OXIDATIOX-REDUCTION TOTENTIALS 21 



each atom carried is handed over to the oxygen atom to 

 help it complete its stable octet of electrons. Thus the 

 oxidation of hydrogen means the loss of electrons to 

 oxygen. It will be seen that oxidation of ferrous to 

 ferric chloride also involves loss of an electron from the 

 iron to a chlorine atom. The same thing applies to all 

 oxidations : in every case the oxidised atom loses one or 

 more electrons to some other atom or atoms. It has 

 become evident that every oxidation (or loss of electrons) 

 must necessarily be associated with a gain of those 

 electrons by the other partner in the reactions, that is, 

 every oxidation is accompanied by an equivalent reduction 

 (which is a gain in electrons), and conversely every 

 reduction must have its counterpart in a simultaneous 

 oxidation. The one reaction cannot occur without the 

 other. 



This transfer of electrons, which is the inevitable 

 accompaniment of all oxidation - reduction reactions, 

 affords a means whereby the process may be measured by 

 electrical means, since a transfer of the charged electron 

 alters the electrical state of the parts of the system or, 

 in other words, sets up a potential difference between the 

 reactants. The magnitude of this potential difference 

 depends on the ease with which the electrons are lost or 

 gained, the greater the tendency for a movement of 

 electrons (that is, the greater oxidising or reducing power 

 of a substance) the greater will be the potential on one or 

 other side of zero. The more highly oxidised a substance 

 is (that is, the more ready it is to take up electrons) the 

 more positive will be its potential, and the more highly 

 reduced a substance is (that is, the more ready it is to 

 part with electrons) the more negative will be the potential. 



Here, too, as in all other reversible reactions, the 

 Law of Mass Action applies, and in general for the 

 reaction : — 



Reductant ;==^ Oxidant + ne 



(where " e " represents an electron and " n " the number of 



