Law of Avogadro

Discuss molecules and molecular weight in the light of the Laws of Avogadro and Gay-Lussac, vapor density, vapor tension, elevation of the boiling point, and depression of the freezing point. 

Law of Avogadro equal volumes of gases at constant temperature and pressure contain the same number of molecules whether the gases are the same or different. 22.4 L of any gas contains 6.02 x 1023 molecules. See Avogadro s law mole. 

Both the law of Avogadro and that of Dulong and Petit have, of course, been much used in the determination of atomic weights originally their use was only for an approximate estimation, while the exact value was then found by chemical analysis. 

From the practical point of view, we must not give undue weight to this good agreement, which is probably to be ascribed to the fact that exact results have been obtained for the specific heat of silver by different observers but it may well serve to indicate afresh that the theoretical foundations for the law of Dulong and Petit are now just as well established as those for the law of Avogadro have been for many years. 

Gases and Vapoks.— The specific gravities of gases ami vapors are of great importance in theoretical chemistry, as from them we can determine molecular weights, in obedience to the law of Avogadro (p. 14). 

This idea was extended by Mendeleeff into what he called the law of Avogadro-Gerhardt , also named the Mendeleeff-Gerhardt Law , that gases always react in equal volumes, e.g. ... 

The properties of hydrocarbon gases are relatively simple since the parameters of pressure, volume and temperature (PVT) can be related by a single equation. The basis for this equation is an adaptation of a combination of the classical laws of Boyle, Charles and Avogadro. 

The behavior of all gases that obey the laws of Boyle and Charles, and Avogadro s hypothesis, can be expressed by the ideal gas equation ... 

We can evaluate the constant (kik2k3) in this equation by taking advantage of Avogadro s law, which states that equal volumes of all gases at the same temperature and pressure contain the same number of moles. For this law to hold, the constant must be the same for all gases. Ordinarily it is represented by the symbol R. Both sides of the equation are multiplied by P to give the ideal gas law... 

Avogadro suggested this relationship to explain the law of combining volumes. Today it seems obvious. For example, in the reaction... 

Stanislao Cannizzaro, professor of chemistry at f the University of Genoa. At a conference held in I Karlsruhe in 1860, he persuaded the chemistry community of the validity of Avogadro s law and showed how it could be used to determine molar and atomic masses, i The quantity now called "Avogadro s number (6.02 x 10 /mol) was first estimated in = 1865, nine years after Avogadro died. Not until... 

Kinetic theory A theory of matter based on the mathematical description of the relationship between pressures, volumes, and temperatures of gases (PVT phenomena). This relationship is summarized in the laws of Boyle s law, Charle s law, and Avogadro s law. 

Background Avogadro s law (Vin2 = V2ni), where moles, n = mw (grams/mole) exPresses the relationship between molar mass, the actual mass and the number of moles of a gas. The molar volume of a gas at STP, VSTP is equal to the volume of the gas measured at STP divided by the number of moles VSTp = pp. Dalton s Law of Partial Pressure (Ptotai = Pi + P2 + P3 +. ..) and the derivation, Pi = pp Ptotai will also be used in this experiment to predict the volume occupied by one mole of hydrogen gas at STP. 

The combined gas law and Avogadro s relationship can then be combined into the ideal gas equation, which incorporates the pressure, volume, temperature, and amount relationships of a gas. 

The values of P, T, and n may be used to determine the volume of a gas. If this volume is to be used with Avogadro s law of 22.4 L/mol, the combined gas law must be employed to adjust the volume to STE This equation will use the measured values for P and Talong with the calculated value of V. These values are combined with STE conditions (0°C (273.15 K) and 1.00 atm) to determine the molar volume of a gas. 

CANNIZZARO, STANISLAO (1826-1910). Born in Italy, lie extended the research of Avogadro on the molecular concentration of gases and thus was able to prove the distinction between atoms and molecules. His investigations of atomic weights helped to helped lo make possible the discovery of the periodic law hy Mendeleyev. His research in organic chemistry led to the establishment of the Cannizzaro reaction involving the oxidation reduction of an aldehyde in the presence of concentrated alkali. 

I cu ft of O2 10 form only 2 cubic feet of HiO. This relationship is based on Avogadro s law and the law of combining weights. 

The ideal gas law can be rearranged in different ways to take the form of Boyle s law, Charles law, or Avogadro s law. 

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