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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3answers
5k views
Why does the water rise?
It's a very popular experiment (eg), from elementary school : put a burning candle on a dish filled with water, cover the candle with an inverted glass: after a little while, the candle flame goes ...
17
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4answers
1k views
Could the Periodic Table have been done using group theory?
These three questions are phrased as alternative-history questions, but my real intent is to understand better how well different modeling approaches fit the phenomena they are used to describe; see 1 ...
15
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3answers
508 views
Why the distribution of elements on Earth?
I've been wondering exactly why the elements are distributed the way they are on Earth. The heavier elements have their origins in the centers of stars, or in supernovae. After the death of the stars, ...
14
votes
4answers
2k views
Boiling water and salt
I would like to have a good understanding of what is happening when you add salt to boiling water.
My understanding is that the boiling point will be higher, thus lengthening the process (obtaining ...
12
votes
6answers
1k views
Where should a physicist go to learn chemistry?
I took an introductory chemistry course long ago, but the rules seemed arbitrary, and I've forgotten most of what I learned. Now that I have an undergraduate education in physics, I should be able to ...
11
votes
2answers
2k views
Why do grapes in a microwave produce plasma?
Some of you may know this experience (Grape + Microwave = Plasma video link):
take a grape that you almost split in two parts, letting just a tiny piece of skin making a link between each half-part.
...
8
votes
5answers
3k views
How was Avogadro's number first determined?
I read on Wikipedia how the numerical value of Avogadro's number can be found by doing an experiment, provided you have the numerical value of Faraday's constant, but it seems to me that Faraday's ...
8
votes
3answers
529 views
What is the angular momentum spectrum of an sp${}^3$ electron?
So, one thing has been annoying me ever since I learned about orbital hybridization: you explain the shape of molecules by postulating that the orbitals of multi-electron atoms are linear combinations ...
7
votes
3answers
2k views
What makes the difference between ionic and covalent bonds?
Backstory: When I learned about chemical reactions, there were two types of molecular bonds: Ionic, where an atom or compound molecule with a low valence number loses those valence electron(s) to one ...
7
votes
3answers
870 views
Is the Mendeleev table explained in quantum mechanics?
Does anybody know if there exists a mathematical explanation of Mendeleev table in quantum mechanics? In some textbooks (for example in F.A.Berezin, M.A.Shubin. The Schrödinger Equation) the authors ...
7
votes
2answers
438 views
Is mass-energy conversion in chemical reactions experimentally observable
This is a common point of argument on internet forums. I think it is fairly well established theoretically that there is a very small amount of mass converted to energy in an exothermic chemical ...
6
votes
2answers
942 views
How are the calories in food calculated?
This is intended to be a fun question. Calorimetry used for calculating the heat generated from chemical changes has been around for centuries, however, I suspect the process for calculating food ...
6
votes
2answers
1k views
Why is quicksilver (mercury) liquid at room temperature?
This is a nice question when you find it out, and I am really looking for a proper answer.
Take quicksilver (Hg) in the periodic table. It has one proton more than Gold (melting point 1337.33 K), and ...
6
votes
2answers
292 views
Explaining valence with quantum mechanics
Can anyone give me a quantum mechanical explanation of the theory of valence? (i.e. why atoms bond just enough to have a complete orbital)
EDIT: To clarify, I already have an idea of why atoms bond, ...
6
votes
2answers
2k views
Why does a salt solution conduct electrical current?
How does e.g. sodium chloride (aq) conduct electricity? By accepting electrons (unlikely since they already have a full outer shell)? But they can't be hopping around themselves, can they? I mean, if ...
6
votes
2answers
277 views
Statistical Mechanics treatment of the reaction process?
I'm searching for an at least semi-rigorous Statistical Mechanics description/treatment of a (spatially resolved) chemical reaction process of a macroscopic portion of at least two different species ...
6
votes
1answer
107 views
How much Bicarbonate of Soda and Vinegar would I need to reach space?
So here is my problem - as part of my job I present some science demonstrations to children and one of the tricks I regularly use is the bicarb/acetic acid rocket. I thought the other day that a ...
5
votes
2answers
110 views
Solidification by the application of heat
When you add heat to a liquid (or a fluid), can it be solidified? If not, why in the world does an egg's stuffs become solid (or at least no more a liquid) when you 'boil' it in water?
5
votes
3answers
522 views
Why is Avogadro's hypothesis true?
Why is the number of molecules in a standard volume of gas at a standard temperature and pressure a constant, regardless of the molecule's composition or weight?
Let's say I have a closed box full of ...
5
votes
2answers
2k views
Why are the noble metals inert?
I am wondering: The noble 'gases' are inert because they have closed shells and don't want to give that up. But the noble metals, such as Copper, Silver, Rhodium, Gold, don't seem to have this.
For ...
5
votes
1answer
424 views
What happens to chemical compunds that include radioactive nuclei, when those decay?
Say you have a chemical compound made up of one or more radioactive nuclei. If the nucleus decays, does the compound?
Possible outcomes I can think of:
the compounds continues to exist if a ...
5
votes
2answers
227 views
In condensed matter simulations, how is particle number density computed in practice?
I have been reading a recent paper. In it, the authors performed molecular dynamics (MD) simulations of parallel-plate supercapacitors, in which liquid resides between the parallel-plate electrodes. ...
5
votes
1answer
169 views
What equation describes the electrostatic potential in these circumstances?
I have a solver for Poisson's equation and it works nicely. It uses finite differences. It works in the presence of multiple dielectrics.
It also solves the Poisson Boltzmann equation. That is, fixed ...
5
votes
2answers
211 views
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 ...
4
votes
3answers
911 views
Why is the canonical ($NVT$) ensemble often used for (classical) molecular dynamics (MD) simulations?
Molecular dynamics (MD) simulation is a common approach to the (classical) many-body problem. It relies on integration of Newton's equations of motion to simulate the trajectories of many (e.g., ...
4
votes
3answers
145 views
Do electrons in multi-electron atoms really have definite angular momenta?
Since the mutual repulsion term between electrons orbiting the same nucleus does not commute with either electron's angular momentum operator (but only with their sum), I'd assume that the electrons ...
4
votes
3answers
350 views
Nanorobots. What stops us from producing them yet?
If we can already predicts accuratelly motion on molecular levels, what stops us from developing small robots to, for instance, navigate through our blood vessels looking for cancerous cells and ...
4
votes
1answer
259 views
What is the purpose of a “protect from light” warning?
Some food or medical items, like rasberry juice concentrate I just bought, have a "protect from light" warning on the label. How can light influence products like milk and what does this warning mean ...
4
votes
1answer
1k views
How to know what materials are good conductors of electricity?
I'm not asking a question like "Is the wood conductive?". No. I'm asking what properties do they have to have to be good conductors. Theoretically I mean. Thanks.
4
votes
1answer
193 views
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 ...
4
votes
1answer
414 views
Energy per particle vs. chemical potential vs. evaporation energy
There is a system of N particles. They interact and are bound together with a binding energy Eb (or potential energy). To characterize the system there are multiple terms
Energy per particle Eb(N)/N
...
4
votes
1answer
175 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 ...
4
votes
0answers
87 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 ...
4
votes
2answers
202 views
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 ...
3
votes
3answers
2k views
Why is the energy density of gasoline so high?
We sometimes play a game in my family whereby we trace the energy for a device back to it's source:
The Xbox got power from the wall.
The wall got power from the local transformer.
The transformer ...
3
votes
3answers
373 views
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 ...
3
votes
5answers
2k views
Conversion of mass to energy in chemical/nuclear reactions
Is mass converted into energy in exothermic chemical / nuclear reactions?
My (A Level) knowledge of chemistry suggests that this isn't the case. In a simple burning reaction, e.g. $C+O_2\to ...
3
votes
2answers
112 views
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:
...
3
votes
1answer
271 views
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 ...
3
votes
1answer
743 views
Chemical potential interpretation
Something that has bothered me for a while regards the interpretation of chemical potential for different statistics. While I understand its meaning in metals (and its relation with the Fermi ...
3
votes
2answers
703 views
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. ...
3
votes
1answer
195 views
determination of voltaic cell voltage
if i understood this correctly, the determination of voltage for a specific voltaic (gallvanic) cell is determined only by the chemical correlation between the two metals. is this true?
for an ...
3
votes
2answers
1k views
Widom-Larsen Theory
Does the Widom-Larsen theory pose a credible underpinning for Low Energy Nuclear Reactions, often incorrectly referred to as "Cold Fusion"?
http://arxiv.org/abs/cond-mat/0505026
3
votes
2answers
183 views
When do thermal and chemical equilibrium not coincide?
What is an example for a system, which is in chemical equilibrium, but not in thermodynamical equilibrium?
And what about the other way around?
It seems to me, that as long as Parameters like ...
3
votes
1answer
375 views
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 ...
3
votes
1answer
355 views
Why is E85 less efficient than straight gasoline?
Why is straight gasoline (or whetever the mixture was before the introduction of ethanol) more efficient (ie, more miles/gallon) than E85? I've known since it's introduction that E85 was less ...
3
votes
1answer
202 views
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 ...
3
votes
1answer
152 views
Why do hydrogen atoms attract?
That is, why is the potential energy with the orbitals overlapping less than with the Hydrogen atoms 'independent'.
Similarly, why is a noble gas configuration stabler than if an electron were to be ...
3
votes
2answers
180 views
What physical forces give rise to the peculiar bond angle of hydrogen peroxide?
In one of the Periodic Table videos, Prof. Poliakoff shows a model of a hydrogen peroxide molecule and claims that the H-O bonds will always be at right angles to each other. I have a rudimentary ...
3
votes
1answer
415 views
How does a stronger magnet affect the MRI image quality?
In which ways is a stronger magnet better for magnetic resonance imaging? I read that:
The field strength of the magnet will influence the quality of the MR image regarding chemical shift ...
