Ask A Scientist© Chemistry Archive

>>
>>    name         Tebbs
>>    status       student
>>    age          16
>>    EMAIL        ATJT@worldnet.att.net
>>    Question -   How is it that an element, like Neon, can have a negative
>> boiling point (Celsius)?  How can you have a boiling point below freezing?

Simple.  Zero Celsius is the freezing point of water, not of everything.
Dimethyl sulfoxide has a freezing point of 18 Celsius, and Ethyl alcohol
has a freezing point of about -114 Celsius.  Neon has a freezing point of
about -249 Celsius, and a boiling point of about -246 Celsius.  So you see,
neon's boiling point is above its freezing point, just as you would expect.

                Richard E. Barrans Jr.
                CHM/200/M019
                Argonne National Laboratory
                9700 South Cass Avenue
                Argonne, IL 60439
                phone: (630) 252-6787
                fax: (630) 252-6862
                e-mail: richb@anl.gov
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Simple.  Zero Celsius is the freezing point of water, not of everything.
Dimethyl sulfoxide has a freezing point of 18 Celsius, and Ethyl alcohol
has a freezing point of about -114 Celsius.  Neon has a freezing point of
about -249 Celsius, and a boiling point of about -246 Celsius.  So you see,
neon's boiling point is above its freezing point, just as you would expect.

                Richard E. Barrans Jr.
                CHM/200/M019
                Argonne National Laboratory
                9700 South Cass Avenue
                Argonne, IL 60439
                phone: (630) 252-6787
                fax: (630) 252-6862
                e-mail: richb@anl.gov

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   Hold on a minute.  What do you boil water in?  A kettle, right?  Why
is it still a liquid when the water is boiling?  How can the steel
have a melting point above the boiling point (100 Celsius)?!
   The answer to this question, as to yours, is that different
substances have different melting and boiling points.  The boiling
point of neon is below the freezing point of water, and the melting
point of steel is above the boiling point of water. 
Grayce
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First, remember that 'freezing' is defined for a specific substance.  That is,
the freezing point of water is 0 deg C, but if you add a little salt or
antifreeze to it, the new solution has a freezing point that is 
negative.  Other
pure substances have different freezing points.  For example, the freezing 
point
of iron is 1535 deg C while the freezing point of hydrogen is -259.14 deg C 
(See
the CRC Handbook of Chmistry and Physics).

Note that one definition of the freezing point of a substance is the 
temperature
at which the liquid and solid phases of the substance exist in 
equilibrium.  You
can pass through this temperature as you cool a substance down and call it the
freezing point or you can heat something up through this temperature and 
call it
the melting point.  The only difference between the two is the direction of the
phase change.

Bradburn
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Dear Tebbs,
Every substance has a different boiling point. Zero degrees
Celsius is the temp where WATER freezes, but many other substances
freeze at higher temps, and lower temps. A few substances,
like helium, don't freeze at all! Rather, they become a superfluid,
an exotic kind of state where liquids have no viscocity.

A good rule of thumb is: the weaker the forces between
two molecules of a liquid are, the lower the melting point will be.

Best wishes,
prof topper
dept of chemistry
the cooper union
new york, ny
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