4 replies to this topic

[dylant]

Besides HCl, what other liquid has a very low boiling point? (below -150 Celc)

Thanks,
Dylan

[gvdlans]

A very strange post I would say:

HCl (hydrochloric acid) has a boiling point of 230°F (= 110°C), see http://www.bu.edu/es...hloricAcid.html or http://ptcl.chem.ox....loric_acid.html

A substance with a boiling point below -150°C is normally not called a liquid but a gas... There are many substances with a boiling point below -150°C, for example methane (-161°C) or nitrogen (-196°C).

Could you explain why you posted this question?

[MrShorty]

+110C would be the boiling point for an aqueous solution of HCl. The boiling point referred to by the OP is probably for anhydrous HCl, though DIPPR claims that HCl has a normal boiling point of ~188 K (~-85 C) and a melting point of ~155 K (~-120 C), so I wouldn't say that it has a boiling point below -150 C. Technically, we can still talk about solid HCl in equilibrium with its vapor, but one normally wouldn't call that a "boiling point."

As for the original question, what has boiling point (assume 1 atm pressure) below -150 C (120 K). There are several. Methane and nitrogen have been mentioned. Off the top of my head, I also think of oxygen, hydrogen, helium, and argon. I'm not sure, but there might be a good electronic database out there (like DIPPR or NIST) that will allow you to search on boiling point.

[dylant]

Technically, we can still talk about solid HCl in equilibrium with its vapor, but one normally wouldn't call that a "boiling point." >>>> This is what I meant. What do you call when HCl is in equilibrium with the vapor?

I did not intend to say liquid. It's supposed to be fluid.

-Dylan

[MrShorty]

It appears that we need to discuss a little terminology here.

In your original post, you were using the term "boiling point" rather carelessly. When used without qualification, one normally assumes that you mean, "the boiling point at P=1 atm." This is sometimes referred to as the normal boiling point. When you want to refer to something other than the normal boiling point, one should qualify "boiling point" with the pressure of interest.

When a solid turns directly into a vapor, this is usually referred to as "sublimation." Thermodynamically, there is no difference between solid-vapor transitions and vapor-liquid transitions. The Clapeyron equation still holds true, and many of the equations based on the Clapeyron equation (such as the Antoine equation) are used to describe sublimation curves. The hardest part of describing sublimation is that most compounds have very low vapor pressures as solids, and there isn't a lot of data out there measuring vapor pressures of solids. When they could find data, DIPPR's database includes vapor pressure curves for solids.