A redox reaction be used as a source of electrical energy only when two half-reactions are physically separated. <span>The electrons that are released at the anode flow through the wire, producing an electric current. Galvanic cells therefore transform chemical energy into electrical energy that can then be used to do work.</span>
Electrical energy is the energy produced due to flow of electrons.
Whereas a reaction in which oxidation and reduction reaction takes place is known as a redox reaction. Basically, there is exchange of electrons that take place in a redox reaction.
For example,
Oxidation half reaction:
Reduction half reaction:
Hence, this flow of electrons acts as a source of electrical energy.
The boiling points need to differ by 50 degrees to enable their complete separation ie of two different liquids. The separation occurs by first evaporation of one of the liquids and then its condensation and collection. It is a physical process not a chemical one.