Freezing-point depression describes the phenomenon that the freezing point of a liquid (a solvent) is depressed when another compound is added, meaning that a solution has a lower freezing point than a pure solvent. The melting point of a solid is the temperature range at which it changes state from solid to Liquid. Liquid is one of the principal States of matter. A liquid is a Fluid that has the particles loose and can freely form a distinct surface at the boundaries of A solvent is a liquid or gas that dissolves a solid liquid or gaseous Solute, resulting in a Solution. In Chemistry, a solution is a Homogeneous Mixture composed of two or more substances A solvent is a liquid or gas that dissolves a solid liquid or gaseous Solute, resulting in a Solution. This happens whenever a solute is added to a pure solvent, such as water. The phenomenon may be observed in sea water, which due to its salt content remains liquid at temperatures below 0°C, the freezing point of pure water. Seawater is Water from a Sea or Ocean. On average seawater in the world's oceans has a Salinity of about 3

Explanation

The change in chemical potential of a solvent when a solute is added explains why freezing point depression takes place.

The freezing point depression is a colligative property, which means that it is dependent on the presence of dissolved particles and their number, but not their identity. Colligative properties are properties of solutions that depend on the number of particles in a given volume of solvent and not on the mass of the particles It is an effect of the dilution of the solvent in the presence of a solute. It is a phenomenon that happens for all solutes in all solutions, even in ideal solutions, and does not depend on any specific solute-solvent interactions. (Explanations claiming that the solute molecules somehow "prevent" the solvent molecules from forming a solid are thus wrong. ) The freezing point depression happens both when the solute is an electrolyte, such as various salts, and a nonelectrolyte. An electrolyte is any substance containing free Ions that behaves as an electrically conductive medium In thermodynamic terms, the origin of the freezing point depression is entropic and is most easily explained in terms of the chemical potential of the solvent. In Physics, thermodynamics (from the Greek θερμη therme meaning " Heat " and δυναμις dynamis meaning " In Thermodynamics (a branch of Physics) entropy, symbolized by S, is a measure of the unavailability of a system ’s Energy In Thermodynamics and Chemistry, chemical potential, symbolized by μ, is a term introduced by the American engineer chemist and mathematical

At the freezing (or melting) point, the solid phase and the liquid phase have the same chemical potential meaning that they are energetically equivalent. The chemical potential is dependent on the temperature, and at other temperatures either the solid or the liquid phase has a lower chemical potential and is more energetically favourable than the other phase. In many cases, a solute does only dissolve in the liquid solvent and not in the solid solvent. This means that when such a solute is added, the chemical potential of the solvent in the liquid phase is decreased by dilution, but the chemical potential of the solvent in the solid phase is not affected. This means in turn that the equilibrium between the solid and liquid phase is established at another temperature for a solution than a pure liquid; i. e. , the freezing point is depressed. ^[1]

The phenomenon of boiling point elevation is analogous to freezing point depression. Boiling-point elevation describes the phenomenon that the Boiling point of a Liquid (a Solvent) will be higher when another compound is added meaning that However, the magnitude of the freezing point depression is larger than the boiling point elevation for the same solvent and the same concentration of a solute. Because of these two phenomena, the liquid range of a solvent is increased in the presence of a solute.

Calculations

The extent of freezing-point depression can be calculated by applying Clausius-Clapeyron relation and Raoult's law together with the assumption of the non-solubility of the solute in the solid solvent. The Clausius-Clapeyron relation, named after Rudolf Clausius and Émile Clapeyron, is a way of characterizing the Phase transition between two phases of Established by François-Marie Raoult, Raoult's law states the Vapor pressure of an Ideal solution is dependent on the vapor pressure of each The result is that in dilute ideal solutions, the extent of freezing-point depression is directly proportional to the molal concentration of the solution according to the equation^[1]

ΔT_f = K_f · m_B

where

• ΔT_f, the freezing point depression, is defined as T_{f (pure solvent)} − T_{f (solution)}, the difference between the freezing point of the pure solvent and the solution. In Chemistry, concentration is the measure of how much of a given substance there is mixed with another substance It is defined to assume positive values when the freezing point depression takes place.
• K_f, the cryoscopic constant, which is dependent on the properties of the solvent. In thermodynamics the cryoscopic constant, Kf allows one to relate Molality to Freezing point depression. It can be calculated as K_f = RT_m²M/ΔH_f, where R is the gas constant, T_m is the melting point of the pure solvent in kelvin, M is the molar mass of the solvent, and ΔH_f is the heat of fusion per mole of the solvent. Relationship with the Boltzmann constant The Boltzmann constant kB (often abbreviated k) may be used in place of the gas constant by working The melting point of a solid is the temperature range at which it changes state from solid to Liquid. The standard Enthalpy of fusion (symbol \Delta{}H_{fus} also known as the heat of fusion or specific melting heat, is the amount of
• m_B is the molality of the solution, calculated by taking dissociation into account since the freezing point depression is a colligative property, dependent on the number of particles in solution. In Chemistry, concentration is the measure of how much of a given substance there is mixed with another substance Dissociation in Chemistry and Biochemistry is a general process in which ionic compounds ( complexes, Molecules, or Salts) separate This is most easily done by using the van 't Hoff factor i as m_B = m_solute · i. In Physical chemistry, the van 't Hoff factor i is the number of moles of Solute actually in Solution per mole of solid solute added The factor i accounts for the number of individual particles (typically ions) formed by a compound in solution. Examples:
  • i = 1 for sugar in water
  • i = 2 for sodium chloride in water, due to dissociation of NaCl into Na⁺ and Cl^-
  • i = 3 for calcium chloride in water, due to dissociation of CaCl₂ into Ca²⁺ and 2 Cl^-
  • i = 2 for hydrogen chloride in water, due to complete dissociation of HCl into H⁺ and Cl^-
  • i = 1 for hydrogen chloride in benzene, due to no dissociation of HCl in a non-polar solvent

At high concentrations, the above formula is less precise due to the approximations used in its derivation and any nonideality of the solution. Solubility of Pure SucroseTemperature(Cg For sodium chloride in the diet see Salt. Sodium chloride, also known as common salt, table salt, or Halite, is a Calcium chloride (CaCl2 is an ionic compound of Calcium and Chlorine. In Chemistry, an ideal solution or ideal mixture is a Solution in which the Enthalpy of solution is zero the closer to zero the enthalpy of If the solute is highly soluble in the solid solvent, one of the key assumptions used in deriving the formula is not true. In this case the effect of the solute on the freezing point must be determined from the phase diagram of the mixture. In Physical chemistry, Mineralogy, and Materials science, a phase diagram is a type of graph used to show the equilibrium conditions

Cryoscopic constants

Values of the cryoscopic constant K_f for selected solvents:^[2][3]

Uses

The phenomenon of freezing point depression is used in technical applications to avoid freezing. In the case of water, ethylene glycol or other forms of antifreeze is added to cooling water in internal combustion engines, making the water stay a liquid at temperatures below its normal freezing point. Ethylene glycol ( monoethylene glycol ( MEG) 12-ethanediol, IUPAC name: ethane-12-diol) is an Alcohol with two -OH Antifreeze is a Cryoprotectant used in Internal combustion engines and for many other heat transfer applications such as electronics cooling and Chillers The internal combustion engine is an engine in which the Combustion of Fuel and an Oxidizer (typically air occurs in a confined space called a

The use of freezing-point depression through "freeze avoidance" has also evolved in some animals that live in very cold environments. eVolution is the third Album by eLDee, it was due to be released in 2008 This happens through permanently high concentration of physiologically rather inert substances such as sorbitol or glycerol to increase the molality of fluids in cells and tissues, and thus decrease the freezing point. Physiology (from Greek grc φύσις physis, "nature origin" and grc -λογία -logia) is the study of the mechanical physical Sorbitol, also known as glucitol, is a Sugar alcohol that the body metabolises slowly Examples include some species of arctic-living fish, such as rainbow smelt, which need to be able to survive in freezing temperatures for a long time. The Arctic is the Region around the Earth 's North Pole, opposite the Antarctic region around the South Pole. Fish are aquatic Vertebrate animals that are typically ectothermic (previously Cold-blooded) covered with scales, and equipped with two Rainbow Smelt ( Osmerus mordax) is an Anadromous Species of Fish inhabiting rivers and coastal areas of North America from In other animals, such as the peeper frog (Pseudacris crucifer), the molality is increased temporarily as a reaction to cold temperatures. A spring peeper ( Pseudacris crucifer) is a small Tree frog widespread throughout the eastern USA and Canada. In the case of the peeper frog, this happens by massive breakdown of glycogen in the frog's liver and subsequent release of massive amounts of glucose. Glycogen is a Polysaccharide of Glucose (Glc which functions as the secondary short term energy storage in Animal cells Glucose (Glc a Monosaccharide (or simple Sugar) also known as grape sugar, is an important Carbohydrate in Biology. ^[4]

Together with formula above, freezing-point depression can be used to measure the degree of dissociation or the molar mass of the solute. Dissociation in Chemistry and Biochemistry is a general process in which ionic compounds ( complexes, Molecules, or Salts) separate Molar mass, symbol M, is the Mass of one mole of a substance ( Chemical element or Chemical compound) This kind of measurement is called cryoscopy (Greek "chillawatchsts") and relies on exact measurement of the freezing point. The Ancient Greek language is the historical stage in the development of the Hellenic language family spanning the Archaic (c The degree of dissociation is measured by determining the van 't Hoff factor i by first determining m_B and then comparing it to m_solute. In this case, the molar mass of the solute must be known. The molar mass of a solute is determined by comparing m_B with the amount of solute dissolved. In this case, i must be known, and the procedure is primarily useful for organic compounds using a nonpolar solvent. Cryoscopy is no longer as common a measurement method as it once was. As an example, it was still taught as a useful analytic procedure in Cohen's Practical Organic Chemistry of 1910,^[5] in which the molar mass of napthalene is determined in a so-called Beckmann freezing apparatus. Molar mass, symbol M, is the Mass of one mole of a substance ( Chemical element or Chemical compound) Naphthalene, also known as naphthalin, naphthaline, tar camphor, white tar, albocarbon, or antimite and not to be

In principle, the boiling point elevation and the freezing point depression could be used interchangeably for this purpose. However, the cryoscopic constant is larger than the ebullioscopic constant and the freezing point is often easier to measure with precision, which means measurements using the freezing point depression are more precise. In thermodynamics the ebullioscopic constant, Kb allows one to relate Molality to Boiling point elevation.

See also

• Boiling-point elevation
• Eutectic point
• Colligative properties
• List of boiling and freezing information of solvents

References