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Since all the input energy for such processes is heat, they can be more efficient than high-temperature electrolysis. This is because the efficiency of electricity production is inherently limited. Thermochemical production of hydrogen using chemical energy from coal or natural gas is generally not considered, because the direct chemical path ...
Water splitting can be done at higher pH values as well however the standard potentials will vary according to the Nernst equation and therefore shift by -59 mV for each pH unit increase. However, the total cell potential (difference between oxidation and reduction half cell potentials) will remain 1.23 V.
Photocatalysts must conform to several key principles in order to be considered effective at water splitting. A key principle is that H 2 and O 2 evolution should occur in a stoichiometric 2:1 ratio; significant deviation could be due to a flaw in the experimental setup and/or a side reaction, neither of which indicate a reliable photocatalyst for water splitting.
The thermodynamic standard cell potential can be obtained from standard-state free energy calculations to find ΔG° and then using the equation: ΔG°= −n F E° (where E° is the cell potential and F the Faraday constant, 96,485 C/mol). For two water molecules electrolysed and hence two hydrogen molecules formed, n = 4, and
In thermochemistry, a thermochemical equation is a balanced chemical equation that represents the energy changes from a system to its surroundings. One such equation involves the enthalpy change, which is denoted with Δ H {\displaystyle \Delta H} In variable form, a thermochemical equation would appear similar to the following:
First-order phase transitions exhibit a discontinuity in the first derivative of the free energy with respect to some thermodynamic variable. [6] The various solid/liquid/gas transitions are classified as first-order transitions because they involve a discontinuous change in density, which is the (inverse of the) first derivative of the free ...
At the interface between the phases (in the classical problem) the temperature is set to the phase change temperature. To close the mathematical system a further equation, the Stefan condition, is required. This is an energy balance which defines the position of the moving interface.
In thermodynamics, the chemical potential of a species is the energy that can be absorbed or released due to a change of the particle number of the given species, e.g. in a chemical reaction or phase transition.