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Enthalpy determination from

Probably the most significant comparisons which can be made are of values of properties determined from calorimetric measurements with values calculated from adsorption isotherms. Two general methods are available for the comparison of values of enthalpies determined from experiments of the two types. One involves two differentiations The change in the partial molal enthalpy, AH2, of X2, for Process 4, is determined from the differentiation with respect to n2/n1 of the integral heat of adsorption measured in a series of calorimetric experiments of the type represented by Equation 1. The values of the differential heats of adsorption (heats corresponding to the differential Process 4) are compared with values determined from the temperature variation of AG2/T for a series of values of n2/n in Process 4. This type of comparison has been made successfully by several groups of authors (3, 5, 10). [Pg.354]

An alternative is the isothermal dilution calorimeter. For an endothermic system, one component is slowly injected into the second component with the simultaneous addition of electrical energy sufficient to maintain the calorimeter isothermal. The addition is discontinued at any desired composition and the excess enthalpy determined from the initial amount of substance of component B in the vessel, the amount of substance of component A injected, and the electrical energy added to maintain isothermal conditions. The apparatus is normally designed so that the entire composition range can be covered in two experimental runs. For exothermic systems it is possible to add electrical energy... [Pg.30]

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]. [Pg.404]

The reaction enthalpies determined from G2 and MP4/6-31 lG(2df,2pd) calculations are generally in good accord... [Pg.1444]

The enthalpy determined from the variation of equilibrium constant with temperature is equal to the AH directly obtained from calorimetric measurements. [Pg.311]

The enthalpy determined from the relationship iUustrated by Figure 10.2 is... [Pg.436]

The enthalpy for the formation of Cr2(OH)2 can be derived from the stability constant data of Thompson (1964) and Stiinzi et al. (1989) determined from experiments utilising a medium of 1.0 mol 1 NaClO. These experiments covered the relatively narrow temperature range of25-67.5 °C, but over this range the stability constants were found to vary linearly with the reciprocal of absolute temperature (although with a relatively high uncertainty). The relationship between the stability constants and temperature is illustrated in Figure 11.28. The enthalpy determined from this relationship is... [Pg.547]

As shown in Section 11.3.2.1, the stabiUty constant determined at zero ionic strength and 25 C is log j = —(3.60 0.07). The analyses shown in Section 11.3.2.2 indicate that the enthalpies determined from data at zero ionic strength (Bjerrum, 1907 Emerson and Graven, 1959 Tsuchiya and Umayahara,... [Pg.553]

Enthalpies are referred to the ideal vapor. The enthalpy of the real vapor is found from zero-pressure heat capacities and from the virial equation of state for non-associated species or, for vapors containing highly dimerized vapors (e.g. organic acids), from the chemical theory of vapor imperfections, as discussed in Chapter 3. For pure components, liquid-phase enthalpies (relative to the ideal vapor) are found from differentiation of the zero-pressure standard-state fugacities these, in turn, are determined from vapor-pressure data, from vapor-phase corrections and liquid-phase densities. If good experimental data are used to determine the standard-state fugacity, the derivative gives enthalpies of liquids to nearly the same precision as that obtained with calorimetric data, and provides reliable heats of vaporization. [Pg.82]

The enthalpy changes due to dimerization are determined from the van t Hoff relation. For a dimerization reaction between species i and j... [Pg.136]

FIGURE 3 20 The enthalpy difference between as- and trans 1 2 dimethylcyclopropane can be determined from their heats of combustion Van der Waals strain between methyl groups on the same side of the ring make the cis isomer less stable than the trans... [Pg.125]

Other crystallization parameters have been determined for some of the polymers. The dependence of the melting temperature on the crystallization temperature for the orthorhombic form of POX (T = 323K) and both monoclinic (T = 348K) and orthorhombic (T = 329K) modifications of PDMOX has been determined (284). The enthalpy of fusion, Aff, for the same polymers has been determined by the polymer diluent method and by calorimetry at different levels of crystallinity (284). for POX was found to be 150.9 J/g (36.1 cal/g) for the dimethyl derivative, it ranged from 85.6 to 107.0 J/g (20.5—25.6 cal/g). Numerous crystal stmcture studies have been made (285—292). Isothermal crystallization rates of POX from the melt have been determined from 19 to —50 C (293,294). Similar studies have been made for PDMOX from 22 to 44°C (295,296). [Pg.368]

Studies on metal-pyrazole complexes in solution are few. The enthalpy and entropy of association of Co(II), Ni(II), Cu(II) and Zn(II) with pyrazole in aqueous solution have been determined by direct calorimetry (81MI40406). The nature of the nitrogen atom, pyridinic or pyrrolic, involved in the coordination with the metal cannot be determined from the available thermodynamic data. However, other experiments in solution (Section 4.04.1.3.3(i)) prove conclusively that only the N-2 atom has coordinating capabilities. [Pg.226]

The diagram in Fig. 11-101 presents enthalpy data for LiBr-water solutions. It is needed for the thermal calculation of the cycle. Enthalpies for water and water vapor can be determined from the table or properties of water. The data in Fig. 11-101 are apphcable to saturated or subcooled solutions and are based on a zero enthalpy of liquid water at 0°C and a zero enthalpy of solid LiBr at 25°C. Since... [Pg.1118]

The enthalpy of the adsorption of chlorobenzene was determined from the temperature-dependence of the SERS intensities [4.301]. [Pg.263]

The humidity at the temperature of 25 °C corresponding to this enthalpy is determined from the equation... [Pg.90]

The amonnt of energy that can be released from a given chemical reaction is determined from the energies (enthalpies of formation) of the individnal reactants and prodncts. Enthalpies are nsnally given for snbstances in their standard states, which are the stable states of pnre snbstances at atmospheric pressnre and at 25°C. The overall heat of reaction is the difference between the snms of the standard enthalpies of formation of the prodncts... [Pg.53]

Enthalpy changes for biochemical processes can be determined experimentally by measuring the heat absorbed (or given off) by the process in a calorimeter (Figure 3.2). Alternatively, for any process B at equilibrium, the standard-state enthalpy change for the process can be determined from the temperature dependence of the equilibrium constant ... [Pg.58]

FIGURE 3.3 The enthalpy change, ATT, for a reaction can be determined from the slope of a plot of R In versus l/T. To illns-trate the method, the values of the data points on either side of the 327.5 K (54.5 C) data point have been nsed to calculate ATT at 54.5 C. Regression analysis would normally be preferable. (Adapted from Brandts, ]. F., 1964. Tim thermo-dynamics of protein denatnration. I. The denatnration of ehy-motrypsinogen. om Q.7A of the American Chemical Society m 429 -430L)... [Pg.59]

M. Migschitz and W Pfeiler, Vacancy activation enthalpies of Au-Fe alloys determined from SRO-induced resistivity changes, A/a/. Sci. Eng. A206 I55 (1996)... [Pg.230]

At given inlet conditions, determine inlet entropy (s) and enthalpy (h) from Mollier Diagram ... [Pg.495]

Thermodynamic quantities for a system may be determined from the van t Hoff equation Eq.(3), which defines the equilibrium constant, K, in terms of the reaction enthalpy, AH and the temperature, T. [Pg.210]

The enthalpy of the phase conversion can be determined from Eq.(6) by plotting the log of the absorption or desorption plateau pressure, P lnleau, against the reciprocal temperature as indicated in Fig. 2. When the solubility of hydrogen in the metal (or) phase is small, then AHplM AH(, where AH( is essentially the enthalpy of forma... [Pg.211]

Standard enthalpies of formation are commonly determined from combustion data by using Eq. 20. The procedure is the same, but the standard reaction enthalpy is known and the unknown value is one of the standard enthalpies of formation. [Pg.372]

The solubilities of the ionic halides are determined by a variety of factors, especially the lattice enthalpy and enthalpy of hydration. There is a delicate balance between the two factors, with the lattice enthalpy usually being the determining one. Lattice enthalpies decrease from chloride to iodide, so water molecules can more readily separate the ions in the latter. Less ionic halides, such as the silver halides, generally have a much lower solubility, and the trend in solubility is the reverse of the more ionic halides. For the less ionic halides, the covalent character of the bond allows the ion pairs to persist in water. The ions are not easily hydrated, making them less soluble. The polarizability of the halide ions and the covalency of their bonding increases down the group. [Pg.1014]


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Enthalpy determination

The Temperature Dependence of Reaction Enthalpies Can Be Determined from Heat Capacity Data

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