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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...].

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39 views

Question about decay

So, I already asked a question on the topic, that helped me understand some more. Now, here i find myself blocked again. I don't know how to solve the following problem: In a basement, you notice ...
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37 views

Activity and radioactive decay

So, I am pretty new to that concept, which i am learning about in the context of physical chemistry. I am a mathematician, so a physicists approach can be confusing at times. I have two questions : ...
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52 views

Can 2 atoms of oxygen be transformed into $H_2O$ using electicity? [closed]

I am writing a novel in which a scientist is required to design a self sufficient moon base and was hoping to use this idea and whilst I have created a model where this is possible I would like to ...
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16 views

Gas Transport Problem

I have a question that I thought would be a very simple effusion calculation that sent me down a massive rabbit hole after I tried to look it up in Landau's Physical Kinetics and so now I'm coming to ...
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1answer
27 views

Why can't adiabatic changes decrease entropy for a closed system?

I read that adiabatic changes in a closed system can never decrease the entropy. To try to understand why, I thought of two scenerios: reversible processes, and irreversible processes. For a ...
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14 views

Does a static-firing rocket engine do work?

Is the "working fluid" doing any work during a static-fire of a rocket engine. Since the rocket is held stationary, there is no work being done on the rocket right? However, is the exhaust doing work ...
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24 views

Confusion about internal energy and temperature during a phase change

During a phase change, internal energy of a system will change because energy must be added or subtracted (depending on "direction" of change) from the system in the form of latent heat. However, the ...
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1answer
47 views

$H_2O$ vs $2H^+ +O^{2-}$

I am wondering the mass deficit between 2*H + O and H2O. I.e. if I would know the accurate mass of one atom of hydrogen on it's own and the mass of one atom of oxygen on it's own how much of a ...
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2answers
48 views

Arriving at the definition and purpose of enthalpy

I've been trying to understand the conceptual idea and purpose of enthalpy for the past two days. From what I've learned, enthalpy is defined as: $$E = U + PV$$ This leads me to my first question. ...
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14 views

On diagonal terms in the Coulomb matrix

I have seen many machine learning algorithms for prediction of quantum chemistry properties that use Coulomb matrix as their input. Coulomb matrix is defined as $$\boldsymbol{M}_{i j}^{\mathrm{...
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1answer
143 views

Why does entropy allow heat to be converted to work?

Physical chemistry has made me question everything. Recently, I was thinking: "why is it even possible to convert heat to work?" From what I learned, a heat engine can take energy in and convert it ...
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17 views

$H_2O$ dissociation by ionization in a discharge tube

As a casual amateur scientist, I wonder if it is efficient to electrolyse water in a discharge tube. I imagine that there would be 4 electrodes arranged perpendicularly. the first set of electrodes ...
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9 views

Calculating Simple Ground State Energy Of Hydrogen From Geminal Spin Function

I'm very new to quantum stuff and I'm experimenting, but I'd like a good explanation here if you can give it. Here's the circuit diagram and the results. I'm seeing from this paper that you can get ...
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25 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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1answer
23 views

Details of forces involved in osmosis at a microscopic level

Well I read about osmosis from different sources and most of the chemistry books did not delve into intricate details so I consulted many sites to get the physics approach to osmosis and they mostly ...
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2answers
60 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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14 views

Conservative or non conservative convection

I want to describe the convection of a species $B$ by another species $A$. Meaning that $A$ is bringing $B$ with it, and there is no other velocity associated to $B$. So I have 2 conservation ...
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9 views

What is the difference between laminar burning velocity and laminar flame speed?

I am trying to understand the difference between laminar flame speed and laminar burning velocity for a flat flame without heatloss and stretch effects. Please help me with this question.
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1answer
41 views

Diamagnetism question

I have a question why are some elements regarded as Diamagnetic despite having unpaired electrons, for example Sulfur leaves 2 unpaired electrons yet it's considered diamagnetic, you would think it's ...
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2answers
46 views

Why does pressure seem to be an extensive variable considering Dalton's law?

I learned that in thermodynamics, pressure is regarded as an intensive variable, while properties that you can add up such as mass or volume, are considered extensive. However, to me, Dalton's law ...
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1answer
43 views

Cerium 140 into Cerium 141 via use of ceria powder?

I was reading a PDF Cerium 141 production, that stated cerium 141 productions via ceria powder. My question is how is the Cerium 141 actually created via using standard ceria powder?
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1answer
77 views

Would deuterium or tritium be a better rocket fuel? [closed]

Im not that scientifically literate but through my basics as hell understanding of chemistry is that denser=better wouldn't the denser forms of hydrogen be better for fuel since they would weigh ...
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1answer
44 views

How to convert $\rm kg/m^3$ to $\rm J/m^3$ for natural gas and biogas? [closed]

I want to convert from mass density to energy density: Natural gas has a density of $0.8\: \rm kg/m^3$. Biogas has $1.15\:\rm kg/m^3$. I want to convert them into $\rm J/m^3$ so that I can ...
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1answer
55 views

Definition of electron density in DFT

I read that the electron density used for density functional theory in a system of $N$ electrons with wavefunction $\psi$ is defined as $$\rho(r)=N\int d^3r_2\dots d^3r_N \psi^*(r,r_2,\dots r_N)\psi(...
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29 views

What is the static exchange approximation?

In this paper, on the 4th page (and throughout), they talk about studying electron-helium scattering in the "static-exchange approximation". I have scoured the literature and have not been able to ...
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1answer
44 views

Increase the surface tension of polypropylene

I'm working on a project and I need to increase the surface energy of polypropylene. I want you to tell me a way in order to increase surface energy of polypropylene?
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1answer
22 views

Shouldn't the remaining photon energy be transferred to both electron and ion in a photoionisation?

I'm studying photoionisation and photodissociation, and I'm having a hard time trying know the microscopic details of such processes. I've read that in a photoionisation the photon is absorbed by a ...
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1answer
78 views

Solution Cahn-Hilliard 1d for a domain of finite size

I'm trying to get the solution of the Cahn-Hilliard equation in 1d with a certain mass $C$. We have two components, and let's assume we have the relation $c_1+c_2=1$.Hence we take only the variable $c=...
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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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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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2answers
199 views

Why are helium and lithium so different, while lithium and beryllium are similar?

How is it possible that helium, having 2 protons, and lithium, having 3 protons, are so different in terms of their physical properties? How come one is a gas at room temperature and the other is a ...
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2answers
42 views

Why we assume additivity of internal energy in thermodynamics when we can have chemical reaction

In the usual formalism of thermodynamics, the internal energy of system is said to be extensive in a sense that if we construct n identical copies of same system, the energy of the composite system ...
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1answer
48 views

My soap produces less lather as it gets old

I don't know it you have encountered this too but I have observed this "phenomenon" from the last few hundred soaps I have used. As the soaps get older they produce less lather than they produced ...
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3answers
67 views

$CO_2$ heating experiment (high school)

A student is trying to run some experiments for a project to explore how the concentration of CO2 affects the temperature of air. For this, she: Drops different ammounts of dry ice (between 0 and 2....
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20 views

Chemical reactions in fluids

The equations of motion of ordinary relativistic hydrodynamics are derived by considering conservation equations of the energy tensor and particle number current, where constitutive relations relate ...
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22 views

Relation between oscillator strengths $\log{gf}$ and the Einstein $A$-coefficient, rotational quantum number, …

I'm analyzing the spectra of M dwarfs. Some authors characterize the lines with the oscillator strengths $\log{gf}$ while others follow different paths with the Einstein $A$-coefficient. I would like ...
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10 views

Entropic Restrictions to Water Interfaced with Hydrophobic Molecules

The occlusion of hydrophobic molecules from polar solvent such as water, I have read, is an entropic effect. My question is pretty simple -- at an interface of water and oil, or in the clathrate cage ...
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30 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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1answer
46 views

Increasing the melting point of metal

I need to know how one can increase the melting point of a metals like steel, tungsten or ... about 500 degrees and without destroying its shape?
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4answers
2k views

Does a proton have a binding energy?

When calculating the $Q$-value, $Q = \Delta M \cdot c^2$, of this reaction: $$ ^6Li \ (\alpha, p)\ ^9Be \quad \iff \quad \alpha + \ ^6Li \ \longrightarrow \ ^9Be + p $$ The $Q$-value can also be ...
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1answer
70 views

Why is detailed balance required for thermodynamic consistency?

why does the Wegscheider condition or detailed balance have to be true for chemical reactions and what does it mean to violate it in terms of thermodynamics? here is an attempt to derive a simple ...
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4answers
102 views

Dimensional analysis with derivatives, logs, exponents and trigonometric functions

How should we do dimensional analysis when we have derivatives, logs, exponents and trigonometric functions in an equation. Should we assume that the operands are pure dimensionless numbers? Coming ...
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4answers
178 views

Does freezing point depression also affect the speed at which something melts?

If you have a pure water frozen, then it should begin to melt if you apply 33°F air to it. If you have impure water that's frozen, it's melting temperature might have dropped to 30°F. If you apply ...
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1answer
86 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 ...
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1answer
67 views

Where is the extra heating value of coal compared to the original wood coming from?

My question is about the formation of coal seeming to break the laws of the conservation of energy (that energy can neither be created nor destroyed but instead transferred from one thing to another). ...
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68 views

Why don’t ALL polymers collapse even when their compact state would clearly be favoured in terms of having a lower Helmholtz free energy?

This question is based on example 8.3 in Molecular Driving Forces, Dill and Bromberg (https://books.google.ch/books?id=1gYPBAAAQBAJ&pg=PA136&lpg=PA136&dq=polymer+collapse+a+toy+model&...
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68 views

Reference for the electronic levels of the nitrogen atoms resulting from the dissociation of the nitrogen molecule

I would like to know a book or paper that makes a detailed description of the electronic levels of the nitrogen atoms, N+N, resulting from the dissociation of the nitrogen molecule, N$_2$, also at a ...
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1answer
86 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
43 views

If we need the term/concept of “isotope”, or why we call them “elements” of the periodic table

I just read this: A nuclide is a species of an atom with a specific number of protons and neutrons in the nucleus, for example carbon-13 with 6 protons and 7 neutrons. The nuclide concept (...
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6answers
13k views

How is water heavier than petrol, even though its molecular weight is less than petrol?

Molecular weight of petrol is so much higher than water, but when it comes to physical property, weight, one litre of water weighs more than one litre of petrol. How is it possible?