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Physical Factors in Phase Formation
Published in Daniel D. Pollock, PHYSICAL PROPERTIES of MATERIALS for ENGINEERS 2ND EDITION, 2020
The E-B correlation postulates that the allotropic form with the highest energy of sublimation is the most probable because it represents the most stable (greatest bond strength) configuration. The prediction of the BCC lattice is complicated by an entropy effect. Because this crystal type is not close-packed, comparatively large ionic vibrational amplitudes can occur. As the temperature increases, the entropy increases, causing a decrease in Gibbs free energy. Where lattice types appear to show approximately equal bond strengths, the lowering of the free energy can impart a higher probability for the presence of the BCC rather than the HCP or FCC lattices.
Electrochemistry and Electroanalytical Techniques
Published in Ashutosh Kumar Dubey, Amartya Mukhopadhyay, Bikramjit Basu, Interdisciplinary Engineering Sciences, 2020
Ashutosh Kumar Dubey, Amartya Mukhopadhyay, Bikramjit Basu
Gibbs free energy is a manifestation of the internal energy that is available for a system to perform certain work under the given conditions of constant pressure (and preferably, temperature also). When a spontaneous process is performed by the system, its free energy decreases. Hence, for a system involving chemical reactions, the change in Gibbs free energy signifies whether the reaction is thermodynamically favorable (for −ve ΔG) or not (for +ve ΔG). Now, if a system performs some other work (wext), in addition to the basic PΔV, then Equation (6.3) can be re-written as ΔU=TΔS−PΔV−wext
2 Utilization via Dry Reforming of Methane
Published in Subhas K Sikdar, Frank Princiotta, Advances in Carbon Management Technologies, 2020
Mohamed S Challiwala, Shaik Afzal, Hanif A Choudhury, Debalina Sengupta, Mahmoud M El-Halwagi, Nimir O Elbashir
Reforming reactions generally take place at high temperature and pressure conditions, typically in the range of 900–1100 °C and 15–25 bar, in order to achieve the maximum allowable equilibrium conversion. The equilibrium composition of gas phase reaction is estimated via the Gibbs free energy minimization method. Gibbs free energy (or the chemical potential of the system) is the total free energy available in the system to do useful or external work, and is a function of temperature, pressure and composition of the system.
Ultrasonic characterisation of the binary mixture of 2,3-dichloroaniline with methanol and ethanol
Published in Indian Chemical Engineer, 2022
Mahendra Kumar, Mohd Aftab Khan, Chandreshvar Prasad Yadav, Dharmendra Kumar Pandey, Dhananjay Singh
Compressibility/ultrasonic velocity enhances/decays with an increase in mole fraction of solvent, while viscosity decays. Therefore, both parameters jointly influence the mole fraction-dependent variation of thermal relaxation time, while viscosity is a governing factor towards the relative thermal relaxation time for both types of binary mixtures. The relative value of thermal relaxation time for both types of binary mixtures reveals that binary mixture 2,3-DCA+ methanol shall have better stability with a strong bonding through the relaxation process than binary mixture 2,3-DCA + ethanol. Pico-second order of thermal relaxation time defines the occurrence of the structural relaxation process within mixtures. This confirms that molecules are rearranged in the binary mixture with hydrogen bonding and dipole interaction through an accommodating process [33,34]. Gibbs free energy is the sum of Helmholtz energy and regular work done at constant temperature and pressure. On mixing two equilibrium state liquids to form a binary system, maximum work is done by the decay in Helmholtz energy. Hence, Gibbs free energy of binary system measures maximum work done contributed to form the binary system from constituent liquids in equilibrium condition through the relaxation process.
A comparative DFT study of structural, electronic, thermodynamic, optical, and magnetic properties of TM (Ir, Pt, and Au) doped in small Tin (Sn5 & Sn6) clusters
Published in Phase Transitions, 2022
Aoly Ur Rahman, Dewan Mohammad Saaduzzaman, Syed Mahedi Hasan, Md. Kabir Uddin Sikder
In this study, we’ve investigated the changes of Gibbs free energy (ΔG), enthalpy (ΔH), entropy (ΔS) to get a better understanding of the thermodynamic properties. These thermodynamic properties for LanL2DZ are tabulated in Table 2 and for SDD basis sets are in ST 3. Gibbs free energy is the parameter that measures the maximum reversible work done at constant temperature and pressure in any reversible system. The positive value of Gibbs free energy (ΔG) indicates the non-spontaneous process whereas the negative value of ΔG indicates the spontaneous process, and zero for equilibrium [41]. From Table 2, it has been found that the negative value for the clusters of Gibbs free energy gradually increases with the increase of the atomic number of the dopant which indicates that the greater the atomic number of dopants more spontaneous the cluster. A similar phenomenon has been shown for the increase in the number of Sn atoms in Table 2. The Sn6 system is more spontaneous than the Sn5. In Figure 3(a), a comparative graphical representation of Gibbs free energy of Sn5 and Sn6 systems has been shown.
Prediction of product gas composition from biomass gasification by the method of Gibbs free energy minimization
Published in Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, 2021
Ruta Khonde, Shubham Hedaoo, Samir Deshmukh
Gasification of waste biomass can serve as a means of treating waste because of its various advantages and environment friendliness. Present attempt is for development of a model which can predict the equilibrium gas composition. At equilibrium the system has minimum value of Gibbs free energy. The Gibbs free energy minimization method provides an efficient way to predict the equilibrium concentration of the products formed. The formation of CO, CO2, H2, CH4, Tar (C10H8), H2S, and N2 are considered along with unconverted carbon. The optimization is performed with the help of Solver Tool of MS-Excel spreadsheet, which uses gradient reduction as well as Lagrangian multiplier method for the calculation of minimum value of Gibbs free energy. The assumption of carbon conversion is an important factor. The results with complete carbon conversion show a very large deviation from the literature value of hydrogen and methane which are the main constituents of the syngas. It means that complete carbon conversion could not be assumed while modeling. However, when incomplete carbon conversion was considered, the values predicted by the model for all the gaseous products, closely matches with the values from the literature (Guan et al. 2009).