78

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, it has a lot of carbon and hydrogen. Now atom for atom, oxygen is heavier than carbon (ignoring isotopic abundance, roughly a 16:12 ratio). So if the molecules ...


74

Because water molecules are small and pack tightly together, causing water to have a greater density than petrol.


7

There are two ways to have absolutely forbidden transitions, one rigorous, the other only valid in the thermodynamic limit. One class of forbidden transitions is those that violate conservation of a conserved quantity. In practice, the only absolutely conserved quantities are the (locally conserved) gauge charges of the electromagnetic, strong, and ...


6

[Note that this is an answer to an earlier version of the question.] It is not possible to see either gas: what you are seeing is soot: small particles of carbon suspended in the air. The reason that soot is associated with CO in everyday life is that both are produced in situations where burning/oxidation is incomplete. So an engine burning petrol (say) ...


5

Regardless of energy state, regardless of the choice of isotope, if we have two identical atoms in this molecule (i.e. same isotope of oxygen), this pair must have even numbers of all nucleons and electrons. This then precludes half-integer total spin, which leads to bosonic properties of the system. I initially thought a light (photon) can excite the ...


5

Has any scientist practically confirmed that H2O molecules vibrate... Yes, molecular vibration and rotation can be measured using Raman Spectroscopy. when heat energy is provided to them? And yes, the population in rotationally/vibrationally excited states depends on the temperature of the molecules. You can see some nice spectra of this here. Side ...


3

One of my Chemistry teachers had an interesting way to describe this type of phenomenon. Because the water molecule is shaped like a triangle, it is possible for the water molecules to "snuggle up" with each other, and pack themselves close together. Like this: >>>>>>>>> He claimed that Water molecules behave more like H(100) O(50) that H(2) O. Now, I'm ...


3

The answer here is that color is not a property of elements alone, but rather of the structures formed from them. Graphite, soot, and carbon (mon/di)oxide are all different kinds of structures, despite all being made of, or at least containing, carbon, and thus are under no obligation to be all the same color. Even pure carbon has a structure - diamond - ...


3

In simple terms Chlorine is more electronegative than Hydrogen. In combination this results in the Chlorine distorting the electron orbitals resulting in a slight residual positive charge in the region of the hydrogen nucleus and a slight residual negative charge in the region of the Chlorine nucleus. The Chlorine has a greater share of an electron than ...


3

O3 is less stable compared to O2 ( Positive gibbs free energy) . In the upper layers of atmosphere it is constantly generated by UV radiation falling on O2 gas , thus though it dissociates into O2 , it is continuously being generated also. As we come down , rate of generation falls and hence O3 concentration falls too.If O3 tries to fall it will decompose to ...


2

Although the size of the molecules are still the same, the oil (nonpolar) cannot dissolve into the water (polar), so the oil drops form inside water, which is much larger than the molecule itself. Those drops (emulsion) reflects light and causes tyndall effect.


2

The bond is not 100% ionic, but rather covalent with a difference in electronegativity of about 0.9 thus you don't have an H that has become $H^+$ (a proton). There are only partial partial charges on both atoms $H^{\delta +}$ and $Cl^{\delta -}$ with $\delta^+= 3.4 \cdot 10^{-20} C$


2

Your question is a good one, though it's somewhat unclear. I think what you're asking, in essence, is whether one needs quantum mechanics to accurately model the activity of proteins, or whether classical physics is sufficient. If one takes the proteins as already existing, the answer, in the vast majority of cases, is that classical mechanics is sufficient. ...


2

This is a partial answer. There is a class of proteins called enzymes. Enzymes facilitate chemical reactions. Many enzymes facilitate in the following way: a particular small region of the enzyme has a high affinity for a particular molecule. That is, when that molecule comes in contact with that active region it tends to get stuck there. The fit is good, ...


2

Quantum mechanics as a theory was invented in order to explain why classical mechanics and classical electrodynamics did not work in certain situations: small scales, spectra of atoms , black body radiation. Classical mechanics and classical electrodynamics cannot explain or predict the behavior of atoms (their interactions) , neither that of ...


2

Motion in any direction would be a combination of motions in three perpendicular directions $x,y,z$. Similarly, rotation around any axis can be regarded as a combination of three rotations around $x,y,z$. That is why you don't need to count other directions.


2

A degree of freedom in this context is a quadratic term in energy. The translational kinetic energy for a free particle in 3D is $p^2/2m = (p_x^2 + p_y^2 + p_z^2)/2m$, three quadratic terms. A diatomic has two vibrational degrees of freedom (at sufficiently high temperatures): one for kinetic energy and one for potential energy.


2

The uncertainty principle is also related to the kinetic energy of an electron. The hydrogen atom confines the electron to a small sphere with an average radius of $0.5$ angstroms. If you restrict the accessible space of the electron to a smaller average distance from the nucleus, say $0.3$ angstroms, then the kinetic energy will increase dramatically, as ...


2

In a live game being broadcast by radio or television waves, the signals will reach you at the speed of light. Anything you could do to the air molecules could travel no faster than the speed of sound, which is much slower than light. The game would most likely be over before any atmospheric effects could reach there. So, unless you interacted with the game ...


2

Believe what you may, the sentence I believe that that standard for making calculations can be simplified to another standard that gives rise to an entirely different simplified quantum mechanical theory that doesn't talk about nuclear chemistry at all that can explain hybridization of orbitals and wave functions and is relativistic. is unlikely to be ...


1

It's a flat ground, so it can't cause any sideward force. But the water still moves. Whats going on here? The defining property of a fluid is that the shear stress is proportional to the shear rate. This means that if you have two parallel plates separated by a layer of fluid then the force required to slide the plates (shear stress) is proportional to how ...


1

The states of the hydrogen molecule come from the molecular Hamiltonian, not a combination of the atomic states. Molecular orbital theory uses the Born-Oppenheimer approximation and the atomic orbitals to get approximate electronic states (for H2). The states are not necessarily entangled, except in the trivial antisymmetric sense. But that probably isn't ...


1

The rule is simple: A combination of particles is a fermion is it contains an odd number of fermions otherwise it is boson. Since $\text{O}_2$ is two of the same particle (assuming both are the same isotope), it is necessarily bosonic.


1

Because gas is compressible, you must specify its pressure along with the volume it happens to occupy in order to properly define its state. And since heating a gas causes its pressure to increase, a complete description of any gas will necessarily include calling out its temperature as well. Since more gas atoms in a fixed volume will exert more pressure ...


1

If you are considering a gas/partial vacuum that is not confined in a well-defined 'container', you would presumably want use specific volume (aka inverse density) instead. I.e. consider the amount of volume occupied per unit mass of the substance.


1

A photon has momentum $\mathbf{p} = \hbar\mathbf{k}$. This is a vector, so by conservation of momentum, the molecule has to gain momentum $m\mathbf{v} = \hbar\mathbf{k}$ in the proper direction. During absorption, the energy $hf$ of the incident photon is split in two (or more if there's rotation and vibrations, but let's keep it simple): $hf = \frac{1}{2}...


1

Let's take water (and air) as an example. Sound is a vibration that typically propagates as an audible wave of pressure, through a transmission medium (air and water in you example). At the QM level, the vibrational energies of the water molecules could be interpreted as heat (temperature). Molecules, such as oxygen (O2), have more degrees of ...


1

Since the "mean positions" of the positive and negative charge are different, the magnitude of the force they exert on the other molecule is not the same. Hence they don't cancel out and the other molecule is acted upon by a net non-zero force. In the water molecule, the electronegativity of the $O$ atom and the $H$ atoms differ, oxygen being more ...


1

Another approach to answer this for youself might be to run with the idea and look at molecules with even higher molecular weight. Like, why aren't plastics far heavier than lead? Why isn't DNA? These are truly massive molecules, yet their densities are pretty low (comparable to water). With polymers, you should pretty quickly get the idea, that the ...


1

There is a certain amount of New Age mythology about stones & crystals,but the good vibes they give off are purely imaginary. Some crystals,ruby for example, can be used for Light Amplification by Stimulated Emission of Radiation,or lasers,but it's nothing to do with sound. Military research has experimented with using sound (or ultra-sound) as a weapon,...


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