Thermal Expansion of Gases

No tables of the coefficients of thermal expansion of gases are given in this edition. The coefficient at constant pressure, l/v(dx /dT)r for an ideal gas is merely the reciprocal of the absolute temperature. For a real gas or liquid, both it and the coefficient at constant volume, /p ((t[i/dT), should be calculated either from the equation of state or from tabulated PVT data. 

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These expressions show that a deformed polymer network is an extremely anisotropic body and possesses a negative thermal expansivity along the orientation axis of the order of the thermal expansivity of gases, about two orders higher than that of macromolecules incorporated in a crystalline lattice (see 2.2.3). In spite of the large anisotropy of the linear thermal expansivity, the volume coefficient of thermal expansion of a deformed network is the same as of the undeformed one. As one can see from Eqs. (50) and (51) Pn + 2(iL = a. Equation (50) shows also that the thermoelastic inversion of P must occur at Xim (sinv) 1 + (1/3) cxT. It coincides with F for isoenergetic chains [see Eq. (46)]. 

A 500-mL round-bottomed flask is fitted with a 30-cm long tube for use as an air-cooled reflux condenser. This tube is closed by a stopcock fitted with a rubber breathing bag, allowing for thermal expansion of gases but maintaining the inertness of the atmosphere inside. 

Another reason is that the (thermodynamic) temperature T can be defined easily based on entropy, but only in a temporary form and awkwardly without this concept. Without entropy, this definitirMi is commonly achieved via the thermal expansion of gases. However, one usually forgoes demonstrating that the temperature 0 defined this way acmaUy corresponds to the thermodynamic T. Let us overlook this difficulty When the equation dg = Td5e above is solved for d5e and then integrated, the result is ... 

Gay-Lussac (Figure 5.6) was the most famous of the prot6g6s of Berthollet. After distinguishing himself at the Ecole Polytechnique, Gay-Lussac went to Arcueil in 1801 to work as Berthollet s assistant, and Berthollet was to play an important role in Gay-Lussac s professional advancement. Gay-Lussac s first major research was on the thermal expansion of gases (Chapter 13), and his work was considerably more accurate than a similar study performed at about the same time by Dalton. 

The law of partial pressures, Eq. (3.3.7), was observed in 1801 by John Dalton (1766-1844), a British chemist and physicist. He worked on the constitution of mixed gases, on the vapor pressure of liquids, and on the thermal expansion of gases. His most important investigations are those concerned with the atomic theory in chemistry, which can be summarized as follows (i) Elements are made of tiny particles called atoms, (ii) Atoms of a given element are identical and different from those of other elements, (iii) Atoms of one element can combine with atoms of other elements to form compounds that always have the same relative numbers of types of atoms, (iv) Atoms cannot be created, divided into smaller particles, or destroyed in the chemical process. These statements of Dalton s theory are to a large extent still true. Today we know that his statement Atoms cannot be created, divided. .. is inconsistent with nuclear fusion and fission, and his statement All atoms of a given element are identical is also not precisely true, as there are different isotopes of an element. Dalton also did research into color blindness, which is sometimes called Daltonism in his honor. 

The thermal expansion of gases, liquids, and solids is still used to build simple thermometers, which indicate the temperature in the direct proximity of the measurement location. The most usual measuring media are alcohol and mercury. However, mercury poses a health hazard and should only be used when necessary. 

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