# Tag Info

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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, mostly based on isomerism notions. However, as most of the A grade exams emphasize on the lighter aliphatic compounds, we can understand each other here. :) It'...

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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 and cycloalkanes: (Source) The cycloalkanes have slightly lower molecular mass than their parent unbranched alkanes with the same number of carbon atoms, yet ...

20

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 interactions. Of course the interactions are important in the sense that they affect the entropy but since we are dealing with thermodynamics here the way you think ...

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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 to the larger size of the antimony atom). Our teacher had actually posed this question to us during my first year of high-school. All of us were incredulous ...

19

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 weak London dispersion forces are present between the atoms of the noble gases in the liquid or the solid state. The van der Waals force increases with the ...

19

High symmetry molecules fit into crystal lattices especially well (higher m.p.), but are volatile for having fewer van der Waals interactions (lower b.p.). $$\begin{array}{lrr} \hline \text{Compound} & \text{m.p.}/\pu{°C} & \text{b.p.}/\pu{°C} \\ \hline \text{pentane} & −130 & 36.1 \\ \text{isopentane} & −160 & 27.2 \\ \text{... 17 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 silanes such as tetradodecyl silane as lubricants that are liquid over very wide temperatures. Addendum: Dowtherm A is a eutectic mixture of biphenyl and diphenyl ... 17 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 distillation to produce heavy water as there are better chemical processes that achieve higher enrichment per stage, for example the Girdler sulphide process. 16 It isn't that good a generalization: always look at the data first. Here is a table of most of the aldehydes and ketones with 6 or fewer carbons (the labels are used in the chart later): Now plot this on a chart: Branches is the number of branches in the carbon chain. Note that while for 3 and 4 carbons the ketones do have higher boiling points, it is ... 16 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 much of it is lost to the surroundings. If we assume that all 2500 W is going into the water, it makes things a lot simpler. If the water is already at the ... 16 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 moment enables electronic interactions which hold molecules together . This shows some general factors of boiling point . Also the below link to the google book ... 15 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 following table for the aqueous solutions of common salts and bases. English transcription; column 1: Compound; columns 2–6: Concentration, g/100 g water — boiling ... 14 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? 13 Your best guess for the boiling point of any version of Coke would be 100 C, the boiling point of water. Diet Coke is mostly water (the flavourings are a very small amount relative to the amount of water). The largest ingredient will be the sweetener but there will be only a fraction of a gram of that. It is unlikely you will notice any deviation from the ... 13 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 molecule undergoes a phase change from liquid to gas (e.g. it boils)$$\Delta G_\mathrm{vap} = \Delta H_\mathrm{vap} - T_\mathrm{vap} \times \Delta S_\mathrm{vap} = ...

12

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 dimer where the four atoms are arranged in a wobbly square (the remaining 27%). Traces of Na${}_2$ and Cl${}_2$ are also observed. I expect that as the ...

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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 baths – one product in the Aldrich catalog is advertised as having a working range of −40 °C to +230 °C.

11

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 fluoride which is a salt. Salts generally have a very high boiling point (> 1000 °C, much higher than molecular structures) because of the ionic (electrostatic) ...

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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 ^1, 1.75~ D ^2} \\ \text{1-butene oxide} & \mathrm{1.89~ D^2} \\ \text{ethyl vinyl ether} & \mathrm{1.26~ D ^2} \\ \text{diethyl ether} & \mathrm{1....

11

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 where might that be? Well, there is no formula or theorem that says liquid hydrogen must boil at 20K, nor is there such a thing for any other element, so this ...

11

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 effects related to a change in temperature which also costs energy or releases energy. When liquid ammonia evaporates to gaseous ammonia, energy is required ...

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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 the following values for gallium, quoting original publication [2]: \begin{align} t_\mathrm{tp} (\ce{Ga}) &= \pu{29.7666 ^\circ C} \\ t_\mathrm{m} (\ce{Ga}) &...

10

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 given quantity of a substance from a liquid into a gas at a given pressure." Written symbolically: $$\Delta H_{\mathrm{vap}} = H_{\mathrm{gas}} - H_{\mathrm{liq}... 9 Anhydrous caffeine occurs in two different polymorphic crystal forms, with a transition between the two forms occurring at \pu{136 °C}. The high temperature form has a melting point of \pu{236 °C}. The vapor pressure of the high temperature solid form is described by the equation:$$\log P[\pu{Pa}] = -\frac{5477}{T[\pu{K}]} + 14.395,\tag{1} and for the ...

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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/Fusible_alloy Some of these have melting points below 0 °C and boiling points as high as you will ever need. Some are pretty expensive, though. Note that in general ...

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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 positive hydrogen atoms and how many lone pairs of electrons each have. A water molecule has two partial positive hydrogen atoms and two lone pairs of ...

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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 a standard boiling point just above standard room temperature. You didn't say anything about pressure in your question. If you don't mind pressures higher than ...

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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 safer breathing it). The larger the mass of a nucleus the more protons are in there, and the more protons in a nucleus the more electrons are around the outside....

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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 of liquid water, he or she may have been trying to show that water doesn't disappear when it boils, that instead it turns to a gas that can move through the air ...

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Yes, I think that is the right answer expected for this question. Three factors to consider. (1) Most importantly there four intermolecular forces which effect BP Ionic bonds > Ion-dipole interactions > H bonding > dipole-dipole interactions > Van der Waals dispersion forces. (2) Increasing the number of carbon atoms (e.g. n-alkanes) increases the BP ...

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