The driving force for transport of a component in salinity gradient power is a gradient in Gibbs energy or a potential difference between the two salt solutions. The Gibbs energy of a system reflects that part of the energy of the system that is available for work. The total amount of energy available from mixing 1m of a concentrated and 1m of a diluted salt solution can be determined from the chemical potential difference of the system after mixing, subtracted by the chemical potential of the system before mixing (Fig. 1):
where AGmix is the change in Gibbs energy (J/mol) and Gb, Gc, and Gd are the Gibbs energies of the brackish, the concentrated, and the diluted solution, respectively (J/mol). The Gibbs energy of an ideal solution is equal to g = mn (2)
where G is the Gibbs energy of the system (J/mol), m the chemical potential of component i in the solution (J/mol), and ni the number of moles of component i in the solution.
The chemical potential of a component i (m) in an ideal solution can be written as (e.g., )
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