One beaker (right) contains redox couple A with an equimolar mixture of the reduced (Ared) and oxidized (Aox) members of its redox couple.                   NAD+  +  2H+  +  2e-    <--->   NADH  +  H+    The other beaker contains the hydrogen reference standard ( H2 <-->2H+ + 2e-), whose redox potential is arbitrarily set to ZERO by international agreement. A salt bridge is formed from a concentrated KCl solution allowing the ions K+ & Cl- to move between the two beakers to neutralize the charges between them. The metal wire (red) provides a resistance-free path for electrons, and a voltmeter measures the redox potential of substance A.    If electrons move from Ared to H+, as shown, the redox couple has a negative redox potential. If they flow from H2 to Aox, this couple has a positive redox potential.      thus, theremodynamically e-'s flow from...      more  electronegative to more electropositive