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...
|
|