Johannes van der Waals; the van der Waals Force

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Brigit
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Johannes van der Waals; the van der Waals Force

Unread post by Brigit » Wed Feb 26, 2020 8:41 pm

van der Waals, Johannes Diderik (1837-1923), a Dutch theoretical physicist, became famous for his work on the behavior of liquids and gases. He won the 1910 Nobel Prize in physics for developing the famous equation of state which bears his name. The equation takes into account the forces between the molecules of the gas. Van der Waals was born at Leiden, The Netherlands, on Nov 23, 1837. He served as professor of physics at Leiden from 1877 until his retirement in 1907. (World Book Encyclopedia 1962)
“Oh for shame, how these mortals put the blame upon us gods, for they say evils come from us, when it is they rather who by their own recklessness win sorrow beyond what is given…”
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Re: Johannes van der Waals; the van der Waals Force

Unread post by Brigit » Wed Feb 26, 2020 9:03 pm

VAN DER WAALS, JOHANNES DIDERIK (1837-1923), Dutch physicist, was born at Leiden, Nov. 23, 1837. At Leiden University he attracted scientific interest in 1873 by his thesis on the continuity of the liquid and gaseous conditions. He became professor of physics at the University of Amsterdam in 1877. He became known for his new derivation of an equation of state for gases, which went far beyond the laws of Robert Boyle and Joseph Gay-Lussac; his work in the kinetic theory of gases, and its application to fluids, and the extension of this, by means of "critical" values, to the "law of corresponding states." He retired from the University in 1907, was awarded the Nobel Prize in physics in 1910, and died at Amsterdam, on Mar. 9, 1923.



VAN DER WAALS' EQUATION, a relation between pressure, volume and temperature for pure gases and liquids formulated as follows:

(p + a/V^2) (V - b) = RT

Here p is the pressure; V is the volume occupied by one gram-molecular weight of the gas; T is the absolute temperature; and R is the gas constant, the same for all gases. The constnts a and b, the so-called van der Waals' constants, are characteristic of the gas in question.

The term (a/V^2) represents a pressure effect due to the attractions between the molecules which assist the externally applied pressure in compressing the gas;

b represents the small volume occupied by the molecules themselves which sets a limit to the compression experienced by the gas under very high pressures, since the free space subject to change is then only (V - b). At high tempreatures and low pressures, the equation reduces to the ideal gas law pV = RT. See Boyle's Law. L.O.C (National Encyclopedia 1944)
“Oh for shame, how these mortals put the blame upon us gods, for they say evils come from us, when it is they rather who by their own recklessness win sorrow beyond what is given…”
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Re: Johannes van der Waals; the van der Waals Force

Unread post by Brigit » Wed Feb 26, 2020 9:20 pm

WAALS, JOHANNES DIDERIK VAN DER [va'ls] (1837-1923), Dutch physicist and Nobel Prize winner in physics for 1910 for his laws of corresponding states and binary mixtures, was born in Leyden on Nov. 23, 1837.

After little early formal education, he studied science at the University of Leyden, where in 1873 he presented a doctor's thesis of unusual interest entitled On the Continuity of the Gaseous and Liquid States, which demonstrated his marked ability. In 1877 he was appointed to a chair of physics at the University Amsterdam, which he occupied until 1907.

Van der Waal's hypothesis of the continuity of the liquid and gaseous states was suggested by combining the kinetic theory of gases with La Place's theory of capillarity, an assumption which was strengthened by Andrews' observations on carbon dioxide. This led to his statement of the law of corresponding states, a law which was of great value to Dewar and Kammerling Onnes in their researches on the liquification of permanent gases.

Extending his researches into other fields, Van der Waals also developed a well-known equation which bears his name. He died on Mar. 9, 1923. See also Heat and Thermodynamics (States of Matter) H.N.A. (Collier's Encyclopedia 1957)
“Oh for shame, how these mortals put the blame upon us gods, for they say evils come from us, when it is they rather who by their own recklessness win sorrow beyond what is given…”
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Re: Johannes van der Waals; the van der Waals Force

Unread post by Brigit » Wed Feb 26, 2020 9:31 pm

van der Waals force in molecular solids
"Rare-gas solids (such as argon, krypton, and xenon) and some molecular solids (eg methane, CH4; hydrogen, H2; chlorine, Cl2) exhibit weak van der Waals or molecular boding in the solid state. Since the bonding occurs between atoms that have completely filled outer electron shells or non-ionized molecules, the crystals are only weakly bonded and are stable only at low temperatures.
The van der Waals bonding results from the displacement of the atomic nuclei from the center of the electron charge distribution in each atom, the displacement resulting when neutral atoms or molecules are brought close to each other. This induced charge displacement creates and electric dipole (ie, a body with two poles oppositely charged) that interacts with the adjacent induced dipoles to reduce the energy of the crystal and provide a small cohesive energy. The attractive interaction energy between the induced electric dipoles is of very short range and varies as the distance between atoms to the -6 power(or 1/distance^6). It is balanced by the repulsive interaction that occurs as the filled electron shells of the atoms begin to overlap on bringing the atoms closer together, a consequence of the increase in energy due to electrons having the same energy....
The nature of this type of molecular bonding leads to electrons that are localized at each atom and therefore to molecular solids that do not conduct electricity. They are insulators. Very large amounts of energy are required to excite an electron in such a solid from a localized state to a nonlocalized one."
Britannica 1988
emph added
“Oh for shame, how these mortals put the blame upon us gods, for they say evils come from us, when it is they rather who by their own recklessness win sorrow beyond what is given…”
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Re: Johannes van der Waals; the van der Waals Force

Unread post by Brigit » Wed Feb 26, 2020 9:35 pm

van der Waals forces in gases
"A knowledge of the distribution function is essential for any microscopic theory of a gas; however, its determination involves postulating some mathematical description of a gas particle and how a gas-particle collision actually occurs. In any real gas, even a binary collision -- one between two particles only -- is a complicated process, because each particle is surrounded by a force field that varies in space. This force field is such that it attracts another particle when that other particle is relatively far away but repels it when the other particle comes relatively close. That these intermolecular forces exist is evident from the fact that gases do not condense into liquids, a phenomenon that cannot be explained except as a consequence of attractive forces at work between the particles. In addition, liquids strongly resist being compressed, which must be evidence of the repulsive forces.
The long-range attractive forces, called van der Waals forces, arise from the electrostatic interactions between the whole particles. Short-range forces arise when the electron clouds that surround the nuclei of atoms in a molecule overlap. These short-range forces are called valence forces, and they become stronger than the van der Waals forces when the two particles come sufficiently close together in a binary collision."
(Britannica 1988)
“Oh for shame, how these mortals put the blame upon us gods, for they say evils come from us, when it is they rather who by their own recklessness win sorrow beyond what is given…”
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Re: Johannes van der Waals; the van der Waals Force

Unread post by Brigit » Wed Feb 26, 2020 9:55 pm

WAALS, vals, Johannes Diderik van der, Dutch physicist: b. Leyden, Netherlands Nov. 23, 1837; d. Amsterdam, March 9, 1923.

After taking his doctorate at the University of Leyden in 1873 and teaching in various high schools, he was appointed professor of physics at the University of Amsterdam, where he remained until 1907.

Known chiefly for his works on the continuity of the liquid and gaseous states, he was led to the statement of the law of corresponding states by combining the kinetic theory of gases and La Place's theory of capillarity. He also developed van der Waals' equation. In 1910 he was awarded the Nobel Prize for physics for his laws of corresponding states and binary mixtures. He was the author of several works on gases.
(Encyclopedia Americana 1959)
“Oh for shame, how these mortals put the blame upon us gods, for they say evils come from us, when it is they rather who by their own recklessness win sorrow beyond what is given…”
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Johannes van der Waals; the van der Waals Force

Unread post by Brigit » Mon Oct 31, 2022 6:39 pm

F&W 1996

Gases.
The Ideal Gas Law.
The Kinetic Theory of Gases.
Van der Waals equation. "The ideal gas equation of state is only approximately correct. Real gases do not behave exactly as predicted. In some cases the deviation can be extremely large. For example, ideal gases could never become liquids or solids, no matter how much they were cooled or compressed. Thus, modifications of the ideal gas law, PV = RT, were proposed. Particularly useful and well known is the van der Waals equation of state: (P + a/V^2) (V - b) = RT, where a and b are adjustable parameters determined from experimental measurements carried out on actual gases. They are material parameters rather than universal constants, in the sense that their values vary from gas to gas.

The van der Waals equation also has a microscopic interpretation. Molecules interact with one another. The interaction is strongly repulsive in close proximity, becomes mildly attractive at intermediate range, and vanishes at long distance. The ideal gas law must be corrected when attractive and repulsive forces are considered. For example, the mutual repulsion between molecules has the effect of excluding certain territory around each molecule from intrusion by its neighbors. Thus, a fraction of space becomes unavailable to each molecule as it executes random motion. In the equation of state, a volume of exclusion (b) should be subtracted from the volume of the container (V); thus, (V - b).

Phase transitions. At low temperatures (reduced molecular motion) and at high pressures or reduced volumes (reduced intermolecular spacing), the molecules in a gas come under the influence of one another's attractive force. Under certain critical conditions, the entire system enters a high-density bound state and acquires a bounding surface. This signifies the onset of the liquid state. The process is known as a phase transition. The van der Waals equation permits such a phase transition. It also describes a two phase coexistence region that terminates on a critical point (q.v.), above which no physical distinction can be found between the gas and liquid phases. These phenomena are consistent with experimental observations. For actual use one has to go to equations that are more sophisticated than the van der Waals equation.

Improved understanding of the properties of gases over the past century has led to the large-scale exploitation of the principles of physics, chemistry, and engineering for industrial and consumer applications."







* "The van der Waals bonding results from the displacement of the atomic nuclei from the center of the electron charge distribution in each atom, the displacement resulting when neutral atoms or molecules are brought close to each other. This induced charge displacement creates and electric dipole (ie, a body with two poles oppositely charged) that interacts with the adjacent induced dipoles to reduce the energy of the crystal and provide a small cohesive energy." Br1988
“Oh for shame, how these mortals put the blame upon us gods, for they say evils come from us, when it is they rather who by their own recklessness win sorrow beyond what is given…”
~Homer

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