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Q & A: Gasoline freezing

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Q:
at which temperature does gasoline freeze
- tyler (age 25)
omaha, Ne
A:
Well, gasoline doesn’t really have just one freezing temperature, and in fact, gasoline isn’t made out of just one kind of molecule, but many different hydrocarbons.  If you get it cold enough, it will get pretty hard.  Freezing is a phase change, in which the symmetry of a system reduces -- a liquid with a random distribution of molecules turns into an orderly crystal in a true freezing phase change.  Gasoline on the other hand, just has molecules that slow down as they get colder, and remain in a disordered state at lower temperatures (you might get some crystals of some hydrocarbons if you cool it slowly enough).

Different components have different freezing temperatures.  The alcohols might freeze first, and some of the aromatic hydrocarbons freeze at very low temperatures, below that of dry ice.  The fact that they are all mixed together also depresses the temperatures of onset of solidification.

An example of a common household mixture which doesn’t have much of a freezing temperature is liquid dish soap.  It just gets goopier and eventually hardens up.  I know this from experience, trying to wash dishes in an unheated cabin on a cold, winter morning.  Glass is another example of something which doesn’t truly freeze or melt, although it becomes ductile and even liquid at high temperatures and rigid at low temperatures.

Tom

Often when scientists need a general word for the sorts of frozen , non-crystalline, disordered states that Tom describes we borrow the word ’glass’. Ordinary window glass would then just be one example.  Mike W.

(published on 08/16/06)

Follow-Up #1: Freezing temperatures of different liquids

Q:
Why does gasoline not freeze?
- Anonymous
Albq., N.M.
A:
Get gasoline cold enough and it will freeze.   The actual freezing temperature will depend on subtle properties of its constituents.  Answers vary from -40 to -50 degrees C.

LeeH

(published on 02/22/08)

Follow-up on this answer.