Boiling temperature of metals...

[Externet]

Greetings..

Seen on data charts Sb boiling at 1950 C ; Sn boiling at 2602 C  ; Pb boiling at 1749 C ...

If water boils at 100 C, and emits/turns to steam above it; what do metals emit when boiling ?  Themselves in gas form ?   That gas, if cooled, precipitates / 'rains' ?

[TheVat]

37 minutes ago, Externet said:

If water boils at 100 C, and emits/turns to steam above it; what do metals emit when boiling

Vapor.  Boiling means to change phase from liquid to gas.  That is the definition of boiling.  

There are street lights (or were) that rely on the relatively low BP of mercury.  An electric arc is sent through mercury vapor.  USA banned them in 2008.  

[Sensei]

47 minutes ago, Externet said:

Seen on data charts Sb boiling at 1950 C ;

You read incorrectly.

It was 1908 K, which is 1635 C for Sb. Ref https://en.wikipedia.org/wiki/Antimony

The other source says 1587 °C. Ref: https://www.rsc.org/periodic-table/element/51/antimony

 

[studiot]

Just now, Sensei said:

You read incorrectly.

It was 1908 K, which is 1635 C for Sb. Ref https://en.wikipedia.org/wiki/Antimony

The other source says 1587 °C. Ref: https://www.rsc.org/periodic-table/element/51/antimony

 

 

Group V elements (Nitrogen, Phosphorus, Antimony, Arsenic and Bismuth)  have allotropic forms.

The Antimony in particular that exists in its common most stable form at room temperature is called alpha Antimony and has a boiling point of 1587^o C

In addition there are 5 other forms of Sb, two of which are formed at higher pressures and show the higher BP of something over 1600^oC, depending upon the pressure.

So Greenwood and Earnshaw have the alpha form  (Chemistry of the Elemnts)  - 1587^o C

Lange has the types I and II forms - (Handbook of Chemistry)  - 1640^oC

 

Yes metal vapour is given off by the boiling substance.

Antimony also exhibits an unstable form which gives off an explosive gas form.

Edited January 6 by studiot

[Externet]

2 hours ago, TheVat said:

Vapor.  Boiling means to change phase from liquid to gas.  That is the definition of boiling. 

Thank you.  If you leave a glass of water under your bed untouched for a month; it will be then empty as it turned to vapor.   If you heat water to boiling point, turns to steam.  Is that wrong ? 

Isn't vapor the gas under 100C and steam over 100C ?

[TheVat]

Steam is vapor which is visible because some of the vapor is recondensing at it makes contact with cooler ambient air.  So the vapor carries along tiny recondensed droplets of water which give a more visible cloud.   The water in the glass under your bed has a temperature of, say, 20 C, but temperature is just the average kinetic energy of all the molecules, right?  So there are a few molecules that happen to be so energetic that they happen to escape from the glass as vapor.  The average kinetic energy of those escapees is 100 C or more.  Their escape will slightly lower the temp of the glass of water, but only briefly because the water keeps staying in thermal equilibrium with the floor and room air.  

[KJW]

1 hour ago, TheVat said:

The average kinetic energy of those escapees is 100 C or more.

No, the gas is still at 20°C. For example, if one placed a flask containing water at 20°C under a high vacuum, sealing the flask after some of the liquid water had boiled away and all of the air had been removed, then after the temperature of the contents of the flask has been allowed to return to 20°C, both the liquid water in the flask, and the gaseous water above it will be at 20°C. The gaseous water will exert a pressure of 2.3388 kPa (0.0231 atm)¹. And since all the air in the flask has been removed, the entire contents of the flask is water (liquid and gas), and the total pressure inside the flask will be 2.3388 kPa (0.0231 atm). Furthermore, if the flask had not been evacuated, then the partial pressure of the gaseous water molecules (the pressure the water molecules themselves exert within the water-air mixture) would also be 2.3388 kPa (0.0231 atm). That is, the presence of air in the flask does not affect the pressure of the gaseous water molecules in equilibrium with the liquid water at a given temperature.

¹ Source: https://en.wikipedia.org/wiki/Vapour_pressure_of_water
 

[KJW]

I should add that it is the higher kinetic energy water molecules in the liquid phase that escape to the gas phase. But once the higher kinetic energy water molecules in the liquid phase have overcome the potential energy barrier to escape the surface of the liquid, their kinetic energy is reduced to that of the average in the liquid. However, it is not clear to me that the kinetic energy of the water molecules in the liquid phase that escape to the gas phase corresponds to 100°C. 100°C is the boiling point of water at normal atmospheric pressure, whereas the phenomenon described above is independent of the atmospheric pressure.
 

 

[studiot]

Just now, KJW said:

I should add that it is the higher kinetic energy water molecules in the liquid phase that escape to the gas phase. But once the higher kinetic energy water molecules in the liquid phase have overcome the potential energy barrier to escape the surface of the liquid, their kinetic energy is reduced to that of the average in the liquid. However, it is not clear to me that the kinetic energy of the water molecules in the liquid phase that escape to the gas phase corresponds to 100°C. 100°C is the boiling point of water at normal atmospheric pressure, whereas the phenomenon described above is independent of the atmospheric pressure.
 

 

'Boiling point temperature' of any pure liquid depends upon the local atmouspheric pressure.

This is one reason to put lids on saucepans when cooking as the increase in pressure raises the BP a degree or two, leading to more efficient cooking.

At the top of everest it is 68C or 154F for pure water.

Impurities in a liquid also change boiling point.

Thus salt, sugar etc in the saucepan water also raises BP, thought he rise is much less for this mechanism.

[KJW]

6 minutes ago, studiot said:

'Boiling point temperature' of any pure liquid depends upon the local atmospheric pressure.

Yes, that's the point I'm making. But the vapour pressure of a liquid at a given temperature does not depend on the local atmospheric pressure.

 

[studiot]

3 hours ago, Externet said:

Isn't vapor the gas under 100C and steam over 100C ?

The definition of steam is a bit variable.

Engineers talk about wet steam (as with KJW's explanation), which is visible,   and dry steam with no condensate and is invisible.

Physicists and Chemists talk about vapour as a more specific phase or state of a pure substance (water in this case) and may be at any temperature.

Even ice exerts a vapour pressure.

There are also critical points on a phase diagram.

The triple point where solid, liquid and gas (or vapour) can all coexist.

For water this is 0.01 C

 

And the other critical point where the pure substance only exists as a gas or vapour.

 

https://en.wikipedia.org/wiki/Triple_point

 

[KJW]

4 minutes ago, studiot said:

And the other critical point where the pure substance only exists as a gas or vapour.

I prefer to think of the critical point as where the liquid and gas become indistinguishable (the meniscus between them disappears). Interestingly, critical points can only occur between phases that have the same symmetry (e.g. liquid and gas).

 

[exchemist]

1 hour ago, KJW said:

I should add that it is the higher kinetic energy water molecules in the liquid phase that escape to the gas phase. But once the higher kinetic energy water molecules in the liquid phase have overcome the potential energy barrier to escape the surface of the liquid, their kinetic energy is reduced to that of the average in the liquid. However, it is not clear to me that the kinetic energy of the water molecules in the liquid phase that escape to the gas phase corresponds to 100°C. 100°C is the boiling point of water at normal atmospheric pressure, whereas the phenomenon described above is independent of the atmospheric pressure.
 

 

Can one, then, define a sort of “work function” for a molecule to escape the attraction of its neighbours in a condensed phase. I’ve a feeling I should know this but, being in bed with ‘flu’, I can’t think of one.

[John Cuthber]

38 minutes ago, exchemist said:

Can one, then, define a sort of “work function” for a molecule to escape the attraction of its neighbours in a condensed phase. I’ve a feeling I should know this but, being in bed with ‘flu’, I can’t think of one.

Get well soon.
It's the latent heat of evaporation.
 

[exchemist]

3 minutes ago, John Cuthber said:

Get well soon.
It's the latent heat of evaporation.
 

Ah yes, one could express that on a per molecule basis. Thanks. 

[TheVat]

4 hours ago, exchemist said:

Ah yes, one could express that on a per molecule basis. Thanks. 

Thanks to all three of you who weighed in.  I see I was wrong to assume such a high kinetic energy required for an escaping molecule.  I do understand it would quickly be in equilibrium with the ambient air above the meniscus.   And get well, Ex.  (my countrymen sometimes now say "be well," a phrase I'm less fond of)

[exchemist]

1 hour ago, TheVat said:

Thanks to all three of you who weighed in.  I see I was wrong to assume such a high kinetic energy required for an escaping molecule.  I do understand it would quickly be in equilibrium with the ambient air above the meniscus.   And get well, Ex.  (my countrymen sometimes now say "be well," a phrase I'm less fond of)

Thanks, temp down for now at least but sense of taste still screwed up and lungs congested. Might be covid, I suppose, though the cheapo over-the-counter test didn’t come out +ve. When I have more energy I might try to work out the work function, i.e. latent heat, in eV, just for fun.

[exchemist]

22 hours ago, TheVat said:

Vapor.  Boiling means to change phase from liquid to gas.  That is the definition of boiling.  

There are street lights (or were) that rely on the relatively low BP of mercury.  An electric arc is sent through mercury vapor.  USA banned them in 2008.  

In the UK we had sodium vapour lamps for street lighting until only a few years ago, though now almost entirely displaced by LED. One of the curiosities of sodium vapour lamps was because they emit just the sodium D lines, you got false colours. But they were almost universal. I also remember mercury vapour street lights, which also gave false colours. I don’t know offhand what emission lines were excited - green and blue was the general effect.

[swansont]

1 hour ago, exchemist said:

In the UK we had sodium vapour lamps for street lighting until only a few years ago, though now almost entirely displaced by LED. One of the curiosities of sodium vapour lamps was because they emit just the sodium D lines, you got false colours. But they were almost universal. I also remember mercury vapour street lights, which also gave false colours. I don’t know offhand what emission lines were excited - green and blue was the general effect.

Yeah, the Hg spectral lines are in the UV and blue half of the visible spectrum, with nothing in the red, and then IR

184.5 nm, 253.7 nm, 365.4 nm, 404.7 nm, 435.8 nm, 546.1 nm, 578.2 nm and 1014 nm.