Measurement thermodynamic state functions

In the broadest sense, thermodynamics is concerned with mathematical relationships that describe equiUbrium conditions as well as transformations of energy from one form to another. Many chemical properties and parameters of engineering significance have origins in the mathematical expressions of the first and second laws and accompanying definitions. Particularly important are those fundamental equations which connect thermodynamic state functions to real-world, measurable properties such as pressure, volume, temperature, and heat capacity (1 3) (see also Thermodynamic properties). 

Transfer functions can also be defined for the thermodynamic state functions AH° and AS° [102], The ease of calorimetric measurements has made the standard molar transfer enthalpy, AH X,1 II), readily available. If both transfer Gibbs energies and... 

The thermodynamic state function entropy, S, is a measure of the disorder of the system. The greater the disorder of a system, the higher is its entropy. For any substance, the particles are more highly ordered in the solid state than in the liquid state. These, in turn. 

Applying Eq. (A.7) to thermodynamic state functions (instead of a general function /) gives rise to the celebrated Maxwell relations. They can be used to express certain quantities that are hard to measure or control in a laboratory experiment in terms of mechanical variables such as a set of stresses and strains and their temperature and density dependence. 

We encounter another thermodynamic state function, free energy (or Gibbs free energy), a measure of how far removed a system is from equilibrium. The change in free energy measures the maximum amount of useful work obtainable from a process and tells us the direction in which a chemical reaction is spontaneous. 

Section 19.5 The Gibbs free energy (or just free energy), G, is a thermodynamic state function that combines the two state functions enthalpy and entropy G = H — TS. For processes that occur at constant temperature, AG = AH — TAS. For a process or reaction occurring at constant temperature and pressiue, the sign of AG relates to the spontaneity of the process. When AG is negative, the process is spontaneous. When AG is positive, the process is nonspontaneous the reverse process is spontaneous. At equilibrium the process is reversible and AG is zero. The free energy is also a measure of the maximum useful work that can be performed by a system in a spontaneous process. 

Entropy (S) A thermodynamic state function that measures the dispersal of energy and the dispersal of matter (disorder) of a system. 

Measurements of specific heat capacities are of major importance because the thermodynamic state functions can be calculated from them (see Section 3.1.6). 

Transfer functions can also be defined for the other thermodynamic state functions. Since enthalpy changes are often conveniently measurable, the transfer enthalpy, is perhaps the most widely used function. From the second law of thermodynamics, the transfer entropy function is given by Equation 6.9. 

Entropy is a thermodynamic state function (often described as a measure of disorder) that is related to the number of microstates in a system. 

From these measured properties, thermodynamic state functions (enthalpies of sublimation, entropies, and free-energy functions) have been derived. For several actinides, these properties have been critically reviewed by Hultgren et al. [24] and more recently by Getting, Rand, and Ackermann [14]. The latter compilation includes properties for the metallic state and for ideal gas to 5(XX) K for the elements Th through Cm. Sublimation enthalpies (determined from measured vaporization behavior for Th through Es) and standard entropies (determined from measured heat capacities for Th through Am) of the actinide metals are compiled in Table 17.1. Sublimation enthalpies have been correlated with metal structures and electronic energy levels [27,28]. 

Entropy is a thermodynamic state function that measures how dispersed or spread out a system s energy is. 

The lattice enthalpy of a solid cannot be measured directly. However, we can obtain it indirectly by combining other measurements in an application of Hess s law. This approach takes advantage of the first law of thermodynamics and, in particular, the fact that enthalpy is a state function. The procedure uses a Born-Haber cycle, a closed path of steps, one of which is the formation of a solid lattice from the gaseous ions. The enthalpy change for this step is the negative of the lattice enthalpy. Table 6.6 lists some lattice enthalpies found in this way. 

A very important characteristic of entropy that is not immediately obvious from Eq. 1 but can be proved by using thermodynamics is that entropy is a state function. This property is consistent with entropy being a measure of disorder, because the disorder of a system depends only on its current state and is independent of how that state was achieved. 

Entropy is a measure of disorder according to the second law of thermodynamics, the entropy of an isolated system increases in any spontaneous process. Entropy is a state function. 

Entropy, which has the symbol S, is a thermodynamic function that is a measure of the disorder of a system. Entropy, like enthalpy, is a state function. State functions are those quantities whose changed values are determined by their initial and final values. The quantity of entropy of a system depends on the temperature and pressure of the system. The units of entropy are commonly J K1 mole-1. If S has a ° (5°),... 

The interfacial tension of mixed adsorbed films of 1-octadecanol and dodecylammonium chloride has been measured as a function of temperature at various bulk concentrations under atmospheric pressure. The transition interfacial pressure of 1-octadecanol film has been observed to increase with the addition of dodecylammonium chloride and then to disappear. The interfacial pressure vs mean area per adsorbed molecule curves have been illustrated at a constant mole fraction of adsorbed molecules. With the aid of the thermodynamic treatment developed previously, we find that the mutual interaction between 1-octadecanol and dodecylammonium chloride molecules in the expanded state is similar in magnitude to the interaction between the scime kind of film-forming molecules. 

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