11. Conservation of Mass,       Charge, and Energy   Previous PageNext Page
       Conservation of Electrons

Mass is not the only property that is conserved in chemical reactions. In Chapter 6 we saw that, since oxidation and reduction represent only the moving of electrons away from or toward atoms, whenever something is oxidized something else must be reduced. Moving an electron away from one atom in a chemical reaction means moving it toward another one. Thus we can say that, in any chemical reaction in which oxidation and reduction take place, the net change in oxidation numbers of all of the atoms taking part is zero. Total oxidation number is conserved. This is merely an indirect way of saying that electrons are neither created nor destroyed during the reaction.

As an example, the combustion of foods during respiration in all oxygen-using forms of life requires the oxidation of carbon and hydrogen compounds. The hydrogen atoms in these compounds are assigned oxidation number zero, because each shares electrons equally with the atoms to which they are bonded. These zero-oxidation-state hydrogen atoms often are represented symbolically in brackets as , without reference to the particular source compound. The energy-yielding oxidation reaction taking place during respiration then can be written in unbalanced form as...

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