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Reaction Equilibrium
Published in R. Ravi, Chemical Engineering Thermodynamics, 2020
The standard state is open to choice and the choice is dictated by the availability of tables [2–4] that contain the so called standard Gibbs free energy of formation and the standard enthalpy of formation of various species at 298.15 K. Using the data in the tables, one may calculate the standard Gibbs free energy change due to reaction and the activity based equilibrium constant at 298.15 K. These concepts are introduced in section 6.2.3. In section 6.2.4, the temperature dependence of the equilibrium constant is studied and an expression for calculating the equilibrium constant at any temperature is derived. In section 6.2.5 the ideas in the preceding sections are brought together to obtain the defining equation for calculating the equilibrium extent of reaction and hence the composition of the reaction mixture at equilibrium. Various other equilibrium constants are introduced in the process. Specialized expressions, valid when the reaction mixture may be approximated as an ideal gas mixture, are derived. In section 6.2.6, the various rules that are part of the Le Chatelier’s principle are rigorously derived for an ideal gas mixture. Finally, examples which illustrate some of the ideas introduced above are presented.
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
where, ΔGfi0 = Standard Gibbs free energy of formation for the component ‘i’R = universal gas constant (Pa×m3mol×K)
2 Structure, Thermodynamics, and Kinetics
Published in Yun Zheng, Bo Yu, Jianchen Wang, Jiujun Zhang, Carbon Dioxide Reduction through Advanced Conversion and Utilization Technologies, 2019
Yun Zheng, Bo Yu, Jianchen Wang, Jiujun Zhang
CO2 is one of the most common final products in any combustion reaction, including chemical or biological.7 CO2 conversion is difficult from a thermodynamic standpoint. Figure 2.4 shows the standard Gibbs free-energy of formation (“B” represents one of the reactants or products in the reaction, “f” represents the “formation”, and the “θ” indicates the standard state of 298.15 K and 101.325 kPa) of C1 species with different oxidation states of carbon. In terms of thermodynamics, it indicates that the CO2 conversion reaction tends to be endergonic when the O/C ratio of one product is less than 27. On the contrary, the reaction tends to be exergonic when CO2 is kept in its +4 oxidation state with various O/C ratios in the products (such as carbonates or urea). In regard to specific conversion reactions as listed in Table 2.1, the Gibbs free energy change (ΔG) of these conversion reactions from CO2 to other products as shown under a standard state is positive (ΔGθ > 0), showing that the conversion reactions are non-spontaneous. Additionally, with respect to the standard enthalpy changes (ΔHθ > 0) of various products listed in Table 2.1, the ΔHθ values of all these conversion reactions are also positive, demonstrating that these CO2 conversion processes are endothermic under a standard state.
In-situ VN reinforced powder metallurgy M30 steels prepared from water atomized powers via pressureless sintering
Published in Powder Metallurgy, 2020
Haixia Sun, Fang Yang, Qian Qin, Biao Zhang, Alex A. Volinsky, Zhimeng Guo
In this paper, in-situ VN reinforced PM HSS was prepared by pressureless sintering under the nitrogen atmosphere. Among commonly used pressureless sintering processes, nitrogen sintering was widely employed in the preparation of metal and ceramic parts [18–20]. As opposed to the common pressureless sintering process via adding graphite to balance the carbon content, this study was designed to decrease the carbon content in the V-containing HSS. Despite that, the PM HSS with VN strengthening possessed excellent performance. The carbon effects and sintering behaviour in the PM HSS were studied. Besides, the microstructure, elemental distribution and phase composition of the VN reinforced phase were investigated. Accordingly, the hardness, bend strength and impact energy were measured. Based on the analysis of phase formation energy and standard Gibbs free energy, the formation mechanism of carbides and nitrides in the HSS was also clarified.
Molybdenum-99 from Molten Salt Reactor as a Source of Technetium-99m for Nuclear Medicine: Past, Current, and Future of Molybdenum-99
Published in Nuclear Technology, 2023
Jisue Moon, Kristian Myhre, Hunter Andrews, Joanna McFarlane
A significant amount of molybdenum in a MSR remains as a metal deposit on reactor surfaces. Additionally, molybdenum is not stable as a fluoride species at the redox potentials in the MSRE salt. A comparison of each metal species was presented by Guo et al. in Ref. 66. A species with a higher reduction potential possesses a higher tendency to acquire electrons and be reduced. If a standard F2/F− electrode is selected as the reference, the standard electropotential of reaction can be calculated by the standard Gibbs free energy of formation of MFn through the following equation:
Evolving new group contribution-LSSVM model to estimate standard molar chemical exergy of pure organic substances
Published in Petroleum Science and Technology, 2018
Mahdi Mir, Majid Kamyab, Milad Janghorban Lariche, Razieh Razavi, Alireza Baghban
Standard molar chemical exergy is expressed by the following equation based on appropriate formation Gibbs energy equation and chemical exergy values of the constituent elements of the compounds while considering the reversible reaction for formation of the chemical compounds: where ΔG°f, nj, and ϵ°j stand for standard Gibbs free energy of formation, number of jth constituent element atoms, and the jth constituent elements standard molar chemical exergy, respectively.