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Thermodynamics of Fuel Cells
Published in Xianguo Li, Principles of Fuel Cells, 2005
If the temperature and pressure for the reactant and product mixtures are 25 °C and 1 atm (the standard reference state), the resulting enthalpy change between the product and reactant is designated as standard enthalpy of reaction. If one of the reactants involved in the reaction is a fuel and the reaction is exothermic, such a reaction is often called combustion reaction. When a combustion process is complete, that is, when a fuel (usually hydrocarbon substances) reacts completely with an oxidant (usually oxygen) to form stable final products (usually CO2 and H2O) — meaning that all of the carbon in the fuel is converted to the stable final product CO2 and all of the hydrogen in the fuel is converted to the stable final product H2O, the enthalpy change for such a combustion reaction is called enthalpy of combustion. Obviously, enthalpy of combustion depends on the initial state of the fuel and oxidant and the final state of the products (because H2O can be in liquid or vapor form with different energy content, or enthalpy values).
Basic Chemical Thermodynamics and Kinetics
Published in Kalliat T. Valsaraj, Elizabeth M. Melvin, Principles of Environmental Thermodynamics and Kinetics, 2018
Kalliat T. Valsaraj, Elizabeth M. Melvin
There are three important enthalpy terms that merit discussion. These are “standard enthalpy of reaction” (ΔHro), “standard enthalpy of formation” (ΔHfo), and “standard enthalpy of combustion” (ΔHco). The standard enthalpy of reaction is the enthalpy change for a system during a chemical reaction and is the sum of the standard enthalpy of formation of the products minus the sum of the standard enthalpy of formation of the reactants. The standard enthalpy of formation is the enthalpy change to produce 1 mol of the compound from its elements, all at standard conditions. The standards enthalpies of reaction may be combined in various ways. This is succinctly expressed in the “Hess’s law of heat summation: The standard enthalpy of a reaction is the sum of the standard enthalpies of reactions into which an overall reaction may be divided, and holds true if the referenced temperatures of each individual reaction are the same.” The standard enthalpy of combustion is that required to burn or oxidize 1 mol of the material to a final state that contains only H2O (l) and CO2.
The first law
Published in W. John Rankin, Chemical Thermodynamics, 2019
When all the substances are in their standard state, the enthalpy of reaction is called the standard enthalpy of reaction, and is written as follows: ΔrH0.
Catalytic Effect of Copper on Ozonation in Aqueous Solution
Published in Ozone: Science & Engineering, 2021
Naoyuki Kishimoto, Haruki Arai
The standard enthalpies of formation of chemical species shown in Eq. (11) are reported to be 72.1 kJ/mol for Cu+aq, 142.7 kJ/mol for O3g, −285.830 kJ/mol for H2Oliq, 65.78 kJ/mol for Cu2+aq, 0 kJ/mol for O2g, 38.95 kJ/mol for HO˙g, and −229.994 kJ/mol for OH−aq (Bard, Parsons, and Jordan 1985). Accordingly, the standard enthalpy of reaction of Eq. (11) is calculated to be −54.2 kJ, which means that Eq. (11) is an exothermic reaction. Thus, Eq. (11) is thermodynamically possible.
Catalytic Effect of Copper on Ozonation in Aqueous Solution
Published in Ozone: Science & Engineering, 2021
Naoyuki Kishimoto, Haruki Arai
The pKa of HO3˙ is reported to be 8.2 (Westerhoff et al. 1997). Thus, Equation (12) is a more efficient initiation step for HO˙ generation than the corrosion of Cu0 (Equations (5) and (6)). To the best of our knowledge, there is no report on the standard enthalpy of formation of O3˙−. Therefore, the standard enthalpy of reaction of Equation (12) is unknown. Equation (12) is composed of two electrode reactions as follows: