Why are sidewalks salted during winter?

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Offline 00

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Why are sidewalks salted during winter?
« on: 06/02/2011 23:30:02 »
   
Hi, why is salt put on sidewalks with snow during the winter months?



« Last Edit: 28/09/2012 03:10:46 by AH »

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Offline CliffordK

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Why are sidewalks salted during winter?
« Reply #1 on: 06/02/2011 23:45:59 »
To add Flavor  [:o)]

Salt will depress the freezing point (or melting point) of water.  The more concentrated the salt mixture (up to saturation), the more the freezing point is depressed.

So adding salt to ice turns solid ice to liquid water which then can run off, or evaporate, or otherwise is less slippery than ice.

The question might be why adding solid salt to solid ice actually causes it to melt.  Salt itself is quite hygroscopic (it likes water).  Water itself is never fully solid or liquid, but rather exists in an equilibrium between solid, liquid, and gas phases.  This is why sweat evaporates, or the atmosphere can draw water vapor out of the oceans without the oceans boiling.  Anyway, I assume that salt uses this equilibrium to force more and more ice into the liquid phase.