical Potential

I have seen many sources (for example this libretext) cite that the total differential of chemical potential is $$d\mu = V_m dP - S_m dT$$ where $V_m$ is the molar volume and $S_m$ is the molar ...
1 vote
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1 vote
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### Unusual Inconsistencies in Gibbs Free Energy Values at Specific Temperatures in Thermodynamic Simulation

I was using FactSageEdu software to simulate a metal with a composition of 67% titanium (Ti) and 33% aluminum (Al). During the simulation, I encountered an inconsistency in the calculated Gibbs free ...
62 views

### Temperature change in isobaric processes with and without change in number of molecules

Hello I was thinking about two thermodynamics problems and I wanted to get some insights into how to solve them. The first problem was: Suppose we have one mole of ideal gas under constant external ...
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### Closed pressurized water vessel

Suppose we have a closed container not isolated from the external environment so that heat exchanges can occur on the lateral wall (mainly for convection). The water inside is pressurized by a gas (...
1 vote
80 views

### If E° of a Half Cell is based on the chosen reference Electrode (Generally SHE) then how is the equation ΔG°= -nFE° be valid for a Half Cell

For example let us take the reaction: Zn(s) ---> Zn^2+(aq) + 2e^-(aq) ;ΔG°, which we are considering as our half cell And now suppose, by taking the value of E° of SHE(Standard Hydrogen Electrode) ...
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### Temperature change when mixing different ratios of NaOH and H2SO4 solutions [closed]

Under the same conditions, mixing how many ml of 1M $\ce{KOH}$ solution and 0.5M $\ce{H2SO4}$ solutions to form a total volume of 100ml produces a rise in temperature? 1 vote
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### Why is melting spontaneous when the liquid phase is less stable and should have more free energy than the solid phase?

Imagine a 1kg block of ice that has completely melted at room temperature. If melting is a spontaneous reaction, then wouldn't that mean the products (1kg of water) would have less Gibbs free energy ...
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### Does real-world gas phase chemistry use "concentration reaction quotients" (K_c)?

As a theoretical chemist, my entire exposure to reaction quotients and equilibrium constants ($Q$ and $K$) is through thermodynamics ($\Delta G^\ominus = - RT \ln K_{eq}$ and so on). So as I started ...
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### Does the term "vapor pressure" even mean anything in an open system?

I know this type of question has been addressed before, but I believe mine is slightly different and hints at a potential misunderstanding I've had for a long time. I understand the concept of ...
130 views

### Derivation of "activity coefficient form of the Gibbs-Duhem equation"

I'm trying to differentiate the excess Gibbs energy ($G^{ex}$) to get the activity coefficient ($\gamma_k$), which writes: $$\frac{\partial (G^{ex}/RT)}{\partial n_k} = \ln\gamma_k \quad (1)$$ in ...
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### Is the comparison between absolute values of ∆S and ∆H for a given reaction meaningful? [closed]

How do you know if the reaction is dominated by enthalpic or entropic factor? Do you just compare the absolute values of them? If the absolute value of ∆S is bigger than the absolute value of ∆H, can ...
107 views

### Molar heat capacity of water at equilibrium

Molar heat capacity is defined as the heat energy given to one mole of substance to raise its temperature by 1 degree celcius (or 1 Kelvin) Mathematically, $$C_{m} = \frac {q}{n\Delta T}$$ Here's a ...
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### Gibbs Free Energy and dependence on temperature and pressure

So, I have read that change in Gibbs free energy is defined under constant pressure and temperature, i.e $$\Delta G= \Delta H -T \Delta S$$ but for an ideal gas change in entropy of system can be ...
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### How is temperature inside a bomb calorimeter constant?

I've looked around and have been unable to find an answer. When determining molar reaction enthalpy, you first perform the reaction in the steel bomb then measure the temperature change of the water ...
1 vote
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### Why does bond energy not vary with position?

Consider the formation of a hydrogen bond: $$\ce{H + H -> H2}$$ The $\Delta H$ is $\pu{-436 kJ mol-1}$, so we can equally write the equation as: $$\ce{H + H -> H2 + \pu{436 kJ}}$$ But depending ...