Molecular volumes of gases

Va, Vb = molecular volumes of gases, obtained by Kopp s law of additive volumes, cm /gm mol at normal boiling point. See Table 9-44. 

The mole is particularly useful when working with gas mixtures. It is based on Avogdro s law that equal volumes of gases at given pressure and temperature (pT) conditions contain equal number of molecules. Since this is so, then the weight of these equal volumes will be proportional to their molecular weights. The volume of one mole at any desired condition can be found by the use of the perfect gas law. 

These results and many similar ones led Avo-gadro to propose his famous hypothesis, as discussed in Section 2-2.3. The hypothesis states that equal volumes of gases contain equal numbers of molecules (at the same temperature and pressure). Therefore, the molecular weight of a gas... 

Regularities observed in the behavior of gases have contributed much to our understanding of the structure of matter. One of the most important regularities is Avogadro s Hypothesis Equal volumes of gases contain equal numbers of particles (at the same pressure and temperature). This relationship is valuable in the determination of molecular formulas—these formulas must be known before we can understand chemical bonding. 

If Vnh4ci, Yhc1, Ynh3 are the molecular volumes of the solid and two gases, respectively,... 

While studying gases in this chapter you will consider four main physical properties—volume, pressure, temperature, and amount—and their interrelationships. These relationships, commonly called gas laws, show up quite often on the AP exam, so you will spend quite a bit of time working problems in this chapter. But before we start looking at the gas laws, let s look at the Kinetic Molecular Theory of Gases, the extremely useful model that scientists use to represent the gaseous state. 

Julius) Lothar Meyer, 1830-1895. German chemist and physician. Professor of chemistry at Breslau and at Tubingen. Co-discoverer with Mendeleev of the periodic system of the elements. Some of his researches were on the gases of the blood, the molecular volumes of chemical compounds, atomic weights, a sensitive thermo-regulator, the paraffins, and the constitution of fuchsm. 

VA> VB = molecular volumes of diffusing and inert gases T = absolute temperature, °K... 

The Van der Waal s equation takes into account the deviations of real gases from the kinetic molecular theory of gases (nonzero molecular volume and nonelastic collisions). 

When we refer to the volume of a gas, we are in fact talking about the volume of the container. The definition of the volume of a gas is the space available for gas molecules to move around in. The kinetic molecular theory of gases assumes that the volume of each gas molecule is essentially zero. Thus, the amount of space for them to move around in is the volume of the container. For all gases, Vgas = the volume of the container holding the gas. (Do not confuse this with the molar volume of gases. You will learn about molar volume in Chapter 12.)... 

Italian chemist and physicist Amadeo Avogadro (1776-1856) proposed a correct molecular explanation for Gay-Lussac s law of combining volumes. His work provided a simple way to determine atomic weights and molecular weights of gases. 

In words, aP can be described as the fractional volume increase (dV/V) with respect to a temperature increase (dT) under isobaric conditions, while /3y is the corresponding fractional volume decrease (—dV/V) with respect to a pressure increase (dP) under isothermal conditions. Of course, both aP = ah P, T) and = fir(P, T) vary with P, T, as do other thermodynamic properties. Numerical values of aP, fiT (e.g., for 1 atm, 25°C) are often tabulated with other material properties, such as density, boiling point, or heat capacity, as unique fingerprints of a pure substance. [Throughout this book, experimental values are commonly drawn from standard sources, such as J. O. Hirschfelder, C. F. Curtiss, and R. B. Bird, Molecular Theory of Gases and Liquids (Wiley, New York, 1954) or any recent edition of the CRC Handbook of Chemistry and Physics (CRC Press, Boca Raton, FL).]... 

Section 12.1 introduces the concept of pressure and describes a simple way of measuring gas pressures, as well as the customary units used for pressure. Section 12.2 discusses Boyle s law, which describes the effect of the pressure of a gas on its volume. Section 12.3 examines the effect of temperature on volume and introduces a new temperature scale that makes the effect easy to understand. Section 12.4 covers the combined gas law, which describes the effect of changes in both temperature and pressure on the volume of a gas. The ideal gas law, introduced in Section 12.5, describes how to calculate the number of moles in a sample of gas from its temperature, volume, and pressure. Dalton s law, presented in Section 12.6, enables the calculation of the pressure of an individual gas—for example, water vapor— in a mixture of gases. The number of moles present in any gas can be used in related calculations—for example, to obtain the molar mass of the gas (Section 12.7). Section 12.8 extends the concept of the number of moles of a gas to the stoichiometry of reactions in which at least one gas is involved. Section 12.9 enables us to calculate the volume of any gas in a chemical reaction from the volume of any other separate gas (not in a mixture of gases) in the reaction if their temperatures as well as their pressures are the same. Section 12.10 presents the kinetic molecular theory of gases, the accepted explanation of why gases behave as they do, which is based on the behavior of their individual molecules. 

J. L. Gay-Lussac, Memoire sur la combinaison des substances gazeuses, les unes avec les autres, Memoires de la Societe d Arcueil 2, 1809, 207-234 translated in Foundations of the Molecular Theory, Alembic Club Reprints, no. 4 (Edinburgh, 1950), 8-24 M. P. Crosland, The Origins of Gay-Lussac s Law of Combining Volumes of Gases, Annals of Science 17, 1961, 1-26. 

Consideration of the bilayer membrane structures of mammalian cells led to a suggestion that anesthetics function by displacing the phospholipid layers, as long as the molecular volume of such compounds (gases) is larger than that of 02 and H20 (vapor). This would presumably disrupt certain membrane structures and thereby interfere with impulse transmission. 

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