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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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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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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400 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+....
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196 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 $\mathrm{...
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23 views

expression of apparent reaction quotient

question When computing the Gibbs energy change of a reaction using Legendre-transformed $\Delta_fG'$ values for a given $\mathrm{pH}$, the formula of the $\Delta_rG'$ of the reaction is: $\Delta_rG' ...
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1answer
50 views

Standard electrode potential of copper disproportionation

I am having some difficulty with the below. It says the standard potential for $\ce{2Cu+ (aq) -> Cu (s) + Cu^2+ (aq)}$ is $\pu{0.36 V}$. The relevant half equations are: $\ce{Cu+ + e- -> Cu}$ (...
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1answer
86 views

Applying Bohr's model for Helium atom

Consider the following atomic model for Helium. Helium contains 2 electrons revolving in circular orbit around the nucleus,in such a way that there is minimum possible repulsion between them.Calculate ...
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49 views

Illustrating moles with sand grains, Are there more moles of SiO2 in a grain than moles of sand on the earth

I have been trying to understand the scale of atoms, thinking about sand grains as an example. With approximately $7.5\times10^{18}$ grains of sand on the earth that is $1.25\times10^{-5}$ moles of ...
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31 views

Reducing pressure and calculation of concentrations at equilibrium

For the equilibrium $$\ce{PCl5(g) <=> PCl3(g) + Cl2(g)}$$ $$ K_c = \pu{4.16E-2 mol dm^{-3}}~\text{at}~\pu{250 °C}$$ $$[\ce{PCl3}] = [\ce{Cl2}] = \pu{0.204 mol dm^{-3}}$$ If the pressure of ...
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28 views

Why isn't the chemistry of a zinc-air battery (meaningfully) hindered by an activation energy barrier?

Virtually every source I've read pertaining to zinc-air batteries explain the chemistry of it either using these formulae or a simplified version of them: $$ \begin{align} &\text{Anode:} &\...
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57 views

Activity of a chemical species and compound

While reading a book on Instrumental analysis by Skoog, in appendix part they explain activity of a species. The relationship between activity of a species and it's molar concentration $[X]$ is given ...
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34 views

Measuring vapour pressure in a closed system

My experiment requires the determination of vapour pressure from which I will calculate the number density (or number of moles of the molecule) later, for a closed system. Here's my setup : Liquid ...
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55 views

What is the precise meaning of “in-phase” (and “out-of-phase”) in this context?

I am currently studying the textbook Infrared and Raman Spectroscopy, 2nd edition, by Peter Larkin. In a section entitled Symmetry: Infrared and Raman Active Vibrations, the author says the following: ...
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55 views

Orbital Approximation

We determined the hydrogen wavefunctions exactly, and the orbital approximation says that we approximate the orbitals of multi-electron atoms with hydrogen wavefunctions. How do we know that this is ...
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24 views

Is the total ionic-dipole bond (hydrogen bonds) acting on an ion stronger than the lattice energy holding the ions together?

When magnesium chloride dissolves in water, its $\Delta H^⦵_\mathrm{sol}$ is negative. Since $\Delta H^⦵_\mathrm{sol} = \Delta H^⦵_\mathrm{hyd} - \Delta H^⦵_\mathrm{latt},$ this means $-\Delta H^⦵_\...
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Boundary conditions in a closed system for diffusion (2nd Fick's law) in a porous medium

I would like to calculate the chloride redistribution in concrete (assumption: porous and homogeneous structure, purely diffusion-controlled mass transfer, closed system). For this I have derived a ...
2
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1answer
105 views

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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191 views

What exactly are the graphs of orbitals?

In my QM class we are finding the wave functions of the hydrogen atom. In spherical coordinates, these wave functions are functions of 3 variables: $r,$ $\theta,$ and $\phi.$ My professor stated that "...
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36 views

Using Maxwell Relations or any other mathematical or thermodynamic relations, prove that (∂Cp/∂P)=−T(∂^2V/∂T^2)

Prove that: $$\left(\frac{\partial Cp}{\partial P}\right)_T = -T \left(\frac{\partial^2 V}{\partial T^2}\right)_P$$ Since $Cp = (\frac{\partial H}{\partial T})_P$ $$\left(\frac{\partial Cp}{\...
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43 views

Why is it experimentally difficult to accurately find the critical volume of a real gas?

I was reading up on the derivation of the values of various critical state functions( $\ce{Vc}$, $\ce{pc}$ and $\ce{Tc}$) from the Van der Waals equation (Physical Chemistry by G.W. Castellan). There, ...
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22 views

Order of Reaction differs in equation and linearisation

I have given the following equation: $A + 2B \rightarrow C$ $ v = –k\cdot [A]\cdot[B]^2$ gives me the orders 1 for A and 2 for B. That results in a total order of the reaction of 3. So far so good. ...
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49 views

Observing bands which I shouldn't be!

I performed the iodine spectrum experiment to observe vibronic transitions. I heated the iodine crystals to produce vapors (at a little above room temperature) and observed absorption spectrum with a ...
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32 views

Competing half reactions in electrolysis of aqueous solution of sodium hydroxide

If you run a direct current using pure nickel electrodes through a solution of NaOH in distilled water, you will separate the water into hydrogen and oxygen. Are there any other reactions that could ...
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21 views

Greater ligand stabilization of the lower oxidation state increasing redox potential

According to Atkins, P.W., De Paula, J. and Keeler, J., 2006, Atkins' Physical Chemistry, $$ \begin{align} \ce{[Fe(CN)6]^3- + e- &<=> [Fe(CN)6]^4-} &\quad E^\circ &= \pu{+0.36 V} \...
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123 views

Why when deriving the Clapeyron equation can you assume that dH = dq, as surely the pressure is not constant?

Part of the Clapeyron equation involves replacing $\Delta S$ with $\Delta H/T$. I can see the step from $\Delta S$ to $\Delta q/T$ but I'm not sure why you can replace $\Delta q$ with $\Delta H$. From ...
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51 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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131 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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176 views

Does the activation energy depend upon the stoichiometric coefficient?

For the decomposition of $\ce{N2O5(g)}$ it is given that $$ \begin{align} \ce{2 N2O5(g) &→ 4 NO2(g) + O2(g)} &\quad\text{activation energy} &= E_\mathrm{a}\\ \ce{N2O5(g) &→ 2 NO2(...
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1k 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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60 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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88 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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65 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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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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53 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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64 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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53 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 ...
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42 views

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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138 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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17 views

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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49 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 ...
2
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1answer
55 views

3D printing of alumina

I want to print a structure of alumina, and the 3D printer that I am using is an extrusion-based printer. So I need your help in knowing that what composition (binders and deflocculant) of alumina ...
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45 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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58 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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60 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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1k 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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0answers
49 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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182 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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146 views

Rotational barrier of biphenyl in ground and excited electronic states

I'm studying how the energy of biphenyl varies with its dihedral angle. I know how to describe the dependence quantitatively, but still, I don't know how to explain why the rotational barrier of ...

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