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...].

Filter by
Sorted by
Tagged with
0
votes
0answers
17 views

reverse osmosis membrane

We are second year cram schoolers , we are currently working on a project tackling water desalination by reverse osmosis and are required to do an experience. During the process, we encountered some ...
0
votes
0answers
10 views

What is the behaviour of excited state spins in an intermolecular context?

This question is about luminescence. UV excited molecules can relax emitting light or by vibrations. The relaxation process can occur fast if there is spin conservation between the excited and ground ...
0
votes
0answers
19 views

What causes ${\rm Si}$ to expand when lithiated?

Looking at research into Si-based lithium-ion batteries, the main issue seems to be that the Si increases size by a factor of 4 when lithiated. I'm interested in understanding what actual forces are ...
1
vote
1answer
33 views

Can a quadrupole form in a purely organic crystalline material?

I'm a chemist so bear with me here. This is a question about small molecules, such as biphenyls. In the solid-state biaromatic systems without steric hinderance forms planar conjugated structures. By ...
1
vote
2answers
54 views

Do emission and absorption lines complete each other

If you look at the spectral lines of hydrogen, the emission lines seem to be in the exact same spot where the absorption spectrum is black. Together, they build a full spectrum of visible light. Does ...
0
votes
2answers
56 views

Is it the Coulomb force which acts between electron and protons creating chemical bonds?

When calculating forces on the atomic level, although Quantum mechanics makes the positions of charged particles"smeared out" is it the Coulomb force which is acting between smeared out electrons and ...
-1
votes
2answers
55 views

What will happen if you fired a gun in a room filled with hydrogen gas? [closed]

Will the room explode? How does it happen?
0
votes
2answers
89 views

Why doesn't NASA try using high-explosives to fuel rockets?

For a smoothly burning liquid-vapor mixture, I understand that burning hydrogen and oxygen is the best possible solution, not just for now but even theoretically. (?) But I read about ideas, that ...
0
votes
1answer
52 views

On an atomic level is energy only transferred through phonons and photons?

On an atomic level is energy only transferred through phonons and photons - there's no other means atoms can absorb or give off energy & all chemical phenomena & physical transitions arise ...
0
votes
1answer
41 views

When is energy transferred to/from atoms mechanically (vibration, rotation) vs photons?

In reading intro quantum mechanics and chemistry text books there is a lot of talk about energy transitions in atoms due to photon absorption/release. However atoms can also absorb and release energy ...
0
votes
0answers
26 views

What are first and second order phase changes?

In my thermodynamics lecture course, the Ehrenfest equation for a second order phase transition was derived from considering the following graphs, however there was little context in the section for ...
0
votes
1answer
27 views

Query about change in $\Delta G$ during a chemical reaction and finding equilibrium

TLDR : Can someone explain the graph at 27:40 in the following lecture: Full section length is from 21:12 to 27:40 https://www.youtube.com/watch?v=Cc2l1QTTZA4&list=PLA62087102CC93765&index=...
1
vote
0answers
34 views

Fires with chlorine

could a fire with it's fuel consisting of mostly carbon like coal or wood use chlorine instead of oxygen. My thinking goes that when fire burns it sucks in oxygen and that bonds with carbon to make ...
0
votes
0answers
63 views

What was the pressure generated in Fat Man to compress the fissile material?

Fat Man was an implosion-type nuclear weapon. What was the pressure generated by the chemical explosive?
0
votes
0answers
24 views

Why is $\Delta_r G^0$ temperature dependent in the van 't Hoff equation?

One can derive for a equilibrium reaction between ideal gases $$\sum_i \nu_i R_i \leftrightarrow \sum_i \nu_i P_i $$ the expression $$ \Delta_r G^0=-RTln(K) \quad \textrm{where} \quad K=\frac{\Pi_{\...
0
votes
2answers
27 views

Do different ways of vaporizing water have different efficiencies?

Question Are some ways of vaporizing 1kg of pure water at ATP more efficient? Specifically cold vs hot methods of vaporizing water. Background There are many ways of vaporizing water. Some ways ...
0
votes
0answers
34 views

High boiling-point oil

What is the highest boiling point oil in the world? I mean oil with a boiling temperature above 300 ° C. How can I find its physical property?
0
votes
0answers
16 views

Atoms with energy differences corresponding to wavelengths 19.05 cm, 24.45 cm and 25.48 cm

I was just wondering whether there are any known atomic transitions in Oxygen, Nitrogen, Hydrogen or Helium atoms/ions which emits wavelengths in any of the regions: 19.05 cm, 24.45 cm and 25.48 cm. ...
3
votes
5answers
577 views

How can the mechanism of electrons in an atom be explained? [closed]

I am a high school student who takes both Physics and Chemistry. Recently I learnt about the quantum mechanical point of view of looking at electrons or nuclei. I also learnt that the wave functions ...
0
votes
1answer
30 views

How can a chemical substance explode, producing only solid products?

Silver acetilyde, like some other salts of silver, is unstable and explodes with great force. However, unlike almost all other explosive compounds, it doesn't produce any gases - it only produces ...
49
votes
6answers
6k views

Because things smell, is everything evaporating?

Everything, in theory, can have a smell, but that is not the whole point of this question. My main query is, since things do smell, does that mean that everything is slowly evaporating (or, ...
0
votes
5answers
134 views

Does oxygen and carbon dioxide separate in a closed box?

If I have "air" in a closed box, does oxygen and carbon dioxide get separated over time? Does oxygen fill upper part of box and carbon dioxide lower part of box? How about if upper part of box is ...
4
votes
2answers
111 views

Why is 99% isopropyl alcohol preferred for a DIY cloud chamber?

Simple cloud chamber construction is described in various places and all seem to use 90% - 99% isopropyl alcohol as a start. What property does this have that makes it an essential component for ...
0
votes
0answers
8 views

Salt Concentration relationship with specific heat capacity. Theories for linear relationship

I was curious about the relationship between salt concentration of a solution and its specific heat capacity. I've seen research (and made my own graph too) where the data shows there's a negative ...
0
votes
0answers
18 views

Is it possible to convert carbon soot/ black carbon in mg to CO2-equivalent? If so, how?

Since global warming is expressed in terms of carbon emissions or CO2 equivalent, can the short lived carbon soot/ black carbon that is produced from incomplete combustion be expressed in terms of CO2 ...
1
vote
1answer
33 views

How does boiling-point elevation due to a solute affect the steam/gas that is created when boiling?

Consider the following situation: We have a pot of strong brine (for concreteness let's say 25g of NaCl per 100ml of water, at standard conditions) and heat it to a boil. How will the salt content ...
0
votes
1answer
32 views

The dependence of entropy on temperature?

I am wondering why the entropy will increase faster for a gas (when compared to a liquid/solid) when temperature increases? Is it because the heat capacity for a gas is lower than solids and liquids? ...
0
votes
1answer
41 views

What is a “Doppler instability”?

In the paper "Flow-induced control of chemical turbulence" by Berenstein and Beta, the term "Doppler instability" is mentioned in the context of the Belousov-Zhabotinsky reaction. I am looking for a ...
1
vote
0answers
42 views

Lagrangian for a concentration field

If I have a field, $\phi(x)$, representing the concentration of particles in a one dimensional space, what is the Lagrangian for this field? My initial guess was $$\mathcal{L} = \int dx[\frac{1}{2}\...
1
vote
0answers
79 views

Why does lithium have a total electronic spin of 1/2?

The book I'm reading analyses atoms by only looking at the last eletrons, and saying that their wave function must be anti-symmetric. I understand the case of Helium, the spin function must be anti ...
2
votes
1answer
95 views

Knudsen Number and pressure

When computing the Knudsen number to know if the continuum hypothesis can be applied as $\frac{k_B T}{p \sqrt{2} \pi d^2 L}$, do we use the static or total pressure of the free stream? My object is ...
6
votes
1answer
85 views

Why does the rate of a chemical reaction depend on partition functions according to the ratio $Q^\ddagger/Q$?

I'm trying to understand isotope effects on the rates of chemical reactions, which, surprisingly, can be very large in some cases. In treatments of this problem, I see a lot of expressions that ...
8
votes
3answers
153 views

Why does the mean speed of gas particles include $\pi$?

In chemistry we are learning about kinetic molecular theory (KMT) of gasses, and I just couldn't help being surprised when I saw $\pi$ in the equation of mean speed. I know that whenever $\pi$ is ...
1
vote
2answers
41 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 ...
0
votes
1answer
40 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 : ...
0
votes
0answers
17 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 ...
0
votes
1answer
37 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 ...
0
votes
0answers
15 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 ...
0
votes
1answer
35 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 ...
2
votes
1answer
50 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 ...
1
vote
2answers
63 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. ...
1
vote
0answers
22 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{...
7
votes
1answer
155 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 ...
0
votes
0answers
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 ...
0
votes
0answers
11 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 ...
2
votes
0answers
29 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 ...
0
votes
1answer
35 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 ...
1
vote
2answers
67 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 ...
0
votes
0answers
16 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 ...
0
votes
0answers
10 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.