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Question: Can $\ce{SiO2}$ melt at $\pu{20 ^\circ C}$? According to experimental and calculated data values, my answer is no. See the phase diagram of pure silica based on the experimental and calculated data given in Ref.1: Reference 1 states that: An internally consistent data set on the thermodynamic properties of the silica polymorphs stable up to $\pu{...


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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 (...


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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 much ...


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, ...


5

Depending whether you have a molecular, metallic or ionic compound, the independently moving particles in the liquid state are molecules, atoms and ions, respectively. So for a molecular solid, you have to break the intermolecular forces to turn it into a liquid (or make them non-persistent so that the interaction partners can change over time). For a ...


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

Water loses kinetic energy when it detaches from the surface of the ice Water molecule in the solid phase have more hydrogen bonds than in the liquid phase. It takes energy to break these bonds, so only molecules with sufficient kinetic energy will detach (maybe because they just collided with a water molecule that transferred some kinetic energy to it). So ...


3

This is a summary of the equations to use to calculate phase transitions. The Clapeyron equation $\displaystyle p_2-p_1=\frac{\Delta H}{\Delta V}\ln\left( \frac{T_2}{T_1} \right)$ is used for a solid-liquid transition. The changes in enthalpy and volume relate therefore to changes occurring in fusion. The Clausius-Clapeyron equation describes solid-vapour ...


2

Remember that temperature is a macroscopic quantity, telling the heat content of system. So if the crystalline solid is at its fusion temperature, and every atom in the crystals have equal interaction energy with each other (ignoring all defects of lattice), the whole solid should fuse simultaneously, thus having sharp melting point. On the other hand, ...


2

As noted, chemistry is an experimental science. That being so, experimental data allow for a few rules. Given that salts are often formed from reactions of acids and bases, we should not be surprised to see acid-base chemistry enter into these considerations. 1) Salts with three or more elements are more likely to decompose than those that are only ...


2

When a substance is made of molecules, these molecules are made of atoms being strongly attached to one another. But a given molecule is not attached to its neighbor by strong bonds. On the contrary, they are attached by so-called van der Waals forces, which are rather weak. If you heat such a substance, the van der Waals forces are easy to destroy, and the ...


2

TL.DR: Aluminium oxide (sometimes known as alumina) is made by heating the aluminium hydroxide to a temperature of about 1100 - 1200°C. (Chemguide) $$\ce{Al(OH)3 ->[\Delta] Al2O3 + 3H2O}$$ As @andselisk said, the temperature Wikipedia mentions is aluminium hydroxide mixture in a fire retardant which might have other compounds. Decomposition of pure ...


1

why is it that metal groups decrease in melting points going down This isn't quite true for all metals. I think the only metals that behave like like this are the alkali metals. Group 6 metals increase in melting point. Calcium has a higher melting point than Magnesium. Etc. more shells exist thus ions in the lattice will be larger so more IMFs ...


1

Reason 1: For example if you have an porous ore and you melt it, the surface area will decrease dramatically. If you just roast it, the surface area will stay about the same. A higher surface area will aid calcination proceses as more oxygen gets into contact with the surface and will eventually react. Reason 2: A higher temperature means more energy to ...


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There are multiple reasons why things don't melt The biggest chemical explanation of why some substances don't melt is that many decompose instead. This is true for many complex organics like paper. IF you add enough energy to (theoretically) melt them you have already added enough to shake the component molecules apart. This is true whether or not they are ...


1

The lignin, and some of the hemicelluloses, in wood can melt under certain circumstances, such as friction welding. For a dramatic video, see: https://www.facebook.com/interestingengineering/videos/1891004754302553/ See also: http://web.utk.edu/~mtaylo29/pages/Wood%20welding.htm?fbclid=IwAR1MLgBtkfESlYiaP0iEaXbv36AtLy8yXEj0iCqFaaVYBcDRitxqeZJZYtM Here ...


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