How does salt help to make ice and snow melt?
Salt reduces the freezing point of water by reducing the partial pressure of water. When you have a salt solution, the ions shift the vapor-pressure equilibrium of water. Salt does this because salt does not have a vapor pressure. So when salt ions share space with water by being in a solution, there are fewer water molecules per volume. This reduces the vapor or partial pressure of water. Once the water has a lower vapor pressure, it takes a lower temperature to slow down the water molecules enough to form a solid. So it has a lower freezing point. That’s why the ice/snow melts at the previously freezing but now melting temperature. The temperature has not changed. The melting point did.