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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8 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 implosive?
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2answers
964 views

Calculating internal energy of formation

I'm working on some code to simulate combustion at constant volume instead of constant pressure and I need to calculate the internal energy of formation for the species involved because I can only ...
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1answer
238 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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Can we estimate what partial pressure 10 mM $H_2$ corresponds to at a depth of 1 km depth (=100 bar of water)? [closed]

I'm stuck here. I could use the equation of state and just assume the volume of water doesn't change with temperature and pressure but that's not true. Also, wouldn't I have to use Henry's law at some ...
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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_{\...
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Can someone explain how this occurs? [closed]

Initial spillage of a liquefied gas from a pressure vessel behaves differently to that described above. In this case the liquid, on escape, is at a temperature close to ambient. However, the high ...
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2answers
26 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 ...
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31 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?
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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. ...
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1answer
180 views

How to calculate the mass of gas needed to fill a cylinder to a certain pressure?

I m tasked with a tricky situation. I need to calculate the exact amount a tank can take in gas. But I dont know the volume of the tank. I just need to make sure that the tank reaches the right ...
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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, ...
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2answers
90 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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575 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 ...
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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 ...
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4answers
109 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 ...
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1answer
820 views

What is the densest material on earth? [closed]

Apart from the elements, do we know of materials that are denser (and not including exotic and theoretical matter)? I.e. can an alloy be denser than the sum of its compounds, for example if the new ...
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1answer
377 views

What's the densest known material that has been made in macroscopic quantities?

I'm aware that the densest stable element is osmium at 22.61 g/cm3. And that there are unstable elements such as hassium and meitnerium which are predicted to have densities of 41 g/cm³ and ...
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98 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 ...
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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 ...
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Can we fully simulate molecular physics?

Is our knowledge of physics complete enough to achieve fully natural simulations of molecular interactions in a computer simulation? How far off are we? Reason for question: I wonder how far we are ...
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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 ...
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17 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 ...
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1answer
168 views

How can we use conductivity measurements of water to find hydrogen ion concentration of water?

How can we use conductivity measurements of water to find the hydrogen ion ($\mathrm{H}^+$) concentration in water?
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1answer
30 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? ...
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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 ...
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1answer
39 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 ...
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1answer
77 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 ...
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1answer
53 views

Why does the Anode and not the Cathode corode during eletrolysis of water into $H_2$ and $O_2$?

After experimenting with the production of Hydrogen from salt water, I kept on noticing that the Anode (-) gets coroded and not the Cathode (+). Is it perhaps that water in itself is a naturaly ...
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2answers
206 views

How much energy is needed to make fire?

I'm so curious about fire. So I searched a lot in the internet. And now, I knew that fire is some kind of chain reaction and combustion energy make the other molecule hot and the other molecule makes ...
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1k views

The exact mechanism of energy release durning bond formation on the atomic level

Image a situation: We have two atomic hydrogen atoms. We magically collide them together dead center and perpendicular. Each atom has exact amount of kinetic energy. We collide them with precisely ...
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39 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}\...
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77 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 ...
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1answer
95 views

Red colour of the Great Red Spot

In Wikipedia it is mentioned: "It is not known exactly what causes the Great Red Spot's reddish color. Hypotheses supported by laboratory experiments suppose that the color may be caused by ...
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What meaning do changes in the absolute value of Gibbs free energy have in a simple expansion process?

Below is a simple representation of the thermodynamics of a steam turbine. Stream kinetic and potential energy changes are neglected and no other type of non-PV work is done besides shaft work. ...
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3answers
152 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 ...
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1answer
225 views

Can a plasma ball light up minerals that fluoresce?

I want to know if I could use a plasma ball to light up a UV poster that are typically activated by blacklights. option 1: using light from the globe According to my research it seems that the light ...
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1answer
191 views

What's the minimum time scale for a candle to be lit in order for it to establish a steady state?

My Understanding When a candle is lit initially, it goes through a few stages (see, e.g. this explanation from the National Candle Association): Wick burns. Crusted wax on wick melts, evaporates ...
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1answer
184 views

Microscopic explanation of colligative properties from the entropy related viewpoint

In the chapter 28.6 of book "Concepts in thermal physics "(2nd edition) written by Stephen J. Blundell, there is a sentence says "Adding a small quantity of solute to a solvent increases the entropy ...
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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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1answer
38 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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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
36 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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1k views

Handling halogen lamps

When consulting manuals, electricians, online sources, etc., they always instruct you to handle halogen light bulbs with gloves. The "explanation" that usually accompanies this statement is that oils ...
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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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1answer
29 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
48 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
57 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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1answer
2k views

How many calories in a block of wood?

I was recently thinking about the human body and the energy we get from food. I understand we don't have the ability to properly digest certain things like stones and wood and grass, but if we did, I ...
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16 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
152 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 ...