In a hot summer day the ice-cream street vendor was making ice-cream, right in the street in a steel pot without a freezer or use of electricity. How could he produce such a cold environment to freeze milk and make ice-cream under the hot sun using some crushed ice? Knowing how chemicals can modify freezing point or boiling point of liquids, can help us control the conditions or produce products that otherwise we would not be able to do produce. 

We also use such knowledge to make anti-freeze and prevent freezing at very low temperatures or use chemicals to melt ice.