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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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3
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166
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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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87
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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)
...
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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 ...
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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 $H_2$....
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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 ...
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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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How original is my general matrix formula for rate equations?
I was dissatisfied with the method my teacher taught me to solve rate equations, where you're given experimental values for the concentrations of reactants, and the rate of reaction, which given by
$$...
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Reference for proof of Van der Waals equation coefficient b=4 times molecular volume?
Van der Waals equation coefficient b is approximately 4 times of the sum of the molecular volume. There are different kind of proofs for this. What I am interested in is a very simple one: the centers ...
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Does a chemical reaction depends on the amount of reactants?
A chemical reaction depends on many things like the temperature, pressure etc. i wanted to ask if It also depends on the amount of reactants for example;
If A + B gives C and assuming this equation is ...
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Why is the work done on the system not equal in frame of gas and surroundings?
Consider an isothermal irreversible process for an ideal gas in a cylindrical container closed with a piston (system). Initial and final states are $(P_1,V_1,T)$ and $(P_2,V_2,T)$ respectively. ...
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Why are the latent heat of vaporisation values unavailable for cooking oils?
Oil evaporates. We know this, it's called the "smoke point". So why is it then, that whenever I try to find reference values for the latent heat of vaporisation for cooking oil, such as ...
2
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1
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Does it make any sense to graph 1/T versus ln(Kc)?
I calculated $K_c$ experimentally for the reaction $$\ce{CO2 + H2O -> H2CO3}$$ at different temperatures. Because $\Delta G =-RT\ln(K)$, I thought that graphing 1/T against $\ln(K_c)$ would give me ...
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Is ΔH = ΔU + ΔPV only valid for gases?
In this question, formula ΔH = ΔU + ΔPV is used. In the solution, ΔPV is replaced for RTΔng. As there are solid products also in this equation, don't we consider ΔPV for them. Also if there were ...
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Sign of ∆S in conversion of diamond to graphite
It is said that ∆S is positive as randomness is increasing from diamond to graphite as in diamond molecules are tightly packed together but we know that ∆S=∆H/T for phase transition and that ...
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Confusion regarding spontaneous and non-spontaneous reactions
According to Wikipedia: "A chemical reaction is endergonic when non spontaneous. Thus in this type of reaction the Gibbs free energy increases."
My problem with that statement is the wording ...
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Which Reaction is More Thermodynamically Favourable?
I have a gaseous mixture containing $\ce{CH4}$, $\ce{CO2}$ and $\ce{H2O}$ that is being reformed via the Steam-Methane Reforming Reaction (SMR), the Dry-Reforming of Methane (DR) or a combination of ...
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A general doubt regarding extensive/intensive properties and units in thermodynamics [closed]
I know that for reversible processes: entropy change = dq/t
Here its unit should J/Kelvin but it is mentioned in my books that its unit is J/Mol-Kelvin. I do not understand why there is mole in ...
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Criterion for Spontaneity for Closed Systems at Constant Volume and Pressure
For a closed system at constant temperature and volume, the criterion for spontaneity is $dA < 0$. However, for a system at constant composition, the total differential of $A$ is given by
$$dA = -...
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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. ...
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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 ...
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How to relate zero K to statistical analogue of entropy?
Here we have a common equation of entropy
$$ S = klnW $$
At 0 K we have only one microstate and W is 1, therefore S = 0
Now we can consider another representation of this equation
$$ S = klnQ + \frac{...
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2
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Why does the second law of thermodynamics imply that processes with positive entropy change are spontaneous
My understanding of the second law is that for an isolated system, the entropy change accompanying any process is non-negative and is zero if and only if the process is reversible. I don't see why ...
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How do I approach the problem if Cp is given as a function of volume?
Here is the problem I'm trying to solve:
A system undergoes Isothermal Expansion under the atmosphere. For the system, $ C_p = a + \frac{b}{V} \ $. The process is given by $ P_{ATM}, V_1, T_1 \...
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How to treat enthalpy change and pressure in reactions involving a liquid and solid state
In physical chemistry, it is often stated that "at constant pressure, the change in enthalpy gives the amount of heat transferred into the system" and the justification for this claim is
$$...
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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 ...
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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 (...
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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?
user138000
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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 ...
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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 ...
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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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1
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113
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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 ...
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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 ...
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How does a reduction in potential energy in a chemical bond release energy
This question has to do with the idea of stability and energy. The premise is that systems will tend towards lower energy states, that’s why bonding happens and electrons prefer single orbitals. And ...
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What meaning does Gibbs energy acquire when applied to solutions?
I have been picturing functions like enthalpy and Gibbs free energy as mathematical tools, which were defined in such a way as to be useful for some specific cases. I understood enthalpy as a useful ...
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