30 votes

Why is the boiling point of fluorine lower than that of oxygen?

It would be tempting to argue that fluorine is so electronegative and holds its electrons so tightly that their polarizability is reduced, thus so are the dispersion forces in $\ce{F2}$. But upon ...
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23 votes
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Alkane, alkene, alkyne boiling point comparison

Disclaimer: All of this "jazz" will be about reaching a mere rule-of-thumb. You can't just compare whole families of organic compounds with each other. There are more factors to consider than below, ...
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21 votes
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Why do cyclic hydrocarbons have higher boiling points than their acyclic isomers?

Your intuition is indeed correct! Several sources provide the same answer (1, 2, 3). Perhaps the simplest and most direct evidence comes from comparing the densities of the liquid unbranched alkanes ...
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21 votes
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Why is the boiling point of stibane higher than that of ammonia?

Though it does go against your intuition, you've actually mentioned the answer in your question. Stibane has a higher boiling point than ammonia/azane on account of van der Waals interactions (owing ...
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20 votes

Justification for Freezing Point Depression & Boiling Point Elevation in Solutions?

I think you are looking at the problem from slightly the wrong angle. The central quantity when dealing with colligative properties is entropy and not solute-solvent or solvent-solvent molecule ...
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19 votes

Why do the melting and boiling points of the noble gases increase when the atomic number increases?

The melting and boiling points of noble gases are very low in comparison to those of other substances of comparable atomic and molecular masses. This indicates that only weak van der Waals forces or ...
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18 votes
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Boiling and melting point of trans- and cis-but-2-ene

Yes . You are right that structural symmetry comes into play . Boiling point depends upon intermolecular interactions which over here is more in cis due to its net dipole moment . The dipole ...
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  • 2,107
17 votes

Which substance has the highest temperature range between melting and boiling point

Gallium melts at 30 °C but doesn't boil until 2200 °C. If 30 °C is a bit too warm to count as "room temperature" or "normally" for you, I found an old paper that recommends tetralkyl ...
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17 votes

Enrichment of D2O

Fractional distillation can work, but the separation per round of distillation is very low so you would need a very large multi stage process to achieve significant separation. Nobody uses direct ...
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16 votes
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Boil to dry 50 liters water

What actually happens in real life depends on a lot of things. Factors like the shape of the pot can make a big difference to how much of that 2500 W actually goes into vaporizing the water and how ...
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15 votes

How much salt (or any other substance one can find in a kitchen) do I need to add to make water boil at 104 °C?

According to [1, pp. 281–282], solution of sodium chloride $\ce{NaCl}$ prepared by dissolving 25 g of salt in 100 g of water has boiling point of 104.6 °C. Additional data is available in the ...
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14 votes
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400–430 degrees Celsius heated bath

If it doesn't specifically need to be a hydrocarbon, zinc metal melts at 419.5 °C. Could you do an "ice bath" of zinc chunks in molten zinc, maintaining the melt right at its melting point?
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  • 1,482
13 votes

Why do cyclic hydrocarbons have higher boiling points than their acyclic isomers?

I agree with the points made above regarding attractive forces in the liquid being diminished in the gas phase. However, I also think there may be an entropic component to all of this. When a ...
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12 votes

Will gaseous ionic compounds be free moving ions?

To complete the previous answers: according to this article http://www.ncbi.nlm.nih.gov/pubmed/17579381 NaCl exists in the gas phase both as a monomer (NaCl), about 73% of atoms at 943K, and as a ...
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  • 2,677
12 votes
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Which substance has the highest temperature range between melting and boiling point

The polar aprotic solvents (for example dimethylformamide, mp −61 °C, bp 153 °C, or hexamethylphosphoramide, mp 7 °C, bp 230–232 °C) would be a place to start. Silicone oil is often used in heating ...
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  • 9,006
11 votes
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Arrange these compounds: CO2, CH3OH, RbF, CH3Br in order of increasing boiling points

You know $\ce{CO_2}$ is gaseous at room temperature, so let's put that at the bottom. Methanol forms hydrogen bonds, so that will be above bromomethane which does not. At last we have rubidium ...
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11 votes
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Why do cyclic ethers have higher boiling points than their acyclic isomers?

The data I could find suggests that cyclic ethers have higher dipole moments than their acyclic counterparts. $$\mathbf{Four~carbons}$$ \begin{array}{c @{} c} \hline \text{THF} & \mathrm{1.63~ D ...
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11 votes
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At what temperature (in kelvin) are most of the elements on the periodic table liquids?

Now that's a great question indeed! Evidently, at 0K all elements except helium are solids, at 10000K they are all gases, so someplace in between the number of liquids must reach a maximum; what and ...
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11 votes
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Does the temperature of liquid ammonia stored at high pressure, room temperature suddenly drop to −33.35 °C when poured into a bowl?

The key to understanding what happens is that evaporation costs energy. Changing the state of a liquid to a gas requires the input of energy: this is basic thermodynamics. This is in addition to any ...
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11 votes
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Confusion over boiling point of gallium

This question has been recently raised in Chemistry & Engineering Letters. The CRC Handbook (2017) in section "MELTING, BOILING, TRIPLE, AND CRITICAL POINTS OF THE ELEMENTS" [1, p. 4-117] lists ...
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10 votes
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How is it possible for a substance to have a high heat of vaporization but a low boiling point?

This seeming contradiction can be reconciled by examining the thermodynamic quantities involved. First, per Wikipedia, the enthalpy of vaporization is "the enthalpy change required to transform a ...
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9 votes
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Caffeine boiling and melting points

Anhydrous caffeine occurs in two different polymorphic crystal forms, with a transition between the two forms occurring at $\pu{136 °C}.$ The high temperature form has a melting point of $\pu{236 °C}.$...
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9 votes

Which substance has the highest temperature range between melting and boiling point

A good place for a general list is http://www.engineeringtoolbox.com/melting-boiling-temperatures-d_390.html For high temperatures, here is a list of alloys https://en.wikipedia.org/wiki/...
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9 votes

Why do the boiling and melting points decrease as you go down group 1 and vice versa for group 7?

The group 1 elements are the so-called alkali-metals. The bonding between the atoms is caused by the interaction of the nuclei with the delocalized electrons. With increasing number of electrons and ...
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9 votes

Elevated boiling points in alkanes with even number of carbons

There is not really any difference between the boiling points of even and odd carbon alkanes. For single-chain alkanes the boiling point just goes up as a smooth curve versus chain length. The ...
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  • 38.1k
9 votes

How to compare the boiling point of water, ammonia and hydrogen fluoride?

Though ammonia has three H atoms, it is not capable of forming four H-bonds An important difference in terms of hydrogen bonding between ammonia and water, lies in the ratio between how many partial ...
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9 votes

Any examples of liquids volatile at room temp but non-flammable?

Yes, there are lots. Start with Wikipedia's list of refrigerants; while it doesn't call out flammability, any fully-halogenated compounds will be effectively non-flammable. Trichlorofluoromethane has ...
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  • 1,482
8 votes

Experiment to prove that water has air

There are two ways that I interpret the question you're asking, and I'll try to address each in turn. If your teacher boiled a container of water and held a piece of glass above it to collect drops ...
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8 votes
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Why does tetrachloromethane have a higher boiling point than trichloromethane?

You also need to account for the difference in dispersion forces between the two molecules. Chlorine is much larger than hydrogen. Therefore tetrachloromethane has a larger molecular surface area ...
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  • 492
8 votes

Why do the melting and boiling points of the noble gases increase when the atomic number increases?

Other answers have mentioned that dispersion forces are the key to answering the question but not how they increase from helium to radon (or let’s take xenon because that’s not radioactive so I feel ...
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