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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16
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5answers
23k 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. $$\mathrm{C + O_2 \...
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6answers
9k 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 ...
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6answers
16k views

What enables protons to give new properties to an atom every time one is added?

How does adding one more particle to the nucleus of an atom give that atom new properties? I can see how it changes it's mass, that's obvious... But how does it give that new atom different properties ...
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4answers
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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 ...
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2answers
4k views

What happens to chemical compounds that include radioactive nuclei, when those decay?

Say you have a chemical compound made up of one or more radioactive nuclei. If these nucleus decay, does the compound decay as well? Possible outcomes I can think of: the compounds continues to exist ...
14
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4answers
17k views

Why do covalent bonds form?

why in a covalent bond are "the bonded electrons are in a lower energy state than if the individual atoms held them at the same proximity"? Also is it correct that " I think when you start pushing ...
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2answers
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 ...
18
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4answers
93k views

Why does ice have a lower density than water?

Can someone explain me why is ice less dense than water? As I know, all solids are usually denser than the liquids (correct me if I am wrong).
1
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1answer
129 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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4answers
47k views

Is it possible to flow current in open circuit?

As I know a battery is an example of a closed circuit where it can then produce electricity , electrons will flow from negative pole to positive. A chemistry representation of this battery is for ...
21
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3answers
10k views

What is the quantum mechanical explanation of the octet rule?

What is the quantum mechanical explanation of the octet rule? In other words, what makes the octet rule be true from a quantum mechanical view? How we explain what makes some atoms don't follow the ...
7
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2answers
680 views

How does covalent bonding actually work?

How does covalent bonding actually work? Consider the molecule $O_2$, which has a double covalent bond between the oxygen molecules. Chemistry texts say that a double covalent bond occurs because this ...
12
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1answer
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How do candles and wicks work?

The wick of my tea candle was buried in wax. So I lit a piece of paper and stuck it in the wax. Now the wax is burning off the paper, as if that were the wick. The wax itself wouldn't light on fire ...
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2answers
764 views

Does stirring a liquid add heat $Q$ to a system? [closed]

I was given a question, "A thermos bottle containing milk is shaken vigorously. Consider the milk as the system. (a) Will the temperature rise as a result of the shaking? (b) has heat been added ...
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2answers
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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?
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1answer
98 views

Basic energy question

How do we know something contain energy or not? P.S.: I don't really understand how energy should be interpreted. Until today I always thought that energy is some kind of magic that makes stuff ...
120
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6answers
21k views

Why does the humidifier make a stove's flame orange?

Just like this guy's, the color of my stove's flames were affected by the humidifier as well. Why does this happen? Is it a good thing or a bad thing ?
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3answers
2k views

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 ...
30
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4answers
11k views

Why does temperature remain constant when water is boiling?

As I understand it, during boiling the input of heat destroys or re-arranges the hydrogen bonds. It is used, in other words, against the potential energy of the intermolecular bonds. But if some ...
12
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2answers
142k views

How can a salt solution conduct electrical current?

How does a sodium chloride solution conduct electricity? I know that sodium chloride dissociates into sodium and chloride ions in water, so when a voltage is applied, those ions can move. However, if ...
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3answers
3k views

Extra vibrational mode in linear molecule

When calculating the number of vibrational modes for a molecule, the formulas differ for linear $(n = 3N - 5)$ and non-linear $(n = 3N - 6)$ molecules, where $n$ is number of modes and $N$ is number ...
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2answers
5k views

Why do some things crystallize? (And others don't, for that matter.)

Ice, for example, will form a crystal when frozen under certain circumstances. Why is this the case for ice? While on the subject of water crystallization, why do snowflakes usually form in base 6 ...
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3answers
4k 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 ...
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5answers
676 views

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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4answers
1k views

The “binding energy” of bonded particles adds mass?

This is a follow-up my previous question. Several of the answers indicated that the mass of a particle (atom, proton, etc.) increase with the "binding energy" of it's component particles - the energy ...
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2answers
4k views

How do I integrate the Poisson equation to determine the electric potential along a particular direction (e.g., $z$)?

This question is a sequel of sorts to my earlier (resolved) question about a recent paper. In the paper, the authors performed molecular dynamics (MD) simulations of parallel-plate supercapacitors, ...
4
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1answer
632 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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5answers
11k views

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 ...
2
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2answers
192 views

Is there anyway to use a scientific instrument to measure the density of electron around the atomic orbital?

Is there anyway to use a scientific instrument to measure the density of electron around the atomic orbital? Please list both old way and more modern ways.
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3answers
186 views

Why is methane considered an important greenhouse gas?

Methane’s absorption bands are centered at 3.2 and 7.2 microns -- far off the peak of the Planck spectrum for a 290 K blackbody near 16 microns. Moreover, its absorption bands overlap with the water ...
2
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4answers
741 views

Two soft questions about spin and the particle nature of electrons

How can we define spin as the spin of an electron around it's own axis if an electron is described by a probability cloud of finding an electron in a point in space? How does that probability cloud ...
2
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1answer
1k views

Conductivity of Aqueous Ionic Solutions as a Function of Time

It is well-known that an aqueous ionic solution can conduct electricity. Let's take the electrolyte NaCl for example. In the diagram below, the circuit consists of a voltage source, a light bulb, and ...
2
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1answer
182 views

Why does sunlight cause colors to fade?

If you leave something outside, its colors seem to inevitably fade or bleach due to exposure. Is this due to UV absorption? What sort of mechanism causes this - is it that man-made dyes deform on a ...
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1answer
137 views

How does an infinitely hard tip scratch an amorphous brittle material when it slides along it?

I know infinitely hard materials don't actually exist but sometimes the tip is so much harder than the substance it's scratching that it can be treated like one. Suppose a sharp diamond tip is made to ...
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4answers
2k views

How does the dissolution of salt affect the solution density?

Suppose you have a container of water as a solvent and you a certain amount of salt as a solute sitting at the bottom of the container that has yet to start dissolving. Supposing temperature and ...
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0answers
29 views

Bond energy and tempetature

Does bond energy depend on temperature? Also why is it defined at 298 Kelvin if some substances cant be in gas phase in that temperature?
119
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2answers
11k views

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 ...
33
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5answers
1k 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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5answers
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In a Monte Carlo $NVT $simulation how do I determine equilibration?

I'm running an NVT (constant number of particles, volume and temperature) Monte Carlo simulation (Metropolis algorithm) of particles in two dimensions interacting via Lennard-Jonse potential ($U = 4(\...
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5answers
9k views

Can a radioactive atom be prevented from decaying if it's in a REALLY strong chemical bond?

So, based on this question, a molecule containing a radioactive atom will break when the atom decays. But suppose you need a lot energy to break the compound apart --- as in, more energy than the ...
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6answers
44k 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 ...
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9answers
3k views

Were alchemists right? [closed]

When I was in school, I learned about alchemists, a group of scientists who sought a way to convert other materials into gold. They were never successful, so whenever I studied or read about them, ...
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4answers
7k 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., ~1,...
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1answer
6k views

Why doesn't soda go flat immediately after opening?

So, soda is under pressure and has gas dissolved in it. But, when you open it, the gas is still dissolved in it. But, if we wait a few hours, the gas has escaped into the atmosphere. What factors ...
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3answers
5k views

Why is the ideal gas law only valid for hydrogen?

I got this question in school: Explain, based on the properties of an ideal gas, why the ideal gas law only gives good results for hydrogen. We know that the ideal gas law is $$P\cdot V=n\cdot R\...
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3answers
6k 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 ...
15
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2answers
628 views

Implications of parity violation for molecular biology

In biology, the concept of parity emerges in the context of chiral molecules, where two molecules exist with the same structure but opposite parity. Interestingly, one enantiomer often strongly ...
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2answers
3k views

Why heavy elements don't sink to the core?

If earth assembled out of space dust, how come we find heavy elements like gold, silver, uranium and bunch of others that are heavier than iron on the surface? I mean silicon (Si mass 28.084) being ...
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3answers
949 views

Why does ice melt, wait for 100 degrees and THEN vaporise? Why is not the process of expansion of things continuous?

What I am asking is this: Why can't a body be solid, then solid-ish, then solid-like, then liquid-like, then liquid-ish, then liquid, then vapor-like and then vapor? Why is there a rigid temperature ...
6
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1answer
4k views

What is the most stable nuclide of an isobar?

From the semi-empirical mass formula, the mass of an atomic nucleus is $$M\left(A,Z\right)=Zm_p+(A-Z)m_n-\frac{E_b(A,Z)}{c^2}$$ I've been told (at first) that for a given mass number $A$, the most ...