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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150 views

Why does the Gibbs free energy not decrease ad infinitum?

I would like to ask which guarantees if the Gibbs free energy has a minimum in closed system (e.g. in a chemical reaction system) at constant pressure and temperature? Why does it not decrease ad ...
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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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234 views

What are enthalpic and entropic forces?

Am I right when thinking of entropic force to be an entropy minimizing mechanism and enthalpic force to be an energy minimizing mechanism (which is basically an entropy maximization mechanism). What'...
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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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Calculating molal depression constant from latent heat of fusion

Calculate molal depression constant of water if latent heat of fusion of ice at $0^\circ \text C$ is $80 \text{ cal/g}$. All I could find was the equation $K_f=\frac{0.002T^2}{L_f(\text{in cal/g})}$ ...
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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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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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57 views

Why are there less bubbles the second time I pour soda in the cup?

I poured some Pepsi into a mug, and it foamed, and I poured until the foam was at the top of the glass. I waited a few seconds for the bubbles to go, and the liquid level was revealed to be at around ...
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153 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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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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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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1answer
181 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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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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64 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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1answer
173 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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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
81 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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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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Meaning of the term “phase” in chemistry and thermodynamics

I have some doubts about the definition of the term “phase” in chemistry and thermodynamics (is the meaning the same?). The "textbook" definition is: "A phase is a form of matter that is uniform ...
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1answer
57 views

When to include chemical potential in Gibbs equations?

I'm struggling to understand when to and when not to include the chemical potential in the differential forms of the thermodynamic potentials. In principle I would assume that any system wherein the ...
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1answer
45 views

Another Free Energy Question :P :)

Hello StackExchange users. Before you read my question I would like to thank you for taking the time to help me out :). So anyways, my question is about the formation of coal seeming to break the laws ...
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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
65 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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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?
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41 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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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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36 views

Conditions to dissolve $CO_2$ in water?

I hope this question is appropriate for the Physics SE, although it involves a practical situation rather than inquiring purely about theory. I've been trying to create carbonated water at home using ...
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1answer
57 views

Water from air concept – is this plausible?

Here’s an idea I had: Consider how a rocket stove works.. There is an inlet where wood is fed into the stove and an outlet for which the exhaust can vent. Very simple but very effective. Now apply ...
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2answers
36 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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How to deduce the SK (Slater-Koster model) integral for two-center with px, py orbital?

I would like to get the Slater-Koster integrals from formula: $$ \sum{R_j}expi\textbf{k}\cdot(R_j-R_i)\int\psi^*_n(\textbf{r}-\textbf{R}_i)H\psi_m({r}-\textbf{R}_j)d\nu, $$ (1) where the sum is ...
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1answer
27 views

Sintering of Yttrium barium copper oxide

I will do an experiment on superconductors, specifically $\text{YBa}_2\text{Cu}_3\text{O}_7$, and I am curios about some steps in the preparation. The starting materials are $\text{Y}_2\text{O}_3$, $\...
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1answer
231 views

Ionization Through Atomic Collisions - Any Reason(s) for Its being Unimportant?

The dominant processes which contribute to the ionisation of a gas (which is possibly hot and dense) are often deemed to be electron-impact ionization ($A + e^- \rightarrow A^+ + e^- + e^-$) and photo-...
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Why does ice cream get harder when colder?

What would seem to be a silly question actually does have some depth to it. I was trying to scoop out some of my favorite soft name-brand ice cream when I noticed it was frozen solid, rather than its ...
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33 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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2answers
52 views

How are atoms supported on each other in a material?

Suppose we have a ball made up of iron. There are a "lot" of atoms in the ball. My question is "how" are the atoms supported on top of each other? And, is it due to the repulsion of electrons the ...
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1answer
55 views

Will the mass of a stick of dynamite be conserved when it is exploded?

If a stick of dynamite is blown up in a hermetically sealed chamber, the mass of the chamber and fragments, the heat, sound, and light would still be equal to the original mass of the chamber and ...
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2answers
55 views

Minimal work required to produce ice at room temperature

I'm wondering about the most efficient way of producing ice from water at room temperature. First of all: why, in principle, do we need to put in work to do so, if water gives off energy while ...
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1answer
25 views

Which reference should I use for molar masses of chemical elements?

This question is more related to the academical application of Physics than to Physics per se. I'm currently doing my thesis, and it involves a lot of molar masses in the calculations. I would like to ...
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Convert Normal water to cool instantly [closed]

Is it possible to convert the hot/normal water to cold steam instantly(may be within 1/2hr) without using refrigerators etc. If yes, how far can the cold steam travel. I am not sure with all the fluid ...
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2answers
234 views

Are there any types of lasers that emit orange and yellow light?

That is, without the introduction of nonlinear optics for frequency multiplication. In the case of orange light, I've often wondered in orange minerals like Lead Molybdate (PbMoO4) fluoresce the way ...
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236 views

Copper density modification

Can you increase the density of a material surface (metal) by surface treatment? For example commercial copper. If we take the ordinary OF copper (99.95%), I would expect not to have the tabulated 8....
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1answer
35 views

Why are processes where $\Delta G \le 0$ considered spontaneous?

I understand how, for any process where starting pressure and temperature start and end points are the same, that $$\Delta G \le 0$$ But I don't see how, from looking at this, that when $\Delta G$ ...
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1answer
48 views

Predicting pressure of propane gas in container based on temperature

I'm a mathematician and computer scientist, and for this particular problem I would benefit from some physics/chemistry expertise. I've already asked this question on chemistry stack exchange, but I ...
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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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2answers
373 views

Why is argon a noble gas but not, say, beryllium or palladium?

Why is argon a noble gas given that the 3d subshell is still empty? More generally, why is it that the filling of a p sub-shell makes an element noble rather than s, d, or f sub-shells, or completed n-...
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Why doesn't increasing the temperature of something like wood or paper set them on fire?

Imagine we have paper book. If we put this into a pan and increase its temperature, this book would not catch on fire. If on the other hand the book interacts with this heat source directly, it does ...
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Why is grass green? [closed]

How come grass isn't blue or pink, but apparently, it is according to this scientist it is every color but green. I also got told by my teacher that grass is only green and no other color. So I am ...
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239 views

Theoretical physics for better batteries?

It is Earth day, so I started thinking about the theoretical physics problems that could help reduce greenhouse-gas emissions and fight climate change. We actually have a reasonable range of ways to ...
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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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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, ...