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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Perturbation theory for molecules, chromophore group, dipole approximation,

I am interesting in chromophore group and dipole approximation. For example, i have a molecule (acetone or any other ketone/enol) which is belongs to some symmetry group. Because of the symmetry ...
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135 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 ...
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Why do electrocatalysts based on polyoxometalates and carbon materials have a weaker activity/performance in acidic media?

I am testing now some doped N and S doped carbon nanomaterials alone and immobilized in POM for the purpose of developing a nanocomposite that can serve as an electrocatalyst for energy-related ...
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128 views

What is the ANO-RCC basis set and how does it work?

On the basis set exchange, the ANO-RCC basis looks huge, even for hydrogen: ...
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48 views

Defining the partial pressure equilibrium concentration

First off, I am not a chemist. I'm an engineer with an interest in thermodynamics for engine simulation for the basis of emissions. So if I have asked something stupid, this will be why. So I am ...
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43 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 ...
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49 views

What's causing this dip in the FCS curve?

This is a fluorescence correlation spectroscopy measurement of light harvesting complexes. What could be causing the dip at 100 microseconds? Edit: The same thing was observed using fluorescence ...
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39 views

How are second and third electron affinities of atoms measured?

Wikipedia data page on electron affinities shows second and third electron affinities. Of course, they are negative, because one tries to attach electron to anion. But how are they measured or ...
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793 views

Chemistry: What's the difference between “binding energy” and “ionization energy”?

In respect to PhotoElectron Spectroscopy (PES), we are analyzing graphs with "binding energy (MegaJoules)" on the x-axis, and with "relative number of electrons" on the y-axis. I have also seen the x-...
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32 views

Benzophenone Ketyl color origin

I was recently preparing the benzophenone ketyl radical by reacting it with sodium in toluene. Although this compound is really well known and it seems somewhat obvious and accepted in literature that ...
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144 views

How to without calculations understand the liquid-liquid extraction efficiency?

I'm asking myself this question for a very long time and I haven't found a simple an good explanation yet for the fact that it's better (if you want to clean them) to wash your hands two times with ...
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103 views

Hückel method for biphenyl

I am trying to calculate the energy levels of biphenyl (see picture below) using Hückel method. Since this is my first time using Hückel I am a little confused. Biphenyl has 12 carbon atoms, ...
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60 views

Ionization energy in Geiger counters

Geiger counters can detect radioactivity because nuclear radiation consists of particles or radiation of sufficiently high energy to eject electrons from atoms. Consequently, this type of radiation is ...
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165 views

Generalized reaction rate and derivation

Most textbooks give the reaction rate $$r = k C_\ce{A}^a C_\ce{B}^b \tag{1}$$ for the elementary process $\ce{a A + b B -> P}$. However, expression (1) is not valid in the general case: e.g. it ...
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33 views

Does MEK-toluene system create a negative deviation from Raoult's law?

From the experimental data obtained in our lab, when pressure is plotted against mol fraction and partial pressure, it exhibits a negative deviation from Raoult's law which must mean that the forces ...
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108 views

Non-ideal velocity distribution of gases

A recent question about the velocity distribution of ideal gas molecules got me wondering. How much would the velocity distribution vary for non-ideal gases? I was wondering about a mixture of ...
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319 views

Ethanol Water mixture viscosity

It is found that increasing composition of $Ethanol$ in $Ethanol$-$water$ mixture increases the viscosity of the mixture upto certain composition, but after that the viscosity begins to decrease again....
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262 views

Calculate work done by burning benzoic acid exposed to the free air

I'm self-studying and can't solve this problem in Ball's Physical Chemistry. Now, the errata shows that the answer in the book is not correct; still, I can not make sense of it. $(2.55)$ Benzoic ...
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64 views

Can the friction of air disintegrate objects if they are accelerated enough?

Can an object be thrown so fast that the individual atoms or molecules separate in air? I mean if you could accelerate an object fast enough, would it disintegrate from the friction of air? If so, ...
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109 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 ...
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2answers
329 views

Given this liquid-liquid phase diagram, is the green line the nitrobenzene-rich phase?

The temperature-composition diagram for hexane and nitrobenzene at 1atm. The region below the curve corresponds to the compositions and temperatures at which the liquids form two phases. The upper ...
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42 views

Why there are just two Ramachandran angles in protein structure for two peptide bonds?

I really want to understand why there are just two ramachandran angles to understand the structure of the protein and why not three or many ? Can someone suggest some reference and explain this ?
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439 views

Magnetic work and the first law of thermodynamics

We commonly encounter the first law of thermodynamics in the form $\mathrm{d}E = T\mathrm{d}S - p\mathrm{d}V + \mu\mathrm{d}N$, which notes the contribution of thermal, pressure-volume, and chemical ...
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131 views

pH of amphiprotic species

I was asked to find the pH of a diprotic species $\ce{BHA}$ where $B$ is the cation and $\ce{HA}$ is the anion given the first and second dissociation constant of acid $\ce{H_2A}$ and the base ...
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53 views

Could UV lasers be used to split CO2 and H2O?

I was wondering whether intense UV light, tuned to the correct wavelength, could be used to split carbon dioxide and water molecules as a first step towards synthesizing liquid fuels.
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363 views

Predict polarity (TLC, column) using ChemSketch (-Draw)

I'm currently working on a project where I have to make and isolate often quite similar molecules. But, as I change the functional groups the overall electronic situation and polarity of the product ...
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80 views

What would happen if the volume changes in first order reactions?

I am searching for any piece of hints but couldn't find out anything What would happen if the volume changes in first order reaction? For example, suppose there is a first order reaction of ideal ...
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40 views

Looking for a pressure phase diagram of selenium at large ranges of pressure and temperature

I'm doing undergraduate research and our group is having a lot of difficulty finding a comprehensive pressure phase diagram or phase table for selenium (including most known packing geometries that ...
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32 views

Should the coupling between vibrational modes increase or decrease with increasing temperature/vibrational energy level?

At low temperatures, the amplitude of vibrations should be smaller, so the vibrations should be as harmonic as they are ever going to be. Thus, the normal mode description of vibrations should be at ...
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102 views

Heat capacity of mixtures is higher than their pure contituents?

I'm currently studying the effects of how changing mixed-refrigerant compositions effects their heat capacity. Surprisingly, my data suggests that some combinations of mixed-refrigerants have heat ...
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497 views

Relative Humidity, vapor pressure, partial pressure

The partial pressure of water in the mixture is the equilibrium vapour pressure of water at the temperature specified. Relative humidity (RH) is the ratio of the partial pressure of water vapor to ...
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69 views

What substance would crawl out of a vessel?

I remember in my first chemistry lessons at high school my teacher told us about atomic properties of materials elastics and stiffness and what ever else. At one point he came up with an example of an ...
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182 views

Alkali metals and viscosity

I've recently conducted a viscosity experiment to find the relationship between alkali metal ions, the concetration of the solution, and the viscosity of the solution. We used the Oswald viscometer to ...
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42 views

How to determine concentration limits of a buffer that's limited by solubility?

I need to maintain a certain range of % of ionisation from a buffer. For e.g. Histidine buffer. When making high concentration of this buffer at (say) pH 7.2, 25'C, [concentration] is limited to 75mM ...
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38 views

Extimating the repartition of water between hygroscopic compounds

Sulfuric acid is sometimes used as a drying agent. According to literature, one possible application is, for instance, in the drying of bromine. Some questions came to my mind: which concentration ...
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20 views

Comparison of ways to provide energy to a reaction

As we all know, you can provide energy to a reaction to overcome the activation energy of a reaction by heating the reaction. I have, however, recently sat through a talk where someone 'powered' a ...
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150 views

Physical Chemistry: Calculating ΔG, ΔH, ΔS on a given equation

This question was brought in class, but I have no clue if my answer is correct or not. I wonder if you guys can double check my answer. Between $\pu{0 ^\circ C}$ and $90 ^\circ C$, the potential ...
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2k views

Finding the rate constant of a first order reaction

The reaction $\ce{A + B -> AB}$ is 1st order with respect to A and zero order with respect to B. The reaction is begun with the initial concentration of both reactants at $0.100 \,\text{...
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473 views

What is the need for dipole moment if electronegativity already exists?

Say we have an HCl molecule. The difference in electronegativities of the H and Cl atoms tells us how polar the HCl molecule is. The dipole moment is also a measure of the degree of polarity in ...
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129 views

pH calculation in case of amphiprotic ion

$100\ \pu{ml}$ of $0.1\ \pu{M}\ \ce{H3PO4}$ is titrated with $0.5\ \pu{M}\ \ce{NaOH}$ solution till 2nd equivalence point. Then resultant solution was mixed with $10\ \pu{ml}$ of $0.5\ \pu{M}\ \ce{HCl}...
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86 views

rate constant via flux-flux correlation function for linear potential energy surface

How does one calculate fully quantum mechanical rate ($\kappa$) in the golden-rule approximation for two linear potential energy surfaces? Attempt: Miller (83) proposes $\kappa=\int{Tr[\exp{(-\beta\...
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88 views

Chemical theory, formula(s) that predict final *volume* of a solution?

I asked this question a couple years back regarding the volume of a mixture being less than the volume of the original solute and solvent, but this question asks if there is theory and/or formulation ...
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63 views

Does the frequency of incident light change in Beer-Lambert Law?

The Beer-Lambert law is meant to describe the interaction between a solute and incident light. But, does the frequency of the light here change due to the interaction with molecules? I think there ...
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353 views

Aluminum powder reaction with air

I have made aluminum powder in a ball mill a few times, but my last batch began to smoke and caught fire soon after I poured it from the tumbler. Nothing unusual was afoot. It was poured into a paper ...
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184 views

How to determine the permissible values for which solution of the Schrödinger's wave equation exists?

My textbook( A Textbook of Physical Chemistry, Dr. O.P. Tandon ) says that solution of the Schrödinger's wave equation exists only for certain permissible values which are called eigen values.( ...
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144 views

Are molecules on surface of liquid stationary due to surface tension

Are the molecules which are on the surface of a liquid ie the molecules on the top film stationary ie not move about each other under steady conditions ie unlike molecules in the bulk because of ...
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199 views

determination of glucose syrup in sugar product

I work with a sugar product that contains saccharose (approx. 70 %), glucose syrup (approx. 15 %), glycerine (approx. 3 %) and some other ingedrients, e.g. water. Glucose syrup consists of 5 % glucose ...
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350 views

NAMD free energy calculations (FEP, Alchemical)

I am trying to calculate the absolute free energy of a protein-ligand-complex using the free energy perturbation theory. Following the alchemical route in this tutorial, I have calculated eight MD-...
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583 views

Problems with Daniell cell

In Zemansky and Dittman's book on thermodynamics, pages 41–43, the authors discuss the Daniell cell as a thermodynamic system. Their cell consists of two saturated $\ce{CuSO4}$ and $\ce{ZnSO4}$ ...
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593 views

Why is the degree of dissociation for a weak acid α, but for a weak base, it's 1−α?

From the equation used in this answer: Calculating charge on amino acid from pKa $$\alpha=\frac{1}{10^{\mathrm pK_\mathrm a-\mathrm{pH}}+1}$$ Degree of dissociation of weak acid is $\alpha$. However,...