Stoichiometry: Chemical Formulas and Equations

Patterns of chemical reactivity

We can often predict a reaction if we have seen a similar reaction before. For example, sodium (Na) reacts with water (H₂0) to form sodium hydroxide (NaOH) and H₂ gas:

Potassium (K) is in the same family (column) of elements in the periodic table. Therefore, one might predict that the reaction of K with H₂O would be similar to that of Na:

In fact, all alkali metals react with water to form their hydroxide compounds and hydrogen.

Combustion reactions are rapid reactions that produce a flame. Most common combustion reactions involve oxygen (O₂) from the air as a reactant. A common class of compounds which can participate in combustion reactions are hydrocarbons (compounds that contain only carbon and hydrogen).

When hydrocarbons are combusted they react with oxygen (O2) to form carbon dioxide (CO₂) and water (H₂O). For example, when propane is burned the reaction is:

Other compounds which contain carbon, hydrogen and oxygen (e.g. the alcohol methanol CH₃OH, and the sugar glucose C₆H₁₂O₆) also combust in the presence of oxygen (O₂) to produce CO₂ and H₂O.

In combination reactions two or more compounds react to form one product:

In decomposition reactions one substance undergoes a reaction to form two or more products. For example, many metal carbonates undergo a heat dependent decomposition to the corresponding oxide plus CO₂: