Science, Tech, Math › Science Freezing Point Depression Share Flipboard Email Print Daniel Schönherr / EyeEm / Getty Images Science Chemistry Basics Chemical Laws Molecules Periodic Table Projects & Experiments Scientific Method Biochemistry Physical Chemistry Medical Chemistry Chemistry In Everyday Life Famous Chemists Activities for Kids Abbreviations & Acronyms Biology Physics Geology Astronomy Weather & Climate By Anne Marie Helmenstine, Ph.D. Chemistry Expert Ph.D., Biomedical Sciences, University of Tennessee at Knoxville B.A., Physics and Mathematics, Hastings College Dr. Helmenstine holds a Ph.D. in biomedical sciences and is a science writer, educator, and consultant. She has taught science courses at the high school, college, and graduate levels. our editorial process Facebook Facebook Twitter Twitter Anne Marie Helmenstine, Ph.D. Updated July 07, 2019 Freezing point depression occurs when the freezing point of a liquid is lowered or depressed by adding another compound to it. The solution has a lower freezing point than that of the pure solvent. Freezing Point Depression Examples For example, the freezing point of seawater is lower than that of pure water. The freezing point of water to which antifreeze has been added is lower than that of pure water. The freezing point of vodka is lower than that of pure water. Vodka and other high-proof alcoholic beverages typically don't freeze in a home freezer. Yet, the freezing point is higher than that of pure ethanol (-173.5°F or -114.1°C). Vodka may be considered a solution of ethanol (solute) in water (solvent). When considering freezing point depression, look at the freezing point of the solvent. Colligative Properties of Matter Freezing point depression is a colligative property of matter. Colligative properties depend on the number of particles present, not on the type of particles or their mass. So, for example, if both calcium chloride (CaCl2) and sodium chloride (NaCl) completely dissolve in water, the calcium chloride would lower the freezing point more than the sodium chloride because it would produce three particles (one calcium ion and two chloride ions), while the sodium chloride would only produce two particles (one sodium and one chloride ion). Freezing Point Depression Formula Freezing point depression can be calculated using the Clausius-Clapeyron equation and Raoult's law. In a dilute ideal solution, the freezing point is: Freezing Pointtotal = Freezing Pointsolvent - ΔTf where ΔTf = molality * Kf * i Kf = cryoscopic constant (1.86°C kg/mol for the freezing point of water) i = Van't Hoff factor Freezing Point Depression in Everyday Life Freezing point depression has interesting and useful applications. When salt is put on an icy road, the salt mixes with a small amount of liquid water to prevent melting ice from re-freezing. If you mix salt and ice in a bowl or bag, the same process makes the ice colder, which means it can be used for making ice cream. Freezing point depression also explains why vodka doesn't freeze in a freezer.