Earth Science - Other

Why does Salt Melt Snow and Ice

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"Why does Salt Melt Snow and Ice"
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Snow and ice can be either a winter wonderland or a horrible weather hazard.  Snow is great for making snowballs.  It is wonderful for constructing frolicy snowmen. Ice is awesome for ice-skating and icicles.  Snow and ice can be part of great fun and games for some people.   It has been for ages.  Even with the anticipation of a "winter wonderland," care must be used in dealing with snow and ice.  What about the snow and ice on porches, walkways, and driveways?  This doesn't give much of a "wonderland" feeling.  What about driving on icy roads?  This doesn't either.  These are all hazards that come with the territory of winter.  The best way in dealing with snow and ice is salt, and alot of it.  Why does salt melt snow and ice? 

In general, salt lowers the freezing point of snow and ice.  Water generally freezes at 32 degrees.  Salt lowers this.  It then slows the phase change.  This affects the phase equilibrium.  Once the point is reached where water freezes at the same rate it thaws, dynamic equilibrium is reached.  Unless something changes they will remain in this dynamic equilibrium state.

Not all forms of salt work the same for melting snow and ice.  Different forms of salt include:  sodium chloride,calcium chloride,potassium chloride, and magnesium chloride.  Calcium chloride works at lower temperatures than the others.  This is the type salt used least on roads in "salt trucks."  It is more expensive than other salts. Sodium chloride(commonly known as table salt) doesn't work in as low of temperatures.  It's only good above 15 degrees or so.  However, it is used most often in salt trucks.  However, if table salt is all you have, it will certainly help slick porch and steps.  Magnesium Chloride is generally a liquid "pre-wetting" treatment for roads.  It releases heat to melt snow and ice.  Potassium chloride doesn't melt as well as the others.  For the home salt consumer, buy it in bulk for driveways, walkways, steps, and porches.  It can be more expensive in smaller amounts.

Whether you look forward to the snow and ice, or you dread the very thought of it, be careful.  Be especially careful if you are out there on the snow and ice other than for fun.  Have fun with the snowballs and snowmen when possible.  Rest assured chemists have worked hard to devise the perfect combination of road salts to keep roadways clear. As for driveways, one may have to resort to the good old fashioned shovel before even fathoming the thought of melting salts.  It is good to have fun in the winter, however precautions must be taken to keep everyone safe as well.  Stock up on salt for home too, just as an extra added precaution. It is better to have too much than too little, just to be on the safe side.

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