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Honey is indeed a complex mixture containing more than hundred compounds. As for Wikipedia and depending on the point of view it is a supersatured liquid solution a viscous supercooled liquid (in the sense that it can get so viscous as to appear solid, without affecting its status of being a supersatured solution, and undergoes glass transition). https://...


19

Wolfram company doesn't conduct any experimental determinations of physical constants for chemical compounds and uses literature data sources. The webpage for ChemicalData Source Information lists numerous sources of chemical information used by the company's products, including Wolfram Alpha. Wolfram Alpha Knowledge Database is linked with 87th ed. (2006) ...


16

Melting and dissolving are all the same when you look at mixtures close to saturation. You can say water lowers the melting point of the sugar, or that the solubility of sugar increases with temperature. Different description, same fact. What makes this seem different from e.g. a salt water solution is that the molten (i.e. non-crystalline) sugar is fully ...


9

The CRC Handbook of Chemistry and Physics ($\mathrm{86^{th} Ed.}$, section on Physical Constants of Organic Compounds) provides an MP of $\pu{135^\circ C}$ for aspirin (2-(Acetyloxy)benzoic acid). According to the Handbook: The data in the table have been derived from many sources, including both the primary literature and evaluated compilations. If ...


7

In stereochemical vocabulary, a racemic mixture (racemate) is one that has equal amounts (50:50) of left- and right-handed ($d$- and $l$-) enantiomers of a chiral molecule. According to Wikipedia: Racemic Mixture, a racemic mixture can be crystallized in four ways: Conglomerate (sometimes racemic conglomerate): If the molecules of the substance have a ...


7

If solid menthol were just amorphous, then you would expect the racemate and each enantiomer to exhibit identical melting points. However, if you read further on the Wikipedia page you reference, you'll see that racemic vs. enantiopure menthol crystallizes differently: The two crystal forms for racemic menthol have melting points of 28 °C and 38 °C. Pure (...


6

I think what you are asking is this: Equilibria for chemical reactions typically* (see note at end) require specific ratios of products to reactants (as expressed by the equilibrium constant). By contrast, equilibria for phase transitions don't require specific ratios of products to reactants. [For instance, at the phase transition between ice and water, ...


6

According to the Carnelley’s Rule: That of two or more isomeric compounds, those whose atoms are the more symmetrically and the more compactly arranged melt higher than those in which the atomic arrangement is asymmetrical or in the form of long chains If we attend to the structure of the 1,1-dimethylhydrazine, one can see that the steric hindrance ...


4

At low concentrations for which the ideal bp elevation/fp depression expressions usually apply, molarity is linearly proportional to molality, therefore the statements are equivalent. This webpage explains nicely why low concentrations are important: Raoult's law only works for low concentration solutions. Why? Well, in order for our approximation to ...


4

For your interest, I quote a paragraph from a book "Handbook of Nanophysics: Nanoparticles and Quantum Dots" by Klaus D. Sattler (Ed.). Section 12-8. I don't think people know the reason as to why Ga likes to exist as a dimer (as you know $\ce{S}$ is $\ce{S8}$ and so on). The cohesive energy of the elemental solids is defined as the difference between ...


4

This table indicates that polyethylene (HD/LD not specified) "melts at" 135°C, decomposes in the range 335-450°C, and produces vapors that will ignite between 341-357°C. I'm sure melting/softening temperature is more complex than that, but I'm not sure that you should expect much decomposition into toxic gases at temperatures below 260°C. However, if you'...


3

[OP] Why are melting and boiling considered equilibrium processes [...] They should not be considered equilibrium processes. If melting is defined as the process where there is a net change from solid to liquid phase, this is not an equilibrium. If boiling is defined as the process where liquid turns into vapor (rolling boil with bubbles forming below the ...


3

Two different phases of a substance in contact with each other in a closed system at some uniform temperature and pressure (thermal and mechanical equilibrium) will be in equilibrium if the chemical potential of the substance is the same in both phases. It turns out that at its boiling point, a liquid has the same chemical potential as its vapor at that ...


3

The effect of intramolecular forces versus intermolecular forces on boiling and melting points is sometimes seen when we compare the boiling points of ortho- and para-nitrophenol (or similar compounds). Para-nitrophenol shows intermolecular hydrogen bonding, which causes an increase in boiling point as different molecules bond better with each other, as ...


3

It's possible that the gallium is not as pure as advertised. If it has (say) some indium as an impurity, the indium-gallium alloy would have a lower melting point, potentially below room temperature. I thought that partial freezing might have crystallized out more pure gallium, and left less pure gallium as the melt, but I'm not sure that's how indium-...


2

One way is to use electristatic or electromagnetic forces to hold the liquud in place. This abstract refers to a "non-contact method" and an "electrostatic levitate", which us enough to reveal the basic strategy. Unfortunately the article is behind a paywall, so you have to put up to get details on the good stuff. Industrially, metals like tungsten are ...


2

This is a tough question to answer because the intermolecular distances are similar in the solid to liquid transition unlike those in the liquid to gas phase transition. In the case of the elements there is a correlation between the Debye temperature and the melting temperature. The Debye temperature is that temperature at which the atoms gain their full ...


2

Melting points of related compounds: hydrazine, 2 °C; monomethylhydrazine, −52 °C (Wikipedia). Three of the four compounds have an $\ce{NH2}$ group, so this is not a deciding factor. Hydrogen bonding may be present without being a factor in the different melting points. The common feature in the two high-melting compounds is a symmetrical N-N bond; an ...


2

You are absolutely right about suspecting the reliability of sources, based on their value spread. I think, I found what's going on with those internet (I assumed) sources. Yet, I know everybody agree with me that CRC handbook of chemistry and physics is The Bible for Physical Constants of Organic Compounds. Here is what I found on 2005 Internet Version of ...


1

Metallic bonding is a type of chemical bonding that rises from the electrostatic attractive force between conduction electrons (in the form of an electron cloud of delocalized electrons) and positively charged metal ions Van der Waals forces include attraction and repulsions between atoms, molecules, and surfaces, as well as other intermolecular forces. The ...


1

Wikipedia disagrees with your figures. They give a melting point only for the pentahydrate (18°C, at which point this forms not pure sodium hypochlirite but a solution of one mole sodium hypochlirite to five moles water). The only reported phase transition for the neat compound is a "boiling point" of 101°C which is actually a decomposition point. So I ...


1

Polar or flexible molecules tend to have a liquid phase also at low pressures, so do metals. Rigid, unpolar particles not (naphtalene, helium, iodine). The difference makes wether a not perfectly ordered phase still can have enough intermolecular forces to keep it in a condensed (=liquid) state. A molten metal is likely still metallic. Hydrogen bonds in ...


1

From a thermodynamic point of view there are two competing possibilities for condensation of a vapor: (1) vapor $\ce{->}$ liquid, with some negative $\Delta H$ (2) vapor $\ce{->}$ solid, with an absolutely larger negative $\Delta H$ In the absence of large quantum mechanical effects (see here), the second process with a more negative enthalpy change ...


1

Here is a simple minded answer. High melting point compounds tend to follow the octet rule - the number of valence electrons sums to 8. The Group IVB carbides (TiC, ZrC, HfC) have an 8 electron sum (4+4) and have very high melting points - for HfC it is approximately 7100F. The Group IIIB nitrides and phosphides have an 8 electron sum (3+5) and are the ...


1

The reason for cooling is related to solubility at different temperatures not melting point The reason many precipitation reactions cool the solution to generate a precipitate (or to maximise the yield of it) is because the solubility of most substances in most solvents decrease with temperature. For those substances where the solubility is much lower at ...


1

It's a complicated problem and I'm going to add a hand-waving physics answer. For most materials, at a given wavelength the albedo and and emissivity sum to roughly unity. So if something is close to white with an albedo of 0.9, it's emissivity in the visible range is about 0.1, and if something is dark, those are reversed with albedo ~0.1 and emissivity ~0....


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