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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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Where does the Pauli Repulsive Force come from that counteracts the attraction between atoms and ions? [duplicate]

I'm learning about such things as ionic and covalent bonds, and the reason given for the ionic bonds is electrostatic attraction. However, if that were true, then the two ions would accelerate toward ...
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Why does burning magnesium explode when sprinkled with water?

Magnesium powder burns extremely well and reaches temperatures of 2500°C. However, attempts to extinguish such a magnesium fire with conventional water (e.g. from a garden hose) only make it worse: ...
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What does activation energy actually do?

Spontaneous (exothermic) chemical reactions often require a push from the addition of externally supplied energy. This energy is often called activation energy. What does activation energy actually do?...
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FCC-to-BCC phase transition in NaCl, Buckingham or Lennard-Jones potentials?

Background The transformation from B1 (face centered cubic (FCC) type) to B2 (body centered cubic (body centered cubic (BCC) type) structures is one of the best documented high pressure phase ...
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What's the underlying particle physics of endothermic reactions?

I don't just mean reactions that require heat to proceed, storing surplus energy in chemical bonds. I wonder about strongly endothermic reactions that suck heat out of environment. You take some ...
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Physical Chemistry: What's the relationship between orbital overlap and barrier shape?

This is a question for the physical chemists out there. For a given chemical reaction there is a barrier to traverse in order to proceed from reactants to products. Reactants e.g. an organic base ...
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565 views

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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215 views

Earnshaw Theorem for ionic solids

Is a single molecule of sodium chloride (say) or a cluster of molecules of NaCl unstable, although macroscopically NaCl is in fact, stable? How can I reason this based on Earnshaw's theorem?
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The AntiBonding Orbital with Shrinking Interatomic Distance

I guess this is more of a chemistry question, but whatever. I think it's interesting. Suppose you had two bare atomic nuclei. For concreteness, lets assume the nuclei are the same with atomic ...
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242 views

Electron spin and chemical properties

I just learned about spin in class and I recall my professor vaguely mentioning how the spin of an electron is what determines certain chemical properties. I have trouble seeing why. Suppose an ...
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8answers
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Is there any reproducible tested evidence for Ni-H cold fusion? [closed]

The main replications of cold fusion, the ones that are beyond reproach, used Pd/d as the system. But commercial developers have often claim to use Ni-H to achieve similar effects. The claims include ...
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Is there no radioactive decay between nuclear fusion and solid material formation?

I'm aware my question might be considered a duplicate of this one: Radio-dating and the age of the earth I read that one and I looked everywhere and I still can't find my piece of mind. I would ...
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Sodium sometimes absorbs orange-yellow light, sometimes emits it? Huh?

Usually, we are told that sodium emits orangish-yellowish light, which is why city streetlamps are that color. Now, I read in New Scientist magazine that exoplanet WASP-96b is bluish because the ...
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Why Does Air Hold More Water When the Air is Warmer?

I know that when the temperature of the air rises, the maximum amount of Water it can hold before the water condenses to water droplets increases. But why is this - has it got something to do with ...
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954 views

Why does pure gold melt at 300 degree Celsius?

The actual melting temperature of gold is 1000° C. However, I noticed when pure gold wire whose diameter is 3 mills is put into the molten blob of solder (60% tin + 40% lead), which is at only 300° C,...
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Why does a pitcher with lemon juice have foam, while one with pure water does not?

Whenever I pour water into lemon juice (pouring directly from the tap into the pitcher, not quietly along its edge) I get a foam on top: The same pitcher with water (same water tap, pitcher, time ...
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Can a liquid shrink as something is dissolved into it?

Not much more to add. By shrink, I mean become more dense at the same pressure and temperature. And I don't mean vol(A+B) < vol(A) + vol(B). I'm sure this is possible. Is it possible to ...
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553 views

Why soap bubbles are made of soap?

Why are soap bubbles made of soap? What I know is to have stability in bubble, waterproofing agents should me mixed, but soaps are water wetting agents, and water wetting agents will decrease angle ...
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Questions about the strange character of antimatter

Its been a few days and i have just been introduced to the concept of antimatter. Every Speck of matter in the world has its anti form basically that we have antimatter whenever we have matter. But I ...
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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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Understanding the Bennett Acceptance Ratio (BAR) method

The Bennett acceptance ratio method (BAR) is a method for computing free energy differences. See also Wikipedia Alchemistry.org Original publication I have problems understand the very beginning of ...
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How Do Bubbles in Sodas Know to Form?

Carbonated water is $H_2 0$ with $H_2 CO_3$ in it. $H_2 CO_3$, carbonic acid, decomposes into water and $CO_2$, carbon dioxide. When the cap is closed on a bottle of carbonated water, there is a ...
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Does the Dirac equation ever get used in Physical Chemistry?

I'm just curious as to know if there are any examples in physical chemistry or condensed matter physics where the Dirac equation is preferable to the Shrodinger equation for making predictions on the ...
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The 2011 Nobel Prize in Chemistry

As far as I understand a new pattern of crystal growth has been found experimentally. How does it relate to the known 2D and 3D nucleation and growth of crystals? The dominating theory of crystal ...
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How to compute this change of Gibbs energy for a Van der Waals gas?

The change of Gibbs energy at constant temperature and species numbers, $\Delta G$, is given by an integral $\int_{p_1}^{p_2}V\,{\mathrm d}p$. For the ideal gas law $$p\,V=n\,RT,$$ this comes down to ...
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Physics of a burning log of firewood

According to my knowledge, heat is nothing but the result of the vibrations of atoms and molecules. I guess this mean that in heating up a gas or liquid, we are increasing the rate at which the ...
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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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Dissolving oxygen into water

I was wondering how one would actually calculate how much oxygen would dissolve into water given the necessary initial conditions, and what those initial conditions would need to be. I assume they ...
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1answer
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Addition of a neutral electrolyte to water— how can it increase conductivity?

Sparked off by Is sea water more conductive than pure water because "electrical current is transported by the ions in solution"? This question really belongs on chemistry.SE, which is still ...
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Why is oxygen in a triplet state and what are the consequences?

From Wikipedia here and here: ''Almost all molecules encountered in daily life exist in a singlet state, but molecular oxygen is an exception.'' ''The unusual electron configuration prevents ...
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When putting water on two pieces of paper they bond. Is that due to van der Waals bonds?

I've been wondering what keeps two pieces of wet paper together when in contact. Does water have any adhesive property? Or does it decompose something from the paper and creates some kind of glue? I ...
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What is the mechanism of dielectric saturation?

It is known from experiments that the dielectric constant of a solvent might decrease in regions where there is a strong electric field, for example, near a highly charged ion in an infinitely dilute ...
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Why does the thermal conductivity of water decrease with increasing salinity?

Intuitively I would expect the thermal and electric conductivity to be positively related, and since electric conductivity increases with salinity, so should thermal. But according to this table (p.10)...
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Force field for calcium ions, potassium ions and water in molecular dynamics

I want to adapt my existing MD simulation so that it can handle these three species. For the interactions of the ions I thought that I would use the coulomb potential, but I don't know what sort of ...
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634 views

Voltage drop over a cell membrane

Again, a problem from exam preparation: [A] cell's membrane allows sodium ions to pass through it, but not chlorine ions. The cell is placed in a salty solution with a ten times higher ...
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936 views

Energy levels in disordered organic semiconductors?

Now in disordered organics, the band picture is thrown out the window, from what I can tell (due to lack of symmetry). But don't HOMO/LUMO levels basically take the place of conduction/valence bands ...
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Chemistry of water under pressure [closed]

What is the structure of water under extreme pressure, like the bottom of the ocean on a moon like Europa.
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Why are the lighter halogens gases?

In the periodic table of the elements, only a few of the elements are gases at standard temperature and pressure. Those elements include the noble gases some of the halogens, and a few of the elements ...
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Is Uranium renewable, or will this science fiction scenario become reality?

In my imagination, nuclear power could disapear when we use up all the uranium generating electricity, or exploding nuclear bombs. Is uranium a renewable resourse? if not, can we prove that this ...
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Does salt affect the boiling time of water?

If I have 1 cup of water on the stove and another cup of water with a teaspoon of salt. would the salt change the boiling time of the water?
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role of entropy in gibbs free energy intuition

I have looked at various derivations of the Gibbs free energy equation and the underlying definition of the Gibbs free energy. However, I have been unable to attain direct insight/intuition over the ...
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Jet turbine blades from single crystals, how are they formed?

I know about nothing about crystals, although I do know a bit more about jet turbine engines, and I definitely know that you don't want the fan blade hitting the fan housing. The reason given in the ...
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What would make the bottom of my cocktail glass develop a fractured pattern like this?

I left out the remnants of my Long Island Iced Tea. This was a mixture of various liquors, lemon juice, Splenda, and water from the melted ice. It was left on my kitchen counter for several days: ...
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What compounds or elements only have one phase or two phases?

Wood appears to be one. I think gases like helium and hydrogen cannot exist in the solid state under normal pressures, correct? And why do those "phase cheaters"-- those elements/compounds which ...
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451 views

Why does smashing a TV remote load its batteries?

Many times I had the same problem: my TV remote's batteries were too weak for it to operate, but then, when I shook the remote a bit and smashed it on my palm, somehow the remote regained its ability. ...
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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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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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Notation for electronic states of molecules

I came across a question using a notation for electronic states of molecules that I do not understand. The question talks about electrons in molecules of $^{27}$AlH getting excited to $A^1\Pi $ ...
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Spacetime curvature effect on chemistry

Do current chemistry / astrophysics / stellar chemistry calculations include the effects of the curvature of spacetime on chemical reactions? For example, the heat transfer from a point closer to the ...
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Why does NaCl (aq) conduct electricity but NaCl (s) does not?

Why does sodium choloride in its solid state not conduct electricity, but in its aqueous solution state it conducts electricity easily?