Unanswered Questions
947 questions with no upvoted or accepted answers
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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's ...
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8
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392
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What exactly is an "electron-sponge"?
What exactly an "electron-sponge" [behavior/action/property/system] nickname is, and what makes a material an "electron-sponge" (preferably, quantitatively)?
From what I found, it's typically a ...
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Removal of nickel plating on MgB2 without damaging the boride?
I need to remove a nickel plating of a MgB2 wire without causing damage to the MgB2. I felt that electrolysis is the best method but I do not know what electrolyte to use for this. I also need to coat ...
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Why does entropy increase in reactions that make more molecules?
I used to understand this (more molecules ⇒ more degrees of freedom), but do no longer, because the total number of atoms is conserved, so translational d.o.f. should just be turned into internal d.o....
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Does phosphoric acid remove stainless steel electropolished layer?
Electropolished stainless steel has a high corrosion resistance due to the oxide film that is created during electropolishing. The film mainly consist of chromium(III) oxide.
Phosphoric acid is ...
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Do "pseudo Van der Waals" gases exist?
In college, when deriving the Langmuir isotherm for gas-solid adsorption, the professor proposed a modified version of the Van der Waals state equation, what he called the "pseudo Van der Waals ...
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Correct Definition of Absolute Electrode Potential
I thought absolute electrode potential is Galvani potential difference at the interface. However, it is given by following equation in John Bockris - Modern Electrochemistry (Ref.1): $$ E^M \mathrm{(...
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Why is the reverse aldol cleavage of fructose 1,6-bisphosphate highly endergonic under standard conditions?
I have another question similar to this one. I just don't have intuition for why reactions are thermodynamically favorable or unfavorable and I'd like to build it. This time I'd like to ask about ...
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1
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Understanding elementary rate laws from a probability stand point
I am learning about chemical kinetics and dynamics and as I understand for a general chemical reaction
$$\ce{aA + bB -> cC + dD} $$ whose reaction rate, r, can be described by an elementary rate ...
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Thermophysical properties of liquid Galden LS 230 between 25 °C and 230 °C
I'm looking for thermophysical properties of Galden LS 230, a liquid polymer (PFPE) produced by Solvay (https://www.solvay.com/en/markets-and-products/featured-products/Galden.html) at temperatures ...
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I found transition states (TS), but calculations aren't supported by experiment. Do I look for more TSs or somewhere else?
I'm using Gaussian to investigate a catalyst system.
Experimental evidence showed that one of three analogues (R = phenyl, Ph), yielded a benzosultam
when treated with 2,4,6-...
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Seeking titanium compound, melting point <1600 °C, decomposes to TiO
The title says it all. I’m new to glass making, and I need a titanium compound that will render me $\ce{TiO}$ through decomposition, and has a melting point under 1600 °C. Hopefully I can get one ...
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6
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How can I compute the temperature change from the de-excitation of excited particle species?
The motivation for the question in the title is that I have some formula given,
$$\Delta T=\frac{3410\ \gamma_{O_2}}{2.5+\gamma_{O_2}},$$
where $\gamma_{O_2}$ is the molar fraction of oxygen in a ...
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1
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How to remove glass shards out of a tiny hole to fit capillary tube?
This is oddly specific, but I am having trouble making the setup work for my electrochemical cell. We're doing Scanning Electrochemical Cell Microscopy (SECCM)* and the device has a capillary tube fit ...
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Dependence of elasticity on temperature and degree of vulcanization of typical commercial rubber band
I am doing a school experiment that tries to find how the elasticity of rubber band depends on temperature.
From all the research I have done, theory suggests stress to increase linearly with ...
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Regarding the standard reduction potential and electrolyte/solid interface
I am modelling lithium-sulfur batteries ($\ce{LiS}$ batteries) and a strange phenomenom happens during charge, named infinite charging, which I show below:
The factor $f_\mathrm{C}$ that appears in ...
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Is there an alternative to potassium iodide as an electrolyte in dye-sensitized solar cells?
I'm helping my son build a dye-sensitized solar cell for his school project according to the directions on homemade-circuits.com. We're currently in the process of gathering the necessary materials. ...
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437
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Is the formation of nitrogen dioxide spontaneous?
I was studying Thermodynamics from my Chemistry textbook (page 181-182, section 6.6 (a)).
I have a question regarding the following text from my book.
Now let us examine the following reactions:
$$\...
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Anomaly in Faraday's constant measurements
I was reading someone's biography, where the writer stated his early interest in Faraday's constant measurements (this is set six decades ago). My understanding was that Faraday constant is a true ...
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Is a change in delta-delta-G typically notated as delta-delta-delta-G?
I'm currently writing a research paper, and need to refer to a difference between $\Delta{\Delta}G$s. The naive way to notate this would be $\Delta{\Delta}{\Delta}G$, but that looks cumbersome and ...
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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 ...
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5
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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 ...
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What are the factors that affect the redox reactions?
In my work, I used $\ce{Co(OH)2}$ and $\ce{Ni(OH)2}$ as an active materials to fabricate as symmetric supercapacitors in which I used 1-butyl-1-methylpyrrolidinium dicyanamide as an electrolyte.
From ...
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966
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Concept of Limiting Current
I am investigating the current output from an electrochemical cell. The electrochemical cell can be broken down into several stages, for example:
Diffusion of reactants across a capillary
Diffusion ...
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432
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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 ...
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113
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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 ...
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305
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Reduction of vanadyl ion
I want to reduce vanadyl to vanadium (III), can somebody please suggest some appropriate methods for it? I am trying to make a redox flow battery for a project but I have only vanadyl sulfate.
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Electrolysis of concentrated sulphuric acid
In my textbook it is given that for electrolysis of dilute sulfuric acid at anode following reactions can occur:
At moderate concentrations
$\ce{2H2O -> O2 + H+ +4 e-}$
And for high ...
5
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1
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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 ...
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What does the equilibrium constant mean for reactions with very small concentrations?
When you calculate the equilibrium constant for a reaction with a higher concentration of reactants, the answer is fairly intuitive. For example, for the reaction:
$$\ce{A + B <=> C}$$
when we ...
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With two reagents common on Mars, fluorite and CO2, how would I produce carbon tetrafluoride?
The hypothetical terraforming of Mars would require the heating of the atmosphere. A commonly suggested method is the in-situ production of fluorocarbons, powerful greenhouse gases.
For example, ...
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Electrolytic reduction of nitrobenzene in differing media
In my lecture notes it is given that in a weakly acidic medium, nitrobenzene on electrolytic reduction gives aniline, which makes sense to me because there is ample H+ in the medium to continue adding ...
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Can you give an example of an electrolytic process that has high Faraday efficiency but low energy effiency
I want a nice example to help illustrate the conceptual difference between these terms to a biologist.
I found this figure which might be helpful.https://www.researchgate.net/publication/...
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How does a silver chloride electrode (Ag/AgCl) convert the potential in aqueous solution to the wire?
I am aware of the redox chemistry that happens at the electrode surface, but I'm not sure how exactly a change in electrical potential in the solution would change the potential in the electrode?
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How to estimate the mobility constant and the surface energy parameter in the Cahn-Hilliard equation?
As a mathematician, I want to simulate phase separations with the Cahn-Hilliard equation
$$
\frac{\partial c}{\partial t} = M \Delta \bigg(\frac{\partial \mu}{\partial c} - \kappa \Delta c \bigg),
$$
...
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445
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Why is the relationship between molar mass and boiling point for alkanes a square root relationship?
I plotted the boiling point of alkanes against their molar mass and found the following trend:
I expected the trend would be linear, since (based on my understanding of what I've learned in class so ...
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4
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1
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366
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Variation of conductance of saturated aqueous solution with temperature
The following question was asked in JEE Mains 2020:
Let $C_{\ce{NaCl}}$ and $C_{\ce{BaSO4}}$ be the conductances (in S) measured for saturated aqueous solutions of $\ce{NaCl}$ and $\ce{BaSO4}$, ...
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Linearity of electrochemical cells and electrical conductivity measurement
I've measured the output signal of a few commercially available conductivity meters and was surprised to see that the signal was typically a square wave of amplitude in the range of 1.5 to 6 Vpp (peak-...
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What is the Gibbs free energy change of physisorption?
In most sites I find online, I see that the Gibbs free energy of adsorption is negative. But, it is also said that physisorption is a reversible adsorption, suggesting that $\delta G=0$ which ...
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Entropy change during electrolysis of water
Consider the electrolysis of water reaction:
$$\ce{H_2O -> H_2 + 1/2O_2}$$
At room temperature and atmospheric pressure, the change in enthalpy of this reaction is $\Delta H = \pu{+286 kJ mol-1}$. ...
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Regarding Ellingham diagrams
In my textbook, the following information is given about Ellingham diagram:
The interpretation of $\ce{\Delta_rG^\circ}$ is based on ${K}$ ($\ce{\Delta G^\circ = -RTlnK}$). Thus it is presumed that ...
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How much energy is required to operate a Sabatier reactor?
I am trying to model some industrial processes and having a hard time finding information about the Sabatier reaction. The Sabatier reaction combines $\ce{CO2}$ (and possibly $\ce{CO}$) with $\ce{H2}$ ...
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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 ...
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Problem interpreting CV diagram in a paper
I am an undergraduate materials science student. I am currently preparing to conduct some research over the summer on alkaline electrolyte membrane fuel cells and have been reading some papers to get ...
4
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1
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249
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Why does the heat of formation of organic radicals and positive ions decrease with their size and degree of branching at the radical or ionic site?
I am currently studying the textbook Mass Spectrometry, third edition, by Jürgen H. Gross. Chapter 2.4.3 Bond Dissociation Energies and Heats of Formation says the following:
The heat of formation ...
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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 ...
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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 ...
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562
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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.
...
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4
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1
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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 ...
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Extrapolating from a calorimetry lab to find a new delta T with different volumes and grams of substance
So, we just finished an AP chem lab where the question was basically:
Given the results of the lab were that $\pu{5 grams}$ of $\ce{CaCl2}$ and $\pu{45ml}$ of water produced a $\pu{13.33 ^\circ C}$ ...
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