Questions tagged [boiling-point]

The boiling point of a substance is the temperature at which the vapor pressure of the liquid equals the environmental pressure surrounding the liquid

Filter by
Sorted by
Tagged with
23
votes
3answers
24k views

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

As pointed out in the comments to this question, cyclic hydrocarbons have higher boiling points than their acyclic isomers. The major attractive force for hydrocarbons should be the London forces, ...
23
votes
2answers
71k views

Why do different substances have different boiling points?

For example, why does for example oxygen turn into gas at a much lower temperature than water? Does it have anything to do with the molecular structure? A water molecule does have a more complex ...
22
votes
2answers
3k views

Why do alkanes have higher boiling point than their ether counterparts?

Based on my understanding of inter-molecular forces, I expect dipole-dipole interactions to be significantly stronger than van der Waal's interactions. Hence, I expect ethers (which obviously have ...
20
votes
4answers
3k views

Will gaseous ionic compounds be free moving ions?

I knew while learning about electrolysis that if the ionic compound is molten it becomes free moving ions. If that is the case, what will happen if I continued heating till it reaches the boiling ...
19
votes
2answers
4k views

Why is the boiling point of stibane higher than that of ammonia?

I recently came across the fact that the boiling point of $\ce{SbH3}$ (stibane) is greater than that of $\ce{NH3}$ (ammonia). I was expecting $\ce{NH3}$ to have a greater boiling point as a ...
17
votes
5answers
7k views

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

Which substances exist that are normally liquid and that will not freeze nor boil even at relatively low/high temperatures as compared to the freezing and boiling points of water? Or how can I ...
16
votes
4answers
88k views

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

What causes the melting and boiling points of noble gases to rise when the atomic number increases? What role do the valence electrons play in this?
16
votes
3answers
987 views

Why doesn't the boiling point of an aqueous solution depend on intermolecular attraction?

I understand that boiling point is a colligative property for aqueous solutions, and that it empirically depends on the mole fraction of the solute, rather than the identity of the solute. I ...
14
votes
0answers
10k views

Melting and boiling point trend in Group II

The following picture shows the melting and boiling point trends down group II elements. I have added question marks where the variability in data was rather disturbing (over two hundred degrees ...
13
votes
1answer
4k views

Why does silicon tetrafluoride have a higher melting point than sulfur tetrafluoride?

So looking at the Wikipedia pages of sulfur tetrafluoride and silicon tetrafluoride, the melting points are −121 °C and −90 °C respectively, and so $\ce{SiF4}$ has the higher melting point. However, ...
12
votes
2answers
5k views

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

I was wondering if the following justification for freezing point depression and boiling point elevation are conceptually correct. The reason why I ask this question is because I have been self ...
12
votes
3answers
52k views

Why are the boiling points of aldehydes less than those of ketones?

Both aldehydes and ketones have a carbonyl group, but since the carbonyl group of ketone is between alkyl groups, wouldn't it be more difficult for it to form hydrogen bonds than aldehydes? Why then, ...
12
votes
1answer
1k views

Confusion over boiling point of gallium

I am completing a project on gallium, and I need to include its boiling point. I thought that this would be fairly simple to look up, however, it appears that different sources quote different ...
10
votes
1answer
50k views

Boiling and melting point of trans- and cis-but-2-ene

The boiling point of trans-but-2-ene is lower than that of its cis isomer but the melting point of the former is higher than the later. Why is it not following the same order? Is there any factor of ...
10
votes
2answers
58k views

Arrange these compounds: CO2, CH3OH, RbF, CH3Br in order of increasing boiling points

Arrange these compounds: $\ce{CO2}$, $\ce{CH3OH}$, $\ce{RbF}$, $\ce{CH3Br}$ in order of increasing boiling points. I think I should consider the forces between them, that is: $\ce{CO2}$: dispersion ...
9
votes
1answer
85k views

Alkane, alkene, alkyne boiling point comparison

Which of the following has higher boiling points? Alkanes, alkenes, or alkynes? And why?
9
votes
2answers
683 views

400–430 degrees Celsius heated bath

I want to perform a reaction which needs the temperature to be maintained between 400–430 °C. Since it's the only practical solution, I opted for a heated bath. I'm looking for a hydrocarbon fraction/...
9
votes
2answers
2k views

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

TL;DR version is the question title. Some context and data follow. I was creating an assignment for my organic chemistry students in which they would need to draw as many isomers as they could from a ...
9
votes
1answer
1k views

How is it possible for a substance to have a high heat of vaporization but a low boiling point?

The final paragraph of Dissenter's question here is worthy of standing alone: [H]ow does one square a high heat of vaporization with a low boiling point? If it takes a lot of energy to vaporize ...
8
votes
2answers
1k views

Enrichment of D2O

The Wikipedia page for deuterium oxide (heavy water) says that its boiling point is 374.5 K and the one for ordinary water is 373.13 K. Is there a way of distillation which we can use to enrich ...
8
votes
3answers
8k views

Experiment to prove that water has air

In elementary school, there was an experiment to show that water has dissolved air, which involved boiling some water and observing the drops at the surface of the container, and this proved that ...
8
votes
4answers
8k views

Reason for the formation of azeotropes

Why is it that some liquid mixtures (that exhibit positive/negative deviation from Raoult's law) form azeotropic mixtures at certain compositions? What is the physical reason behind this; are there ...
8
votes
1answer
676 views

Boiling point of alkynes from n = 2 to 10

From a video on organic chemistry, I found this table that shows the boiling point temperatures of alkynes $\ce{C_{n}H_{2n-2}}$ with $\,n=2...10$. $$\begin{array}{|c|c|c|c|} \hline n & t_\mathrm{...
8
votes
2answers
160 views

Is it true that an evaporating molecule has the same kinetic energy as a molecule in a pot of boiling water?

A molecule on the surface of room-temperature water shoots off the surface of said water, or in other words, it "evaporates." It does so because it gained kinetic energy ${x}$, and ${x}$ was great ...
8
votes
1answer
855 views

What determines humidity limit / dew point of the air? - Why can air only hold a certain amount of water?

From Wikipedia: The dew point is the temperature at which the water vapor in a sample of air at constant barometric pressure condenses into liquid water at the same rate at which it evaporates. At ...
8
votes
4answers
5k views

Why is the boiling point of m-dichlorobenzene less than that of p-dichlorobenzene?

Why is the boiling point of m-dichlorobenzene less than that of p-dichlorobenzene? Shouldn't the former have a higher boiling point because it possesses a dipole moment? I think the van der Waals ...
8
votes
3answers
4k views

Why is the boiling point of heavy water more than that of normal water?

In class we learnt that the London forces become stronger as the relative molecular mass increases. Not just as in organic chemistry but in things like the halogens. However, as I understand, the ...
7
votes
3answers
2k views

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?

I've seen some formulas around in other questions and Google searches, but my chemistry is pretty much dead so I have no clue where to find the relevant values to calculate it myself. I just need to ...
7
votes
1answer
16k views

Caffeine boiling and melting points

According to both caffeine's pubchem page and chemspider page its boiling point lies at 173°C and its melting point at ~235°C. How can it melt at that temperature if it already sublimated at 173°C? Or ...
7
votes
2answers
6k views

Why does decreasing the pressure of the system increase the relative volatility of a binary solution?

In our teaching lab, we were posed with the following question as an exersize: If the boiling points of two compounds differ by $\pu{50 ^\circ C}$ at atmospheric pressure, what will be the effect ...
7
votes
2answers
9k views

Why does tetrachloromethane have a higher boiling point than trichloromethane?

London dispersion forces (LDF) are present in all molecules, whether polar or non-polar. Molecules also exhibiting dipole-dipole interactions (in addition to the LDF) must have stronger forces of ...
7
votes
2answers
2k views

How are the boiling points of Tungsten and other metals determined and proved?

The boiling point of Tungsten is 10,030 degrees Fahrenheit. How was this determined and proved? And more generally how are the boiling points of metals determined and proved? Is it really so simple ...
7
votes
1answer
550 views

Why does acetonitrile have a larger dipole moment and boiling point than acetaldehyde?

Experimentally, acetonitrile has a larger dipole moment than acetaldehyde, but I've never understood why. I always thought that the charge separation between carbon/oxygen is larger than that of ...
7
votes
1answer
705 views

Does the boiling boint of miscible liquids follow a linear relationship?

I want to create a steam bath for a reaction the proceeds well at 105℃. I cannot use pure (demineralized, anyway) water for this, since it would boil at 100℃ at STP. As such I figured ...
7
votes
0answers
271 views

Why do chlorinated silanes have lower boiling points than their methane analogs?

The boiling points of the chlorinated silanes and methanes are given below: $$\begin{array}{ccc} \hline \text{Species} & \text{Boiling point (X = Si) / }\mathrm{^\circ C} & \text{Boiling ...
6
votes
1answer
266 views

IChO problem involving the condensation point of NF3, NHF2, NH2F

This is a problem from the 2016 International Chemistry Olympiad (IChO): Which of $\ce{NF3}$, $\ce{NHF2}$, and $\ce{NH2F}$ condenses at the lowest temperature? The answer book says that it is $\ce{...
6
votes
1answer
255 views

Large difference in boiling points of tetrafluoromethane and tetrachloromethane

Why is carbon tetrachloride $\ce{CCl4}$ is seen to posses liquid state (b.p. $\pu{76.72 °C}),$ whereas carbon tetrafluoride $\ce{CF4}$ is in gaseous state at room temperature (b.p. $\pu{−127.8 °C})?$
6
votes
2answers
9k views

Why is the boiling point of sulfuric acid much higher than that of phosphoric acid?

Why is boiling point of sulfuric acid much higher than that of phosphoric acid? According to the data book, • The boiling point of sulfuric acid is 337 °C (639 °F; 610 K) When sulfuric acid is ...
6
votes
1answer
2k views

Trend in the boiling point of the hydrogen halides

The boiling points of the hydrogen halides are as follows: $$\begin{array}{cc} \hline \text{Species} & \text{Boiling point / }\mathrm{^\circ C} \\ \hline \ce{HCl} & -85.1 \\ \ce{HBr} & -...
6
votes
1answer
6k views

Hydrogen bonding in alcohols vs amines

Consider an alcohol and an amine compound with roughly the same molar mass. If I understand correctly, the boiling point for the alcohol is greater for two reasons: The $\ce{O-H}$ bond is more polar ...
6
votes
1answer
548 views

Why are the dispersion forces in CS2 stronger than the dipole-dipole forces in COS?

London dispersion forces supposedly have the least strength out of all the intermolecular forces. But $\ce{CS2}$, which has only dispersion forces, has a higher boiling point (and thus stronger ...
6
votes
1answer
93 views

What are the physical properties affected in ZnO when there is a sulfur impurity?

I have a question. I work at a brass metal foundry where one of our waste products is $\ce{ZnO}$, which we sell. Because we have been making new alloys which contain sulfur, our $\ce{ZnO}$ has a very ...
6
votes
2answers
396 views

Real boiling temperature

I've been thaught that water at 1 atm water boils at 100 °C (the so called “normal boiling point”). However, I came across a more rigorous description of the boiling process saying that in order to ...
5
votes
2answers
4k views

Does more branching lead to lower boiling point in alkanes?

List the following alkanes in order of increasing boiling point. A. $\ce{CH3(CH2)4CH3}$ B. $\ce{(CH3)2CHCH(CH3)2}$ C. $\ce{CH3CH2CH(CH3)CH2CH3}$ Answer: $C<B<A$, low to high. ...
5
votes
2answers
611 views

Why do alkenes with more surface contact have greater London forces?

Why is it that alkenes with greater surface contact have greater London forces? I thought greater London forces were dependent on the size of the molecules, or the number of electrons, rather than the ...
5
votes
1answer
4k views

Boiling point trend in group 13

My Theory: Since atomic mass increases down the group, the van der Waal's forces should also operate to a greater extent, thereby making it difficult to change the phase of the substance. Hence, ...
5
votes
1answer
201 views

Throwing water into lava

While discussing magma in class with my students, I showed a video of a man throwing water onto molten, running lava. A large flame ensued. I realize that the water is being converted into steam and ...
5
votes
4answers
1k views

Does a freezing point of a substance always increase as its boiling point increases?

I am studying for an introductory to physical sciences test and came upon a chart describing substances found in petroleum and the distillation process. Each freezing point increases as each boiling ...
4
votes
1answer
2k views

Boil to dry 50 liters water

I would like to find out how long it would take to completely turn 50 litres of water to steam. Let's assume power of 2500 W and the water is already at boil. I am not very scientific so please ...
4
votes
2answers
2k views

Elevated boiling points in alkanes with even number of carbons [duplicate]

Why do alkanes with even number of carbon atoms have greater boiling points than those with odd number of carbon atoms?