In science class it was always a safe bet to yell out
"chemical reaction!" since that was usually the answer.
Fortunatelyy for me there are no safe bets in the world of
trivia, otherwise I'd be out of work. What we have here is
more of a physical reaction in which the scheming salt
tricks the ice into self-destruction.

When salt is thrown on an icy pavement, it lands on the
thin layer of water on top of the ice. The water dissolves
some of the salt and makes salt water, which freezes at a
lower temperature than plain water. When the salt
dissolves, it releases a little heat, which melts another
layer of ice, creating another layer of water, which
dissolves more salt, which releases more heat, which makes
more salt water and so on and so on. Eventually you're left
with nothing more than a salty puddle.