4 Enthalpy and entropy of fusion

AbstractThis paper presents the corrosion and inhibition behavior of heat-treated EN8 dual-phase steel with ferrite-martensite structure with pectin in 0.5 M sulphuric acid. The corrosion studies were performed using the weight loss method, electrochemical techniques such as potentiodynamic polarization measurements, and impedance spectroscopy. The study was done at different concentrations of pectin in the temperature range of 40 to 70 °C and immersion time of 1, 3, 5, and 7 h. The results showed that the inhibition performance of pectin has enhanced with an increase in pectin concentration and decreased with the temperature and time of exposure. From the weight loss study, highest inhibition efficiency of 76.43% was achieved at 5.0 g/L at 1 h of exposure at 40 °C. The maximum inhibition efficiency of 62% was obtained with 5.0 g/L of pectin at 40 °C by potentiodynamic polarization method. The energy, enthalpy, and entropy of activation and also thermodynamic parameters like free energy, enthalpy, and entropy of adsorption were assessed and discussed. Appropriate adsorption isotherm was fit to the obtained experimental outcomes and achieved Langmuir adsorption isotherm to be the best fit and obeyed physical adsorption. Surface analysis: scanning electron microscopy, X-ray diffraction techniques, atomic force microscopy, and energy dispersive X-ray were done with and without the addition of pectin. The metal surface appears to be uniform and smooth in the presence of pectin and adsorption was confirmed by surface analysis.

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The crystallization enthalpy and entropy of protein solutions: microcalorimetry, van't Hoff determination and linearized Poisson–Boltzmann model of tetragonal lysozyme crystals

Physical Chemistry Chemical Physics ◽

10.1039/d0cp06113a ◽

2021 ◽

Vol 23 (4) ◽

pp. 2686-2696

Author(s):

Lorena Hentschel ◽

Jan Hansen ◽

Stefan U. Egelhaaf ◽

Florian Platten

Keyword(s):

Theoretical Description ◽

Protein Solutions ◽

Consistent Picture ◽

Poisson Boltzmann ◽

Enthalpy And Entropy ◽

Boltzmann Model ◽

Lysozyme Crystals ◽

Solution Parameters

Microcalorimetric and van't Hoff determinations as well as a theoretical description provide a consistent picture of the crystallization enthalpy and entropy of protein solutions and their dependence on physicochemical solution parameters.

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A Rational Equation of State for Water and Water Vapor in the Critical Region

Journal of Heat Transfer ◽

10.1115/1.3688683 ◽

1964 ◽

Vol 86 (3) ◽

pp. 320-326 ◽

Cited By ~ 1

Author(s):

E. S. Nowak

Keyword(s):

Water Vapor ◽

Equation Of State ◽

Thermodynamic Properties ◽

Specific Heat ◽

Critical Point ◽

Critical Region ◽

Constant Pressure ◽

Parametric Equation ◽

Enthalpy And Entropy ◽

Specific Volumes

A parametric equation of state was derived for water and water vapor in the critical region from experimental P-V-T data. It is valid in that part of the critical region encompassed by pressures from 3000 to 4000 psia, specific volumes from 0.0400 to 0.1100 ft3/lb, and temperatures from 698 to 752 deg F. The equation of state satisfies all of the known conditions at the critical point. It also satisfies the conditions along certain of the boundaries which probably separate “supercritical liquid” from “supercritical vapor.” The equation of state, though quite simple in form, is probably superior to any equation heretofore derived for water and water vapor in the critical region. Specifically, the deviations between the measured and computed values of pressure in the large majority of the cases were within three parts in one thousand. This coincides approximately with the overall uncertainty in P-V-T measurements. In view of these factors, the author recommends that the equation be used to derive values for such thermodynamic properties as specific heat at constant pressure, enthalpy, and entropy in the critical region.

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