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Standard molar entropy

About: Standard molar entropy is a research topic. Over the lifetime, 1586 publications have been published within this topic receiving 29886 citations.


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TL;DR: In this article, the authors derived equilibrium constants for the systems containing propanol + propanal, and butanol + butanal from measurements of the composition of mixtures obtained when the vapours were passed with hydrogen over a catalyst held at a measured temperature.
Abstract: Equilibrium constants for the systems containing propanol + propanal, and butanol + butanal were derived from measurements of the composition of mixtures obtained when the vapours were passed with hydrogen over a catalyst held at a measured temperature. Equations expressing the changes in Gibbs energy, enthalpy and entropy of the reactions over a range of temperature were calculated from the measurements, with the aid of heat capacity data. By coupling thermodynamic data for the reactions with thermodynamic data for the appropriate alcohol, the standard heats of formation of liquid propanal and butanal were calculated to be –52.64 and –56.90 kcal mole –1 respectively, and the standard entropies of liquid propanal and butanal were calculated to be 48.2 and 59.4 cal deg–1. mole–1 respectively. The above values for the heats of formation agree with values derived from heat-of-combustion measurements; the value for propanal indicates an unusual thermochemical stability in this compound. The value derived for the standard entropy of butanal agrees with a published value obtained by low-temperature calorimetry, but the value derived for the entropy of propanal (ideal gas) does not agree with a published value obtained by statistical mechanics.

28 citations

Journal ArticleDOI
TL;DR: In this paper, a new group of low viscosity hydrophobic trioctylammonium-based protic ionic liquids (PILs) with 2-naphthoate, 4-tert-butylbenzoate, 2-hexyldecanoate, and 4-phenylbutanoate anions were synthesized.

28 citations

Journal ArticleDOI
TL;DR: The correlation between the degree of proton transfer and aqueous ΔpKa or ΔrHmθ was investigated and it was found that in some special cases, ΔrSmθ, especially the entropy change of symmetry, also plays an important role in affecting thedegree ofProton transfer.
Abstract: The degree of proton transfer and thermodynamic parameters of six acetate-based protic ionic liquids (PILs) were measured using nuclear magnetic resonance spectroscopy and calculated by van't Hoff analytical method, respectively. The degree of proton transfer of these PILs at 298 K spread over a large range, which is from 39.6% (1-methylpyrrolidinium acetate, [MpyrH][AcO]) to 94.4% (1-butylimidazolium acetate, [BuimH][AcO]). The calculated standard enthalpy change of the reaction (ΔrHmθ) is from -23.30 to -7.80 kJ mol-1 and the standard entropy change of the reaction (ΔrSmθ) is from -42.70 to -8.07 J mol-1 K-1. The correlation between the degree of proton transfer and aqueous ΔpKa or ΔrHmθ was investigated as well. Furthermore, in some special cases, ΔrSmθ, especially the entropy change of symmetry, also plays an important role in affecting the degree of proton transfer.

28 citations

Journal ArticleDOI
TL;DR: The characterization of recently synthesized (Pro‐Pro‐Gly)n, n = 7, 8 is described, along with melting profile studies of its association equilibrium, and thermal quenching studies of the kinetics ofIts association reaction.
Abstract: The characterization of recently synthesized (Pro-Pro-Gly)n, n = 7, 8 is described, along with melting profile studies of its association equilibrium, and thermal quenching studies of the kinetics of its association reaction. The order of the kinetic reaction is about 3, implying that three peptide chains are involved in the activated state of the rate-limiting step. The reaction rate was found to exhibit a negative temperature coefficient. With the (Pro-Pro-Gly)7 peptide, the concentration dependence of the (Pro-Pro-Gly)n association equilibrium was observed for the first time. Detailed thermodynamic analysis for these n = 7, 8 data, together with literature data for n = 10, 15, 20 were carried out for both the simple “all-or-none” binding model and for a series of complex equilibrium models. For the latter, all of the (Pro-Pro-Gly)n data (in 10% acetic acid) are fit best with a maximally cooperative near-neighbor model with a standard enthalpy change ΔH = −650 cal/mole of residues, and a standard entropy change ΔS = −14.63 −10/n cal/deg-mole of residues, wherein the −10 eu represents an end-effect contribution to the binding free energy. With regard to optical rotatory properties and thermodynamic parameters, the data for the new n = 7, 8 peptides match rather well with the literature data for the n = 10, 15, and 20 peptides. The enthalpic stabilization per residue of the triple-helical form of (Pro-Pro-Gly)n was nearly an order of magnitude smaller than the enthalpic stabilization per additional proline obtained from direct calorimetric measurements on native collagens of different (and much lower) proline contents by Privalov and Tiktopulo. [Biopolymers (1970) 9, 127–139.] Possible explanations for this phenomenon are discussed.

27 citations

Journal ArticleDOI
TL;DR: In this paper, the solubilities and solubility products of 14 lanthanon trifluorides (LnF3· 0.5H2O) have been determined using conductometric, potentiometric and radiometric techniques.
Abstract: Solubilities and solubility products of 14 lanthanon trifluorides (LnF3· 0.5H2O) have been determined using conductometric, potentiometric and radiometric techniques. The solubilities and the averages of selected pKsp values from literature and from our own work, that do not differ by more than one unit, show three maxima when plotted against the atomic number of lanthanons. Standard enthalpy change measured from the temperature-dependence plots of Ksp and the free-energy change calculated from Ksp of the trifluorides fall within the range 30–60 kJ mol–1 and 78–103 kJ mol–1, respectively, in most cases. Standard entropy change calculated from the enthalpy and free energy changes ranges from –47 to –294 J K–1 mol–1. The stability constants determined for the monofluoride complexes fall within the range of reported values, but those for the difluoride complexes are much higher than the fewer values that are found in literature. Lanthanon trifluorides were found to be least soluble in water at pH 3–4.

27 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
202316
202229
202141
202055
201949
201857