Enthalpy

About: Enthalpy is a research topic. Over the lifetime, 21390 publications have been published within this topic receiving 467399 citations.

Dependence of the Fictive Temperature of Glass on Cooling Rate

Abstract: An equation derived by Ritland relating the cooling rate and fictive temperature for glasses without memory is extended to those with memory, i.e. those which exhibit a spectrum of relaxation times. Provided that the spectrum of relaxation times is temperature-independent, the limiting fictive temperature, T′f, obtained when a glass is cooled through the transition region, is shown to be related to the cooling rate, q, by d In |q|/d(1/T'f)=-Δh★/R where R is the ideal gas constant and Δh★ the activation enthalpy for the relaxation times controlling the structural relaxation. Values of T′f vs q obtained from enthalpy measurements by differential scanning calorimetry are presented for B2O3, 0.4Ca(NO3)2—0.6KNO3, and borosilicate crown glasses; Δh★ is equal, within experimental error, to the activation enthalpy for shear viscosity. Values of T′f from volume and enthalpy measurements obtained at the same cooling rate for the borosilicate crown glass are equal.

Standard Electrode Potentials and Temperature Coefficients in Water at 298.15 K

Abstract: A great deal of solution chemistry can be summarized in a table of standard electrode potentials of the elements in the solvent of interest. In this work, standard electrode potentials and temperature coefficients in water at 298.15 K, based primarily on the ‘‘NBS Tables of Chemical Thermodynamic Properties,’’ are given for nearly 1700 half‐reactions at pH=0.000 and pH=13.996. The data allow the calculation of the thermodynamic changes and equilibrium constants associated with ∼1.4 million complete cell reactions over the normal temperature range of liquid water. Estimated values are clearly distinguished from experimental values, and half‐reactions involving doubtful chemical species are duly noted. General and specific methods of estimation of thermodynamic quantities are summarized.

The Proton's Absolute Aqueous Enthalpy and Gibbs Free Energy of Solvation from Cluster-Ion Solvation Data

Abstract: A method is presented to determine the absolute hydration enthalpy of the proton, ΔHaq°[H+], from a set of cluster-ion solvation data without the use of extra thermodynamic assumptions. The absolute proton hydration enthalpy has been found to be ∼50 kJ/mol different than traditional values and has been more precisely determined (by about an order of magnitude). Conventional ion solvation properties, based on the standard heat of formation of H+(aq) set to zero, have been devised that may be confusing to the uninitiated but are useful in thermochemical evaluations because they avoid the unnecessary introduction of the larger uncertainties in our knowledge of absolute values. In a similar strategy, we have motivated the need for a reassessment of ΔHaq°[H+] by the trends with increased clustering in conventional cluster-ion solvation enthalpy differences for pairs of oppositely charged cluster ions. The consequences of particular preferred values for ΔHaq°[H+] may be evaluated with regard to cluster-ion prop...