Salt+Melting+Ice+Explained

Salt melts ice essentially because adding salt lowers the freezing point of the water. How does lower the freezing point melt ice? Well, it doesn't, unless there is a little water on the ice. Fortunately, ice typically is coated with a thin film of liquid water, which is all it takes.

The water molecules are held together in ice by intermolecular attraction. When ice turns to water, the molecules have gained enough kinetic energy to break free from other molecules. When water molecules freeze, the molecules loose enough kinetic energy intermolecular attraction sticks them together.

In pure-water ice, water molecule break free from the ice and move into this film of water, but other water molecules in the water stick to the ice. Salt will dissolve in this thin film of water adding particles to the water. These salt particles block the water that would normally stick back to the ice. With this blocking, the ice can only exist at a lower temperature when the water molecules have even less kinetic energy.

https://www. thoughtco.com/why-does-salt-melt-ice-607896

................................................. We throw salt on the ground to prevent ice from forming. Ice does not form because salt lowers the freezing temperature of water. But how does it do this? When the temperature lowers, molecules in pure water slow down. Eventually. the molecules move so slowly that they can no longer escape the intermolecular attractions between water molecules. As a result of these forces, a lattice of water molecules form and water becomes ice.

During this phase change, water molecules enter and leave the solid at the same rate. Salt disrupts this equilibrium by simply being present. With the addition of salt, less water molecules are present at the interface between liquid and solid. In other words, salt particles block the water molecules from re-entering the solid phase, so more water molecules are leaving and less are entering the solid. When the temperature lowers even further, the water molecules leaving the solid phase will slow down even further and the rate will eventually match the rate at which water molecules can find the solid in the presence of salt. When the rate at which water leaves the solid balances the rate at which water molecules enter, a new (lower) freezing point is established.

http:// blog.science-matters.org/2011/09/26/chemistry-the-effect-of-salt-on-the-freezing-point-of-water/

......................................................... Why is there a thin layer of water on ice? https://phys.org/news/2016-11-longstanding-questionwhy-surface-ice.html ............................................................. Melting Below Zero http://www.phy.ohiou.edu/~elster/pdf/IceS.pdf