Decomposition potential of water

This determines the value of the reversible decomposition potential of water if hydrogen escapes into the atmosphere at a pressure of pHa and oxygen at a pressure of pQi. If both gases escape at the pressure pa2 = p0j = 1 atm., then the theoretical decomposition potential of water at 25 °C is ... 

A negative means that the process does not occur spontaneously it can be made to occur only by applying an external voltage sufficient to overcome the intrinsic negative voltage of the cell. In the electrolysis of water, this minimum external voltage, which is called the decomposition potential of water, is 1.229 V. When this potential difference has been applied, an... 

Fig. 7.1 Position of band edges and photodecomposition Fermi energies levels of various non-oxide semiconductors. E(e,d) represents decomposition energy level by electrons, while E(h,d) represents the decomposition energy level for holes vs normal hydrogen electrode (NHE). E(VB) denotes the valence band edge, E(CB) denotes the conduction band edge. E(H2/H20) denotes the reduction potential of water, and (H2O/O2) the oxidation potential of water, both with reference to NHE.

The reversible electrical potential (AG/nF = to split the 0-H bond in water is 1.229 V. In addition, heat is needed for the operation of an electrolysis cell. If the heat energy is supplied in the form of electrical energy, then the thermal potential is 0.252 V (at standard conditions), and this voltage must be added to Ej (i.e., add entropic term TAS to AG). The (theoretical) decomposition potential for water at standard conditions (for AH = AH°) is then 1.480 V. This is shown in figure 2.1. Anode and cathode reactions for electrolysis (see figure 2.1) are ... 

Potential Fire Hazard from Anaerobic Decomposition in Cooling Water System, Safety Note No. DOE/EH-0109, U.S. Dept, of Energy, Washington, D.C., Oct. 1989. 

Notwithstanding their very low vapor pressure, their good thermal stability (for thermal decomposition temperatures of several ionic liquids, see [11, 12]) and their wide operating range, the key property of ionic liquids is the potential to tune their physical and chemical properties by variation of the nature of the anions and cations. An illustration of their versatility is given by their exceptional solubility characteristics, which make them good candidates for multiphasic reactions (see Section 5.3.4). Their miscibility with water, for example, depends not only on the hydrophobicity of the cation, but also on the nature of the anion and on the temperature. 

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