Question

why do we put rock salt on the roads in winter/fall? it has nothing to do with melting

Answer 1

boiling point

Answer 2

rock salt lowers the temperature of ice to freeze.. so it lowers the freezing point

Answer 3

thank you !!!!!!!!

Answer 4

Although the hydration process gives off heat, this is more than compensated for by the heat absorbed during the initial decomposition of the salt into ions. In other words, the total process of dissolution--decomposition into ions plus hydration--absorbs heat. This can easily be demonstrated: pour some water into a glass and test its temperature with your finger. Add some salt, stir, and test it again. The temperature will have decreased.

The actual reason that the application of salt causes ice to melt is that a solution of water and dissolved salt has a lower freezing point than pure water. When added to ice, salt first dissolves in the film of liquid water that is always present on the surface,thereby lowering its freezing point below the icetemperature. Ice in contact with salty water therefore melts, creating more liquid water, which dissolves more salt, thereby causing more ice to melt, and so on. The higher the concentration of dissolved salt, the lower its overall freezing point. There is a limit, however, to the amount of salt that can be dissolved in water. Water containing a maximum amount of dissolved salt has a freezing point of about zero degrees Fahrenheit. Therefore, the application of salt will not melt the ice on a sidewalk if the temperature is below zero degrees F.

To understand why water containing dissolved salt has a lower freezing point than pure water, consider that when ice and water are in contact there is a dynamic exchange at the interface of the two phase states. Because of thermal vibrations in the ice, a large number of molecules per second become detached from its surface and enter into the water. During the same period of time, a large number of water molecules attach themselves to the surface of the ice and become part of the solid phase. At higher temperatures, the former rate is faster than the latter and the ice melts. At lower temperatures the reverse is true. At the freezing point the two rates are equal. If salt is dissolved in the water, the rate of detachment of the ice molecules is unaffected but the rate at which water molecules attach to the ice surface is decreased, mainly because the concentration of water molecules in the liquid (molecules per cubic centimeter) is lower. Hence, the melting point is lower.

Answer 5

lowers the temp :)