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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 Gibbs free energy of kornelite, paracoquimbite, Fe 2 (SO 4 ) 3 ·5H 2 O, and Fe 2(SO 4 ), as a function of temperature and relative humidity of air is calculated.
Abstract: Enthalpies of formation of kornelite [Fe 2 (SO 4 ) 3 ·~7.75H 2 O] and paracoquimbite [Fe 2 (SO 4 ) 3 ·9H 2 O] were measured by acid (5 N HCl) solution calorimetry at T = 298.15 K. The samples were characterized chemically by an electron microprobe, and structurally by the means of single-crystal, in-house powder, and synchrotron powder X-ray diffraction. The refined structures for the two phases are provided, including estimates of the positions and concentration of non-stoichiometric water in structural channels of kornelite, location of the hydrogen atoms and the hydrogen bonding system in this phase. The measured enthalpies of formation from the elements (crystalline Fe, orthorhombic S, ideal gases O 2 and H 2 ) at T = 298.15 K are −4916.2 ± 4.2 kJ/mol for kornelite and −5295.4 ± 4.2 kJ/mol for paracoquimbite. We have used several algorithms to estimate the standard entropy of the two phases. Afterward, we calculated their Gibbs free energy of formation and constructed a phase diagram for kornelite, paracoquimbite, Fe 2 (SO 4 ) 3 ·5H 2 O, and Fe 2 (SO 4 ) 3 as a function of temperature and relative humidity of air. The topology of the phase diagram is very sensitive to the entropy estimates and the construction of a reliable phase diagram must await better constraints on entropy or Gibbs free energy of formation. Possible remedies of these problems are also discussed.

26 citations

Journal ArticleDOI
TL;DR: In this article, oil palm leaf powders were used as new non-conventional and low-cost adsorbents for the removal of copper (II) ions from aqueous solution.
Abstract: Oil palm leaf powders (OPLP), an agricultural waste material, were used as new non-conventional and low-cost adsorbents for the removal of copper (II) ions from aqueous solution. Batch studies were performed to evaluate and optimize the effects of various parameters such as contact time, pH of the solution, initial metal ion concentrations and adsorbent dosage. Langmuir, Freundlich and Temkin isotherms were used to analyze the equilibrium data at different temperatures. The experimental data fit well with the Langmuir adsorption isotherm, indicating thereby the mono layer adsorption of the copper (II) ions. The monolayer sorption capacity of OPLP for copper (II) ions was found to be 11.22 mg/g at 30 ◦C. The thermodynamic parameters like standard free energy, standard enthalpy, and standard entropy changes for the adsorption of copper (II) ions have also been computed and discussed. The heat of adsorption [∆H◦ = -39.84 kJ/mol] implied that the adsorption was exothermic in nature.

26 citations

Journal ArticleDOI
TL;DR: In this article, light scattering was used to establish the dependence of the critical micelle temperature, CMT, on concentration for solutions of three polystyrene-block-poly(ethylene/propylene) copolymers in decane.
Abstract: Light scattering was used to establish the dependence of the critical micelle temperature, CMT, on concentration for solutions of three polystyrene-block-poly(ethylene/propylene) copolymers in decane. Electron microscopy studies of particles isolated from the solutions showed that the micelles had narrow size distributions and micellization could be treated thermodynamically as a closed association. The light scattering results were used to calculate the standard Gibbs energies of micellization, ΔGφ, and the standard enthalpy, ΔHφ, and entropy contributions, —TΔSφ. The values of ΔHφ were large and negative, and markedly dependent on the molecular weight of the polystyrene block. The values of ΔGφ for the three samples were on the other hand very similar to each other. The standard entropy contributions were unfavourable to micelle formation.

26 citations

Journal ArticleDOI
TL;DR: In this paper, the heat capacity of a synthetic two-line ferrihydrite, which showed typically broad X-ray diffraction peaks due to small particle size and/or disorder but had a rather low excess water content, FeOOH·0.027H2O, was measured over the temperature range of (2 to 300) K. The fit required an anisotropic ferrimagnetic spin wave component.

26 citations

Journal ArticleDOI
TL;DR: In this paper, the heat capacity of synthetic, stoichiometric wadeite-type K2Si4O9 has been measured by DSC in the 195≤T(K)≤598 range.
Abstract: The heat capacity of synthetic, stoichiometric wadeite-type K2Si4O9 has been measured by DSC in the 195≤T(K)≤598 range. Near the upper temperature limit of our data, the heat capacity observed by DSC agrees with that reported by Geisinger et al. (1987) based on a vibrational model of their infrared and Raman spectroscopic data. However, with decreasing temperature, the Cp observed by DSC is progressively higher than that predicted from the vibrational model, suggesting that the standard entropy of K2Si4O9 is likely to be larger than 198.9 ± 4.0 J/K · mol computed from the spectroscopic data. A fit to the DSC data gave: Cp(T) = 499.13 (±1.87) − 4.35014 · 103(±3.489 · 101) · T −0.5, with T in K and average absolute percent deviation of 0.37%. The room-temperature compressibilities of kalsilite and leucite, hitherto unknown, have been measured as well. The data, fitted to the Murnaghan equation of state, gave K o = 58.6 GPa, K o ′ = 0.1 for kalsilite and K o = 45 GPa, K o ′ = 5.7 for α-leucite. Apart from the above mentioned data on the properties of the individual phases, we have also obtained reaction-reversals on four equilibria in the system K2O-Al2O3-SiO2. The Bayesian method has been used simultaneously to process the properties of 13 phases and 15 reactions between them to derive an internally consistent thermodynamic dataset for the K2O-Al2O3-SiO2 ternary. The enthalpy of formation of K2Si4O9 wadeite is in perfect agreement with its revised calorimetric value, the standard entropy is 232.1 ± 10.4 J/K · mol, ∼15% higher than that implied by vibrational modeling. The phase diagram, generated from our internally consistent thermodynamic dataset, shows that for all probable P-T trajectories in the subduction regime, the stable pressure-induced decomposition of K-feldspar will produce coesite + kalsilite rather than coesite + kyanite + K2Si4O9 (cf. Urakawa et al. 1994).

26 citations


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