Understanding the Melting Process with Salt

To illustrate this concept, let's conduct a simple experiment. Begin by collecting half a glass of snow and spreading another handful on a board. Allow the snow on the board to melt naturally. When you place a glass on the resulting water and measure the temperature inside it, you'll find it close to 0°C.

Next, add a small amount of salt into the glass, stir it, and immediately take the temperature again. Surprisingly, the thermometer will show around -18°C. Over time, the temperature will gradually start to rise, but the bottom of the glass may freeze to the board. Why does this occur?

The addition of salt to the glass causes a significant drop in the melting point of ice, possibly to around -21°C. The process of melting ice demands a considerable amount of energy, which is absorbed from the environment and the mixture. In this scenario, the water puddle on the board freezes rapidly, resulting in the temperature decrease of the snow-salt mixture. This mechanism is effectively utilized during icy conditions, where salt is often spread on icy surfaces. This forms a specific layer that leads to the melting of snow and ice as the freezing point of this layer decreases.

As the process continues, a film of water-salt solution emerges, expanding and enlarging to enhance the contact between the ice and salt. This procedure continues until all the ice is melted. The energy required for this reaction is extracted from the surrounding air, causing the area with the snow-salt slurry to feel colder.

Taking a deeper look at the process, when ice is topped with a thin layer of quasi-liquid water, it's created by the fastest moving molecules that detach from the ice crystal. At temperatures below zero, these molecules swiftly reattach to the crystal.

By dissolving in this quasi-liquid layer, salt minimizes the concentration of molecules, slowing down their return from a liquid to solid state, causing the ice to melt. Nonetheless, in extremely low temperatures, salt alone may not suffice to melt the ice completely.