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Last updated date: 23rd May 2024
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What is a Parachor?

The Greek words "para" which means "aside" and "chor" which means "space" are thought to have been combined to create the term parachor. S. Sugden suggested the parameter parachor, is related to surface tension, in 1924. Parachor definition can be given by the following equation,

$P\,=\,{{\gamma}^{1/4}}\frac{M}{({{\rho}_{L}}-{{\rho}_{V}})}\,=\,{{\gamma }^{1/4}}V$


$\gamma $ = surface tension

$M$ = molar mass

${{\rho }_{L}}$ = liquid density

${{\rho }_{V}}$ = vapour density in equilibrium with the liquid

Because of the volume multiplier in parachor, it may be extended from components to mixtures hence numerous structure-related problems can be solved with parachor. The conventional units of measurement for the parachor and its group contributions are ${{(erg/c{{m}^{2}})}^{1/4}}\,\times \,(c{{m}^{3}}/mol)$, which is equivalent to ${{(mJ/{{m}^{2}})}^{1/4}}\,\times \,(c{{m}^{3}}/mol)$.

History of Parachor

Sugden demonstrated in earlier articles that every chemical has a distinctive parachor value. Since Sugden's breakthrough, parachor has been employed to "correlate" the surface tension data of a number of different pure liquids and liquid mixtures.

A general molecular theory for parachor that is applicable to all temperature ranges was proposed by Boudh-Hir and Mansoori in 1990.

Escobedo and Mansoori (1996) developed an analytical solution for parachor as a function of temperature that is valid in all temperatures ranging from the melting point to the critical point using the molecular theory of Boudh-Hir and Mansoori.

Additionally, they predicted surface tensions of various liquids in all temperature ranges, from melting point to critical point, using the resultant analytic equation.

Applications of Parachor

The parachor, which is generally constant throughout a large range of temperatures, is defined as the molecular weight of the liquid multiplied by the fourth root of its surface tension divided by the difference between the densities of the liquid and the vapour in equilibrium with it.

It is a molecule's constitutive property that is additive and connected to both surface tension and molar volume. It is an empirical constant for a liquid that connects the surface tension to the molecular volume.

Under conditions where the liquids have similar surface tension, it can be used to estimate molecular volumes and identify incomplete compounds by adding values for the atoms of the ingredients and structural characteristics. Numerous compounds and their structures have been identified using the parachor value. P-benzoquinone, for which the two alternate structures listed below were proposed, is a notable example.

It should be noted that discrepancies in the parachor readings have been found in several instances, including those involving organometallic compounds. Since the development of spectroscopic techniques that produce better readings, the parachor is no longer widely utilized.

A physiologically active molecule's parachor is related to its capacity to penetrate hydrophobic cell structures, notably cellular membranes. From the atoms and bonds that make up a steroid, the parachor may be computed. Analyzing the parachor values of several steroids reveals that these values are linked to a variety of biological processes from various separate sources that are distinct from one another. Numerous analytical techniques have shown that the parachors of steroids directly correlate with their respective anti-inflammatory potencies.

The surface tension of pure ionic liquids based on imidazolium is calculated using the parachor technique at various temperatures. A corresponding-states group-contribution approach is suggested to estimate the surface tension of ionic liquids for this prediction, covering a wide range of temperature and chain length.

Important Questions

  1. Mention the application of parachor value.

Ans: Parachor value can be used to estimate molecular volumes and to identify incomplete compounds by adding values for the atoms of the ingredients and structural characteristics

  1. How is parachor value related to surface tension and density of a liquid?

Ans: Parachor is directly proportional to the fourth root of a liquid’s surface tension and inversely proportional to the liquid’s density.


Parachor, also known as molar parachor or molecular parachor, is an empirical constant for a liquid that relates the surface tension to the molecular volume. It can be used to compare molecular volumes when the liquids have the same surface tension and to determine the partial structure of compounds by adding values for constituent atoms and structural features. This is the parachor definition in chemistry

Practice Questions

  1. Which of the properties is parachor related to?

    1. Surface tension

    2. Molar volume

    3. Both a and b

    4. None of the above

  1. Who developed an analytical solution for parachor as a function of temperature that is valid in all temperatures ranging from the melting point to the critical point?

    1. Escobedo and Mansoori

    2. S. Sugden

    3. Boudh-Hir and Mansoori

    4. None of the above


  1. (c)

  2. (a)

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FAQs on Parachor

1. What is the surface tension of a liquid?

Surface tension is described as a phenomenon that happens when the surface of a liquid comes into contact with another fluid (it can be a liquid as well). The least amount of surface area is often acquired by liquids. The liquid's surface acts like an elastic sheet. The forces of attraction between the particles in the supplied liquid as well as the forces of attraction of the solid, liquid, or gas in contact with it affect surface tension. The work or energy necessary to remove the surface layer of molecules in a unit area can be conceived of as being roughly equal to the energy responsible for the phenomena of surface tension.

2. What is the meaning of the term viscosity in liquids?

Viscosity is the term used to describe the degree of motion resistance found in most fluids. When fluid layers move relative to one another, viscosity develops. It measures flow resistance that results from internal friction between the fluid layers as they pass one another during fluid flow. The concept of viscosity may also be used to describe a fluid's thickness or resistance to items travelling through it. Strong intermolecular interactions provide a lot of internal friction in a fluid with a high viscosity, which prevents layers from moving past one another and opposes motion. As a result of its molecular structure, a fluid with low viscosity, on the other hand, flows without much resistance when in motion. Viscosity may also be seen in gases, however, it is less obvious in typical situations.

3. What is the difference between the density and relative density of a liquid?

The masses of bodies with the same volume but different suspensions are different. The physical size, also known as density, is a property of each material that is determined by mass and volume. Density is a measure of constancy that describes the ratio of mass to volume. A substance's relative density is determined by comparing its density at a given temperature to either water's density at that same temperature or another temperature that is used as a standard.