The entropy per mole of an *n*-component ideal mixture is given by

where is the mole fraction of the *i*th constituent.
If there are only two constituents, we have

If the mixture has moles of the second constituent, we get

The energy required to separate the mixture is

For those who didn't follow the derivation, of (4), we
summarize. *R* is the universal gas constant 8.314 joules per mole
per degree Kelvin, *T* is the absolute temperature at which the
separation takes place and *x* is the mole fraction in the mixture of
the substance being extracted.

Thu Aug 21 09:12:21 PDT 1997