Take the 2-minute tour ×  Consider a desalination process where
you enter sea water and receive fresh water and brine (or maybe
pure salt).  How do I compute the least amount of energy per
mass? I think this has something to do with the entropy of the
different mixtures, mostly dependent on the salt concentration
in the brine. Is this correct? How to calculate?  share|improve
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accepted  Assuming that the process is done at constant
temperature and pressure, what you want is the Gibbs free energy
difference. The reaction could be taken to be 1 mole of water in
brine on one side and one mole of pure water on the other side.
The result should be a positive number since the process is not
spontaneous. However the value of $\Delta G$ will be the minimum
non-mechanical work necessary for the process.  To understand
this read up on the Gibbs free energy.  share|improve this
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