Chemistry: Chemical Reactions

Chemical Reactions

The standard representation of a chemical reaction shows an arrow pointing from the reactants to the products:

Typically, solids are labeled (s), liquids (l), and gases (g). The numerical coefficients in front of the chemical formulas express the moles of each compound or element. The preceding reaction can be interpreted in terms of moles or weights. (See Table 1 .)

TABLE 1

Interpretation of a Reaction

*Quantity*	*Fe₂O₃*	CO	Fe	*CO₂*
Moles	1	3	2	3
Weight of 1 mole	159.70	28.01	55.85	44.01
Total weights	159.70	84.03	111.70	132.03

Notice that the total weight of the reactants (243.73 g) equal the total weight of the products. This demonstrates the law of conservation of mass, which applies to all chemical reactions.

It is not true, however, that volumes must be conserved in reactions involving gases. The complete combustion of carbon monoxide is a case in point:

Because the reaction coefficients are proportional to relative volumes of each gas, 2 volumes of carbon monoxide and 1 volume of oxygen (a total of 3 volumes of reactants) combine to produce only 2 volumes of carbon dioxide. In gaseous reactions, the total volume of the products may be less than, or equal to, or greater than the total volume of the reactants.