Question

Using the phase diagram for water and Raoult’s law, explain why salt is spread on the roads in winter (even when the temperature is below freezing).

Short answer

It lowers the melting point of the water.

Step-by-step solution

concept

If we add the salt on the top of ice, it dissolves in a thin layer of liquid water, which is always present on the top.

The solution of salt in the thin layer of liquid water has a lower melting point than pure water.

Ice in contact with the salty water then melts, create more salty water.

Step 2:Explain the reasoning

Using thephase diagram for waterif we move the melting point to the left, the state with the lowest energy on is then the liquid state.

Using the Raoult’s lawif we add a non-volatile solute, the mixture will have a lower boiling point than the pure solvent.