?CHEMICAL EQUATIONSDOE-HDBK-1015/1-93Fundamentals of ChemistryCH-01Rev. 0Page 44The equation weight in grams of a compound or element is defined as the gram molecular weighttimes the number of molecules of the compound, as shown by the coefficients of the chemicalequation for the reaction. The sums of the equation weights on each side of a chemical equationmust be equal. Chemical calculations are based on the fact that every fraction or multiple of theequation weights of substances that react gives a corresponding fraction or multiple of theequation weights of the products of the reaction. In other words, if 30 grams of a substance thathas an equation weight of 15 grams reacts with some amount of another substance to form aproduct with an equation weight of 20 grams, then 40 grams of that product will be formed.Example:How many grams of ferric oxide will be formed if 27.9 grams of iron reacts with wateraccording to the following equation.Solution:The equation weight of iron equals the gram atomic weight of iron times the number ofatoms shown reacting in the equation, which is two. Using Table 2:Because 27.9 g of iron react, the fraction of the equation weight that reacts is:.Thus, 1/4 of the equation weight of ferric oxide will be formed.The equation weight of ferric oxide equals the gram molecular weight of ferric oxidetimes the number of molecules shown formed in the equation, which is one.Using Table 2:Thus, the amount of ferric oxide formed is:.
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