Why salt causes ice to melt?

We all have heard about the use of salt in the deicing of roads. When we add salt to ice, the ice melts. Let us learn what is the chemistry behind this phenomenon.

Ice is not a complete solid at 0 degrees Celsius rather it is a mixture of liquid water and solid water in dynamic equilibrium with each other, having the same vapor pressure.

The addition of salt causes the vapor pressure of the liquid to decrease. This decrease arises due to the dissolution of salt in water. The dissolution makes lesser water molecules available for evaporation so the vapor pressure decreases.

As the vapor pressure is lower so the liquid water will loss greater energy (attain temperature lower than 0 degrees Celsius) to reach to the vapor pressure of solid water. This is the reason why ice melts when you add salt to it.

But, the addition of salt does not always cause the ice to melt rather it can also be used for freezing. How is salt used to make the freezing mixture??? We will discuss this in our next article.