81 votes

How is water heavier than petrol, even though its molecular weight is less than petrol?

Density relates to the mass per unit volume. If your molecules are heavier but take up more space, the net result could be more or less mass per unit volume. When you look at a typical hydrocarbon, ...
Floris's user avatar
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80 votes
Accepted

How is water heavier than petrol, even though its molecular weight is less than petrol?

Because water molecules are small and pack tightly together, causing water to have a greater density than petrol.
G. Smith's user avatar
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50 votes
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Is sound a classical mechanic phenomenon or is it a quantum effect?

The detailed physics of sound wave transmission through air were mathematically worked out and found to be accurate before the invention of QM. No quantum-mechanical effects need to be taken into ...
niels nielsen's user avatar
45 votes
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Are water molecules orientation absolutely independent of the flow direction?

These types of questions are tempting to ask in a yes-no way, and you currently have an answer that says "yes" and and answer that says "no." The physicist's approach is to ask how ...
rob's user avatar
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42 votes
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Why isn't the molecule of water linear straight?

There are six electrons in the outer orbital of an oxygen atom. In a water molecule two of these electrons bond with the lone electron of each hydrogen atom to form two “bond pairs”. The remaining ...
gandalf61's user avatar
  • 50.3k
39 votes

Is it heat that causes vibrations on particles or is it the vibrations that causes the heat?

The fancy word terminology for this is that the concept of heat supervenes on the concept of molecules moving. We can think about heat as molecules moving. We can also think about a lot of non-heat ...
Cort Ammon's user avatar
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36 votes
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Is it possible to obtain antiwater from antihydrogen and antioxygen atoms? And how is its property w.r.t. the ordinary water?

Research has created antihydrogen, and that is about it for the present as far as antimatter in bulk, which one would need for antiwater.. Scientists in the US produced a clutch of antihelium ...
anna v's user avatar
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36 votes
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Why is it so much more energy intensive to compress hydrogen than methane?

The essential reason is that a kilogram of hydrogen contains 8 times as many molecules as a kilogram of methane (because the mass of a hydrogen molecule is about 1/8 of the mass of a methane molecule)...
Philip Wood's user avatar
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36 votes
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When two molecules collide, does it produce a sound?

A sound wave is a synchronised movement of millions and millions of atoms or molecules. The random collisions of atoms or molecules are not synchronised and do not produce a sound wave. A sound wave ...
gandalf61's user avatar
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30 votes
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Since water is a molecule, can the aerosol sprayed through double slit form interference pattern?

No, not with a spray. The reason for this is that "sprays" are not isolated molecules. They are fine droplets, and the individual droplets are still vastly larger than a molecule - a ...
The_Sympathizer's user avatar
29 votes

Is it possible to obtain antiwater from antihydrogen and antioxygen atoms? And how is its property w.r.t. the ordinary water?

Anti-matter is a lot less exciting than you probably think. If we could magically change all matter to anti-matter by waving a magic wand then it would make almost no difference. The anti-Dirk could ...
John Rennie's user avatar
28 votes
Accepted

Is Avogadro's law applicable for atoms or just for molecules?

I notice that online definitions of this experimental law always say, molecules or atoms. The problem with just calling them all "molecules" and being done with it is some are uncomfortable with ...
BowlOfRed's user avatar
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23 votes

Can a single molecule have a temperature?

Without intending any disrespect, I'm quite surprised that several very knowledgeable people have given a wrong, or at least incomplete, answer to this old question. For a single molecule that is in ...
Rococo's user avatar
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22 votes

Why isn't the molecule of water linear straight?

Let's start by taking a look at the 'bare' oxygen atom. While simplistic depictions of atoms often show the electrons orbiting the nucleus on various circular orbits as if they were planets, quantum ...
Jan's user avatar
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20 votes
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Is water really $H_2O$? On a comment concerning the quantum mechanical description of water made by Hilary Putnam

I'm not sure I would have phrased it exactly that way, but I think his statement is by-and-large defensible. The crux of the issue is that, in liquid water, there is no sharp line between ...
Steve Byrnes's user avatar
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20 votes
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Implications of parity violation for molecular biology

The idea that there must be some reason that all terrestrial DNA has a right-handed twist (or D- vs. L-glucose, or whatever your favorite chiral biomolecule is), goes all the way back to the discovery ...
rob's user avatar
  • 88.6k
20 votes

How does removing air from a vessel of water create bubbles?

Basically, oxygen and nitrogen, like carbon dioxide, are soluble in water. The higher the pressure in the water, the more soluble they are. Remove the pressure and they come out of solution, in the ...
TimWescott's user avatar
  • 2,781
19 votes

Is sound a classical mechanic phenomenon or is it a quantum effect?

Well, niels answer is correct of course. Sometimes you can have also sound in QM system, it is called phonons where a mechanical classical vibration is traveling along the atomic lattice of some ...
Markoul11's user avatar
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16 votes
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Why doesn't the ${\rm H}_2$ molecule have a permanent dipole while the neutral ${\rm H}\,{\rm\small I}$ has one?

$H_2$ contains 2 electrons in the same ground-state orbital; by Pauli exclusion, one must be spin-up and the other must be spin-down. The 21cm line is generated in a normal hydrogen atom when an ...
probably_someone's user avatar
16 votes

Why is carbon dioxide a non-polar molecule?

Yes it is about the partial charges on the atoms but the dipole is a vector not just the charge distribution which is positive in the center and negative on the O's but the vectors cancel
ChemEng's user avatar
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15 votes

Is water really $H_2O$? On a comment concerning the quantum mechanical description of water made by Hilary Putnam

I think it's tosh. A very small fraction of liquid $\rm H_2O$ will spontaneously decompose and recombine with very small amount of $\rm H_3O^+ $ (hydronium ion) and $\rm OH^-$ (hydroxyl) ions. Weak ...
Charles E. Grant's user avatar
14 votes

Why is $\text{CO}$ a good tracer for $\text{H}_2$? How are those molecules correlated?

Answering this question inevitably leads to stumble upon one of the most controversial topics in astronomy. First let’s give some context here by reminding why tracers of $\mathrm{H_2}$ are required ...
Gonstasp's user avatar
  • 1,287
14 votes

Is it heat that causes vibrations on particles or is it the vibrations that causes the heat?

It's both: At the smallest scale, thermal energy is just kinetic energy, the energy of motion. That is, thermal energy (heating up) and kinetic energy are the same thing. When molecules vibrate, ...
AmagicalFishy's user avatar
14 votes

Is sound a classical mechanic phenomenon or is it a quantum effect?

Sound is successfully described using continuum mechanics of solids and liquids (that is the theory of elasticity and hydrodynamics). That is, one need not even descend to the level of molecules/atoms,...
Roger V.'s user avatar
  • 58.2k
14 votes

Are water molecules at the surface closer or farther apart than the molecules inside?

The usual attempt to explain surface tension shows two molecules in a surface and in the bulk, where the surface molecule only experiences attractive forces from one side, while the bulk molecule ...
oliver's user avatar
  • 7,432
12 votes

Can you make a metal denser by melting it and make it cool down under high pressure?

First of all, high pressure (i.e., compressive equitriaxial stress) is simply not going to induce cracks (or failure of any sort) in a uniform solid—there's just nowhere for the material to move to ...
Chemomechanics's user avatar
12 votes

Why is carbon dioxide a non-polar molecule?

The difficulty might be due to nomenclature : How is polarity defined? In physics the electric field of any distribution of charges can be decomposed into a series of electric multipole moments. The ...
sammy gerbil's user avatar
  • 27.2k
12 votes
Accepted

Energy of molecular vibrations

It does depend on the mass, but mass it is not explicit in the equation $$E_n=(n+\frac12)\hbar\omega$$ but it is implicit. In the equation above we have the vibrational frequency $$\omega=\sqrt{\frac{...
joseph h's user avatar
  • 29.1k
12 votes

Why isn’t $\rm H_2 O$ a primordial element?

The only chemical elements created in during the Big Bang are hydrogen (H), helium (He) and lithium (Li). This phenomenon is called Big Bang nucleosynthesis and current theories predict very well the ...
Mauricio's user avatar
  • 4,957
11 votes

Since water is a molecule, can the aerosol sprayed through double slit form interference pattern?

The deBroglie wavelength of a droplet of water can be calculated like any other particle: $$\lambda = \frac{h}{mv}$$ Where $h = 6.62607015×10^{-34} \frac{J}{Hz}$ - at $100 \frac{m}{s}$ a 1000 nm ...
Yakk's user avatar
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