Why Does a Mixture of Antifreeze & Water Freeze at Lower Temperatures?

Antifreeze, also known as coolant, is usually a mixture of water and a chemical known as ethylene glycol. Coolant is part of a vehicle's cooling system, and its chemical properties help prevent overheating and decrease freezing temperatures. The effect of mixing antifreeze and water to change the temperatures at which molecular transformations occur is simple chemistry.

Freezing Points

Pure ethylene glycol and pure water individually freeze at the same temperature, 32 F. A 50/50 mixture of each changes the freezing temperature to 34 F. Combinations other than the standard 50/50 will have different freezing and boiling points.

Freezing Point Depression

This chemical effect, known as freezing point depression, is part of a larger phenomenon called colligative properties.

Colligative Properties

Impurities (solutes) are added to a pure substance (the solvent), affecting the properties at which certain pressure changes occur. Adding the solute theoretically stabilizes the solvent and therefore decreases freezing temperature while increasing boiling temperature.