Composition Stoichiometry refers to the examination of the relative abundances of elements within chemical compounds. In order to use composition stoichiometry to calculate the desired quantitative data, it is important to understand the relationships between the elements in chemical compounds. This requires knowing how the atoms are bonded, and by extension its chemical formula.
For example, methane (CH4) has one central carbon with covalent bonds to four hydrogen atoms with each bond separated by 109.5 degrees in three dimensional space. So considering composition stoichiometry, the molar ratio of carbon to hydrogen would be 1:4. Thus, if there were four moles of carbon in a sample of methane, then it can be calculated using composition stoichiometry that there would be 16 moles of hydrogen.
However, since carbon is twelve times heavier than hydrogen, the mass ratio is 12:4, or more simply, 3:1. Thus, if there were 0.12 grams of carbon in a sample of methane, then based on the mass ratio, it can be calculated that there would be 0.04 grams of hydrogen.
Therefore, understanding the relationships between elements within compounds is absolutely fundamental for compositional stoichiometric calculations.