Questions tagged [physical-chemistry]

Study of macroscopic and microscopic phenomena in chemical systems in terms of physical laws and concepts [thermodynamics, statistical mechanics, kinetic theory, quantum mechanics...].

167 questions with no upvoted or accepted answers
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293 views

What is the specific source(s) of sliding kinetic friction

In simplistic (K-8) physics classes, it seems to be generally instructed that the friction between two moving surfaces is due to the unevenness of each surface and the microscopic roughness. However, ...
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2answers
823 views

What would be the first compound formed in the early universe?

This may sound like a chemistry problem, but I suspect this would have lot to do with primordial nucleosynthesis. After all physics underlies everything. It is believed that several elements were ...
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0answers
50 views

Concept of polarization in microwave rotational spectroscopy

I am trying to understand the concept of polarization of molecules after they are excited by a microwave pulse. The context is: The complexes are produced in a pulsed supersonic jet expansion of a ...
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0answers
83 views

How did we first discover oxygen exists as $\rm O_2$ and not just $\rm O$?

How did we first discover oxygen exists as $\rm O_2$ and not just $\rm O$ ? (similarly hydrogen as $\rm H_2$ and not $\rm H$) I vaguely remember knowing a story about how the chemical formula of ...
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0answers
36 views

Stability of saturated energy levels

In The Feynman Lectures on Physics, Vol. 3, Section 15-5, there's a discussion of the stability of various benzene ions. It turns out that the ions for which the all the energy levels up to a certain ...
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0answers
140 views

Why are chemical reactions the same at different gravity levels?

Are all chemical reactions the same at a quantum level in different levels of gravity? How does the mass of subatomic particles change atomic behaviour at different gravity, in terms of speed and ...
3
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1answer
228 views

On thermodynamics of spontaneity of the reduction-oxidation chemical reactions

According to the first and second law for a closed system containing different chemicals we have \begin{align} &\delta Q - \delta W = dU = T dS - p dV +\sum_i \mu_i d N_i\\ &\Rightarrow\;\...
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0answers
192 views

What is a covalent bond?

What is a covalent bond, quantum mechanically? How does it hold the two atoms together, and at one point can you qualify the electron as being shated between two atoms, versus feeling attractive ...
3
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1answer
82 views

In chemical compounds, where does the “magic” come from in atomic “magic numbers”?

It is well known that atoms with a full electron shell are more stable, it is one of the first facts taught in a middle school Chemistry course: "An element whose atoms have no electrons outside ...
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1answer
84 views

How much air could an activated charcoal bag or baking soda box actually purify / deodorize?

Someone I know recently bought a set of small stylish and expensive cloth bags (roughly paperback book sized) filled with activated bamboo charcoal, that you place in a room and it purportedly ...
2
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1answer
49 views

Why doesn't lithium form di-lithium crystals? (Calling Mr.Spock)

Hydrogen is in the first column of the periodic table. At STP it is a di-atomic gas. When cooled and/or under pressure it forms a crystalline solid of di-hydrogen molecules. Calculations indicate ...
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46 views

Chemical potential of a reaction

I often see two various forms of the species $i$ chemical potential $\mu_i$ in a chemical reaction, in terms of enthalpy of formation $\Delta h_{f,i}^0$ and standard state entropy $s_i^0$. My ...
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1answer
65 views

Do discrete symmetries in molecules leave statistical “artifacts” like the Equipartition Theorem?

In statistical mechanics we have the equipartition theorem which can derive heat capacity simply from degrees of freedom. For example, diatomic gases have an increase heat capacity of $ \frac{7}{2} N ...
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1answer
61 views

Which superheavy elements have color?

I read that gold is colorful because relativistic effects change electronic energy gaps ($5d$ to $6s$) so that some of them absorb photons in the visible range. This effect is apparently due to ...
2
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0answers
247 views

Are $\Delta G = RT \ln{\frac{Q}{K}}$ and $\Delta S = -\frac{RT\ln{\frac{Q}{K}}-q_p}{T}$ legitimate relations?

While messing around with $\Delta G = \Delta G^\ominus + RT\ln{Q}$ and $\Delta G^\ominus = -RT\ln{K}$, I found this relation: $$\Delta G = RT \ln{\frac{Q}{K}}$$ which helped me clarify how $\Delta G$...
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142 views

Entropy production in non-equilibrium systems: physical interpretation?

I have been learning about entropy production in non-equilibrium systems as developed by Prigogine and others, especially in the context of chemical reactions. I now understand that from the first law ...
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58 views

Thermodynamic Estimation of Flame Temperature

I am trying to create a simulation program for the internals of a solid rocket motor, and I would like to know how you can theoretically predict the burning temperature of a propellant based on the ...
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0answers
77 views

In osmosis, how does chemical potential ever balance out?

Chemical poential is modeled by the equation $\mu_i = \mu_{i,0} + RT\ln x_i$. If you have one side with some $x_i$ of NaCl and another side with pure water separated by a semipermeable membrane ...
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0answers
79 views

Are the $+\leftrightarrow+$ and $-\leftrightarrow-$ methanol rotational transitions dipole-allowed?

I am quite confused about the origin and justification of the rotational selection rules of methanol, and I would appreciate any help or references. As far as I understand, there are three irreducible ...
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1k views

Why human body is not affected on magnetic field?

Electric-current easily cause shock to human body. But magnetic fluxs through human body do-not cause any perceptible change, as-well no invisible-impacts/ health impacts are well-known. We, when hold-...
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0answers
514 views

How to calculate the minimum kinetic energy required by a surface molecule to escape the liquid (during evaporation)?

Evaporation occurs when surface molecules have enough Kinetic Energy to escape the surface of the liquid. Given a certain volume of liquid at a certain temperature, is it possible to determine this ...
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110 views

Why dynamic equilibrium exists?

We know that at equilibrium Gibbs energy is minimum. We also know that at equilibrium both forward and reverse reactions occur simultaneously, and also we know that for a reaction to be spontaneous ...
2
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1answer
89 views

Do antiparticles exhibit different chemical properties?

In my physics class today. My teacher mentioned anti-helium and since I had never heard of anti-atoms (if you get what I mean by that) just antiparticles, this made me think: If we could produce anti-...
2
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77 views

The underlying chemical interactions behind torque

I did some searching around, and didn't find any previous topics that address torque in this specific way -- here goes: Say I just have a plain ol' piece of wood -- relatively long in one axis, so it ...
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252 views

Why is the activation energy of combustion so large compared with regular bonding?

I wanted to know why combustion requires an activation energy and I found this article (see this too). It says that molecular oxygen ground state is a triplet state (according to Hund's rules), and ...
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367 views

Why is the water diamagnetic?

I checked using my permanent magnet that water is diamagnetic. But why is it like that? Does this have any important consequence for life?
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153 views

Given the Pair Correlation Functions for a Multi-component Fluid, is There a Simple Way to Obtain the Helmholtz Free Energy?

I think it may not be possible. Given all the pair correlation functions (e.g. calculated from Ornstein Zernike theory), it seems possible to obtain the internal energy (assuming different species ...
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0answers
243 views

Confusing Chemical potential of mixtures

I feel that there are very few textbook that treat the chemical potential of mixtures in an understandable clear way, which is why I wanted to ask here about certain things? Although I do not have a ...
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60 views

Approach to model solvent in a lattice: e.g. H2O in NaCl

If a lattice contains a solvent, lets say NaCl and water of crystallisation, what is the condition for a solvent molecule to change it's location? From my current point of view I assume that such a ...
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66 views

Electrochemical cell potential - Prigogine book

I'm trying to understand equation 10.2.14 from Prigogine book "Moder thermodynamics": $V=\frac{\tilde{A}}{nF}=\frac{1}{nF}\left(\mu_X^R+\mu_Y^L-\mu_{Xred}^R-\mu_{Yox}^L\right) - \left( \phi^R-\phi^L \...
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0answers
233 views

High Young's Modulus and Tensile Strength of Carbon Nanotubes

I was recently reading about Carbon Nanotubes having extremely high Young's moduli, as well as high Tensile Strength, making them very interesting fibers. However, when I read this I wondered what was ...
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81 views

generation / destruction of fermions by phonons

my Hamiltonian consists of 1D free fermions coupled to a bosonic bath. The interaction is dictated both by scattering terms $H^{scatt}=\sum_{kq}\alpha^S_{kq}c^\dagger_kc_{k+q}X_q+h.c.$ as well as ...
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127 views

Are metal modes mixed with molecular modes during surface enhanced Raman effect?

This question is dedicated to Martin Fleischmann (1927-2012). When a molecule is adsorbed on a metal surface, the Raman scattering amplitude from the molecule is enhanced. According to Wikipedia, the ...
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194 views

Dissipation when the temperature is not constant

Consider a process where some chemical species diffuses from one part of a system (which I'll call $A$) to another ($B$) at a rate $r$ $\text{mol}\cdot \mathrm s^{-1}$. If the system's temperature is ...
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24 views

What exactly does it mean for an element to experimentally violate the Madelung ordering rule?

The Madelung ordering rule says that as you increase the atomic number of a neutral atom, the electron orbitals fill up in order of increasing value of $n+l$, and in increasing order of $n$ within a ...
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2answers
54 views

How does tanning oil increase UV skin damage?

I see many websites claiming oils amplify UV waves. This would only seem possible if thicknesses caused no reflection as in a quarter-wave coating, but that seems hard to believe. So, is it a myth ...
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0answers
36 views

Is the designation “chemical reaction” right for vibrational and electronic excitation of particles?

I'm currently doing my Master's thesis, which focuses on Atmosphere Reentry Thermodynamics and Kinetics. Due to the importance of this work, I would like to use the best terms to describe any ...
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0answers
11 views

Does anyone knows where can I find the phase diagram of oxygen free copper (OFC or OFHC)?

I am having problems with a niobium deposition I made on a substrate. I increased the temperature to 500 degrees celsius and in theory the film should have a better quality. However this wasn't the ...
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0answers
28 views

What Gas Law does one get from a Lennard-Jones Potential

Given a potential, at low density we can approximate high order potentials as a sum of two-particle potentials. Given such an approximation, using a Lennard-Jones 6-12 potential, one can obtain a full ...
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0answers
38 views

Incompatibility between the Bohr-Sommerfeld quantization condition and the Dunham expansion

I'm trying to apply the RKR (Rydberg-Klein-Rees) method which computes the classical turning points, $a(E,J)$ and $b(E,J)$ of a diatomic molecule for a rotational-vibrational energy value E, and ...
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0answers
40 views

Will the refractive index of a electrolyte change when chemical reaction happens?

Since polarization is the reason of refraction, then anything that changes the structure of molecule, atom, or electron will present as a change of reflection. Thus, to my understanding, chemical ...
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25 views

How to properly align my relaxed molecule onto my gold electrode?

the question is described below since it can be considered a chemistry or physics question: How to translate from one plane to another? originally posted on mathematics SE I am trying to get ...
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31 views

Procedure for “reduction” of thermodynamic derivatives in multi-component systems

I am trying to better understand how the "Reduction of Derivatives" (see e.g. Callen Chpt. 7) works in thermodynamics for multi-component systems. All questions are at the bottom. In a closed system, ...
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0answers
14 views

Why don't we use ionized neon for arc jets?

On a typical arc jet there is a cone in the proppelent stream (ammonia or hydrazine) that acts as an anode and the the nozel itself is the cathode. But why don't we use ionized neon as the cathode and ...
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0answers
43 views

Converting a discrete statistical energy distribution to a continuous version

The probability of finding a particle at a particular energy level when energy is considered discrete is according to Boltzmann: $$P(E_j) = \frac{g_j\cdot e^{-\beta E_j}}{\sum_{j=1}^\infty g_j \cdot ...
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36 views

Mathematical Resolution of Overlapping Signals

I would like to take the opinion of physicists (my area is chemistry). During instrumental analysis, the output is a instrument response vs. time. Each peak corresponds to a molecule which is ...
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0answers
42 views

Why hydrogen bond forming has lifetimes on picosecond scale?

According to this Research http://www.kinetics.nsc.ru/mds/downloads/2009_JSC_Naber_Vol_LifeTime.pdf hydrogen bonds are formed and destroyed within a timescale of a few picoseconds. Why hydrogen ...
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2answers
75 views

What is the energy of an atomic orbital?

When we refer to energy of an atomic orbital what is this energy ? is potential energy ? but if is potential energy then shouldn't be considered the whole potential energy of the atom ( potential ...
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0answers
39 views

How to determine symmetry of the system from the term symbol?

I'm studying term symbols. I can derive them mechanically from the electron configuration using the complete table of microstates. Let's consider a typical example - an atomic carbon with the ...
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62 views

Is flame temperature and the temperature above the flame about the same?

This is a practical question that looks not that academic. I'm trying to design an integrated forge that can do heating and forging together. Blacksmiths usually make a forge kiln like Figure 2, as ...