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Questions tagged [physical-chemistry]

The study of chemical systems using the laws and concepts of physics. This usually requires the techniques of thermodynamics, statistical mechanics and quantum mechanics.

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Rate of cathodic reaction vs Tafel slope

One of my reference engineering books says that for the cathodic protection process (in seawater): Al $\rightarrow$ Al$^{3+}$ + $3e^-$ (anode, setting the protection potential at about -900 mV SCE) ...
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53 views

Why can we know a materials properties by knowing its ground state at 0K - DFT

I have had this doubt ever since I was introduced to DFT. For what I gathered whatever results you obtained with DFT (by using VASP, quantum expresso or any other software) you can say those ...
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149 views

Oscillator strength of a transition

I am trying to compute the oscillator strength in a molecule. Therefore I've got its Energy level values plus both wave functions $\Psi_i$ and $\Psi_j$ for the transition I want to calculate the ...
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77 views

Calculating excitation energies of a molecule

I am trying to calculate the excitation energies for the first three transitions of a molecule which is made up by a chain of k phenyl rings, where k shall be between 1 and 8. The angle between each ...
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108 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 ...
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56 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 ...
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148 views

Is this a viable method for graphene production?

In a cup of warm water add sugar until it no longer dissolves then add a few spoonfuls more of sugar. Drop in a small amount of graphite powder into the sugar water mixture. Stir it up well. There ...
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51 views

The difference between bonding and unpaired single electron radicals

I was wondering as to why would two unpaired single electron radicals form a bond. So, I tried to compute the added ground state energies of two particles in two distinct, yet identical boxes, The ...
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1k views

What's the actual difference between Formality and Molarity?

Today, I came across a question: "State the differences, in not less than 5 points, between Formality and Molarity". Using my knowledge, I wrote down 2 points, and stretched it to 3 somehow, but that'...
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49 views

How to effectively induce the bending motion of carbon dioxide?

I would like to know how to effectively induce the bending motion of $\ce{CO_2}$ with femtosecond IR lasers. In other words, how to effectively populate bending vibrational states in $\ce{CO_2}$ ...
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2k views

Effect of temperature and pressure on structure of solids

What is the effect of these conditions on the structure of solids? My book has the answer that confuses me. I got nothing about it. Can you please explain? The answer of the book is With the ...
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164 views

How does the rate determining step determine the overall speed of the reaction if it is the first step in the reaction?

I can imagine it determining the rate of the whole reaction if it is the last step since that means that we will have lots of the reactants needed for the rate determining step, synthesized in earlier ...
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101 views

Supercritical fluids polarity

Water is a polar solvent, but in the supercritical fluid state, it is much less polar, I presume because of the cleavage of hydrogen bonds. On the other hand, carbon dioxide is non-polar, but as a ...
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247 views

Enthalpy change of chromate-dichromate reaction

I am a uni study doing chemistry. I have taken a little bit in highschool before, but not in a while. In a (nonassessed) practical, we have to predict how heating a chromate/dichromate solution: $$\...
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92 views

How/where can I find a reliable atomic radii table?

I am currently working on a periodic table to include it in a experimental chemistry book and I would like to include non-bonded atomic radii data so it would be easier for the students to learn about ...
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107 views

Is there a physical explanation behind the derivation of spectroscopic term symbols?

In deriving the spectroscopic term symbols, one method seems common among several sources, the clearest presentation for me being located here, a derivation of the term symbols for a $d^2$ ion. So, ...
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84 views

What are the disadvantages of using the InChI format?

What are the disadvantages (if any) in producing and using the InChI format of chemical compound representation in chemoinformatics? Are there any particular problem one can face when using InChI?
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416 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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1answer
210 views

Is the following rate law possible for the given reaction?

A researcher is investigating the following overall reaction: $$\ce{2C + D -> E}$$ The researcher claims the rate law for the reaction is written as follows: $\text{Rate} = k[\ce{C}][\ce{...
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428 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 ...
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271 views

Negative hyperconjugation stabilizes tricyclopentane derivate

As far as I know, negative hyperconjugation means, that we have electrons that are transferred from a p- or $\pi$- to a $\sigma^*$-orbital. In the lecture, we analyzed a TMS-substituted ...
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638 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 $\pu{1 bar}$...
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421 views

How to calculate the radius of gyration (Rg) and the molar mass from light scattering data (Rθ and θ/degree)?

I have a homework problem that I don’t have a solution for, so I would like understand how to solve it and to know if my suggested way of solving it is on the right track. The problem is as following: ...
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92 views

How could I find the solubility of hydrocarbons such as iso- and n-Butane in liquid Methane?

I am trying to figure out the dissolution capacity of iso and normal butane in methane at very low temperatures (110K). This would allow me to make compositions that prevent freeze out of these ...
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91 views

What closure relations can we use in molecular modelling?

Following my question here about the BBGKY hierarchy I was wondering does anyone have any experience in using the method outlined. In particular how would I take an equation off the page and for some ...
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278 views

Spectral reflectance identification of types of iron rust

Based on the Wikipedia page about rust, there are red and green types of rust that occur on iron. Red rust is the reaction with oxygen and water and the green with chlorine (in oxygen poor ...
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282 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 $r$...
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250 views

How to store distilled water without introducing impurities?

How can I store distilled water without introducing impurities? I'm going to be doing so electrical studies of pure water and ice and I need a way of keeping the water pure during the experiments. ...
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1k views

Purity of precipitate in selective precipitation

An aqueous effluent contains $12\ \mathrm{mol\ l^{-1}}$ $\ce{Cd^2+}$ and $10\ \mathrm{mol\ l^{-1}}$ $\ce{Mg^2+}$ as solution of nitrates. Current practice is use $\ce{NaOH}$ to selectively precipitate ...
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1answer
67 views

Which solvent is good for using SU-8 particle in Optical tweezers?

I'm studying Optical tweezers. I've used Polystyrene for samples. Nowadays, I've got SU-8 pillar. I wanna use that for sample, but its density is heavier than water. I can't use that. So I wanna know ...
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40 views

Does product induced poisoning qualify as a rate limiting step?

I have a question about whether a particular situation qualifies as a rate limiting step. I have a catalyst that under normal conditions gets poisoned when products accumulate on the catalyst surface. ...
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2k views

What is the formula for migration rate of DNA in agarose gel electrophoresis?

Let's consider a typical agarose gel electrophoresis experiment. An appropriate quantity (not so much that it is overloaded, but not so little that it cannot be visualized) of linear DNA pieces with ...
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26 views

Dissolving Time Function for Concrete

So I was just exploring some ideas on my own and am having trouble analytically solving the following: Let $D(n,m,T)$ be the time it takes to dissolve an n x n x n cube of concrete in m molar HcL at ...
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54 views

Other than heating, is there any evidence that normal RF radiation (say, microwave range) can affect chemical reactions?

There's been a lot written (and debunked) about alleged biological effects from RF radiation, even when it's too low powered to cause heating effects or ionization. Is there any chemical reason to ...
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380 views

How will the transference number of H+ ion in a dilute solution vary as temperature increases?

I know that transference number depends on Ionic mobility, which depends on temperature. But is there any equation which describes the relation of Transference number and temperature, any ions like H+....
3
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1answer
173 views

Finding concentration and moles given final and initial pH

Questions: How many moles of $\ce{NaOH}$ are needed to change $500~\mathrm{L}$ of solution with $\mathrm{pH}\ 2$ to $\mathrm{pH}\ 11$? A swimming pool contains 2 million litres of water at $\...
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26 views

Properties that probe electron kinetic energy

This post is inspired by a question regarding the meaning of off-diagonal elements of the KE matrix (in some AO basis). One answer suggests that a diagonalized KE matrix might not be very useful. I ...
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48 views

Explosive reaction based on reaction rate

Question We have the following chemical reactions: $$ \begin{align} \ce{A + B^* &-> C + D^*}\tag{1}\\ \ce{D^* &-> B^* + B^*}\tag{2}\\ \ce{B^* &-> B}\tag{3} \end{align} $$ ...
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85 views

Why can't calorimetry be used to measure fast reactions?

As my previous post was a bit unclear and unspecific, I am reformulating it. First of all this is a question that I had while reading some concepts my book introduces, so this isn't a homework ...
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69 views

What is the largest known zero-point energy for a molecule?

I was surprised to find out that the zero-point energy (ZPE) for the ground state of $\ce{BH3}$ is a few thousand $\pu{cm-1}$, because for molecules I usually work with, it's much smaller. Does anyone ...
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46 views

Explain why can't zinc be plated out from a Zn(II) solution using standard reduction potentials

I am currently learning about electrochemistry using Zumdahl's Chemistry [1, pp. 709–710]. One of the critical thinking questions is Why can $\ce{Zn}$ not be plated out from an aqueous solution of $...
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50 views

Why will A atoms diffuse from β phase to α phase and B atoms from α phase to β phase?

At the initial compositions 1 and 2 of $α$ and $β$ respectively the chemical potentials of A and B atoms in each phase can be found by extrapolation of the tangents to the free energy curves at 1 and ...
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53 views

Are there any gases that can not be turned into liquid, or liquids that can not be frozen solid?

My son points out that some solids can not be melted (because they combust, for example). He wonders if there are any liquids that can not be frozen, or gases that can not be liquified.
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48 views

How to calculate the value of heat absorption/ heat release during water electrolysis?

The overall reactions with the enthalpies of water electrolysis at room temperature can be represented by the equation below: $$\ce{2H2O + \pu{237.2 kJ mol-1} + \pu{48.6 kJ mol-1} → 2 H2 + O2}$$ ...
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1answer
55 views

Confusion regarding calculating the pH of a salt of weak acid and weak base

I need to calculate the $\mathrm{pH}$ of a salt of weak acid and weak base in an aqueous solution. Method I used for calculation For a salt of weak acid and weak base (assuming complete dissociation ...
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39 views

Are there any surface treatments that would make calcium usable for metallurgy?

Calcium is the best conductor for its weight, but the soluble powdery oxide makes it impractical for use in power lines. Are there any surface treatments or alloying processes that could help? (...
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0answers
36 views

What kind of chemical reaction happens when combining Tahini and Date syrup?

While both Tahini and Date syrup are quite thin, when mixed together they form a paste-like substance that is very delicious, and quite thick. But what kind of chemical reaction leads to such sudden ...
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0answers
30 views

Why different Asbestos types are hydrophobic and hydrophilic

I was doing research into the structure of asbestos to see that white asbestos chrysotile is hydrophilic where as both brown and blue asbestos is hydrophobic. Could you please explain why this is?
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2answers
197 views

Find the pH of an amphiprotic salt dissolved in water at room temperature

Let's say I have a polyprotic acid $\ce{H2A}$ with the following properties: $$ \begin{align} \ce{H2A &<=> HA- + H+} & K_1 &= 1\cdot 10^{-1}\\ \ce{HA- &<=> A^2-+ H+} & ...
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45 views

How to obtain spectroscopic constants Omega_e, Alpha_e, B_e, D_e and D_0 from centrifugal constants?

I need to compute a spectroscopic constants of $N_2^+$ states and I would like to do it using LEVEL16 software, due to its high interpolation flexibility. But it seems, that LEVEL16 can only compute ...