The endothermic reaction by the solid or ice in this case is allowing the ice to melt. The reaction however is causing the solid ice to turn into a liquid form. As the ice in the reaction replaces the heat in the ingredients bag it makes ice cream solidify. When we add the element salt into the reaction it tends to break down and dissociate into two sepraete particles. When this happens it breaks into the two compounds known as Sodium and Chlorine which allows it to lower a freezing point of the ingredients together. This causes the freezing point depressions.

The freezing point depression is also know as the colligative property. The freezing point of something is the temperature which the vapor pressures of the solid and liquid phases are the same. When the solute is nonvolatile the temperature of the substance and the solid phase have the same vapor pressure which is reduced. The mixture of salt and ice is believed to create the lowest temperature that could be reached by humans