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,
$P\,=\,{{\gamma}^{1/4}}\frac{M}{({{\rho}_{L}}-{{\rho}_{V}})}\,=\,{{\gamma }^{1/4}}V$
Where,
$\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
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
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.
Summary
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
Which of the properties is parachor related to?
Surface tension
Molar volume
Both a and b
None of the above
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?
Escobedo and Mansoori
S. Sugden
Boudh-Hir and Mansoori
None of the above
Answers
(c)
(a)
FAQs on Parachor
1. What is parachor in chemistry?
Parachor is a physical property of a liquid that connects its surface tension with its molecular volume. It represents a hypothetical volume of a substance that would exist if its surface tension were equal to one. This value is particularly useful for studying and comparing the molecular structure of different liquids.
2. How is the parachor value of a substance calculated?
The parachor (P) is calculated using the Sugden equation: P = M × γ^(1/4) / (D - d). In this formula:
- M is the molar mass.
- γ (gamma) is the surface tension of the liquid.
- D is the density of the liquid.
- d is the density of the vapour in equilibrium with the liquid.
3. What are the main applications of parachor in chemistry?
Parachor is a valuable tool used primarily to:
- Help determine the molecular structure of chemical compounds.
- Distinguish between different isomers of a compound, such as keto-enol tautomers.
- Confirm the presence of specific structural features, like rings or double bonds, within a molecule.
- Calculate the approximate surface tension of a liquid if its density and structure are known.
4. Why is parachor considered both an additive and a constitutive property?
Parachor has a dual nature which makes it so useful:
- It is an additive property because the total parachor of a molecule can be calculated by summing the specific parachor values of each atom it contains.
- It is also a constitutive property because its value depends on how the atoms are arranged and bonded, such as the presence of single bonds, double bonds, or ring structures. Each of these structural elements contributes a specific value to the total.
5. How does parachor help relate a liquid's surface tension to its structure?
Parachor provides a bridge between a large-scale physical property (surface tension) and the microscopic molecular structure. By calculating the parachor from experimental values of surface tension and density, and comparing it to the theoretical value calculated from its proposed structure (by adding atomic and bond values), scientists can verify if the proposed structure is correct.
6. What is the standard unit used to express parachor?
The unit of parachor is derived from its formula. In the CGS (centimetre-gram-second) system, the unit is cm³·g^(1/4)·s⁻²·mol⁻¹. While it has a defined unit, parachor values are often used as dimensionless numbers for comparing the structures of different compounds.
7. How does parachor differ from molar volume?
While both concepts relate to volume, they are different. Molar volume is the actual, physical volume that one mole of a substance occupies at a specific temperature and pressure. In contrast, parachor is a constant, calculated volume that is independent of temperature. It's a theoretical value used for structural comparison, not a measure of physical space occupied.
