By Grahame Turner | Updated Aug 30, 2022
A chemical formula is a concise, standardized representation of a chemical reaction. While they may seem intimidating at first, understanding the logic behind each component makes them straightforward.
Start with the written reaction. Look for key words such as “burned,” “reacts with,” or “yields.” For example, if the text says “methane (CH4) is burned,” you know the reactants are CH4 and O2 (oxygen). The products will follow the word “yields.”
List each species in its chemical formula: CH4, O2, CO2, H2O. The word “yields” indicates the transformation, so place reactants on the left side of the arrow and products on the right.
Replace narrative verbs with symbols: “yields” becomes →, and separate each species with a plus sign (+). Think of each formula as a distinct molecule. For a burning reaction, you typically need additional O2 to match the stoichiometry.
Apply the Law of Conservation of Mass: atoms that enter the reaction must leave in equal numbers. Count the atoms of each element on both sides. For methane combustion: CH4 + O2 → CO2 + H2O You’ll find four hydrogen atoms on the left but only two in H2O on the right. Place a 2 in front of H2O so that each CH4 produces two water molecules.
After balancing hydrogen, check oxygen. The reaction now has four oxygen atoms in the products but only two in the single O2 molecule on the left. Place a 2 before O2 to supply the needed atoms: CH4 + 2 O2 → CO2 + 2 H2O This fully balanced equation now satisfies the conservation principle.
Confirm that each element’s count is identical on both sides. Remember, a chemical equation cannot create or destroy atoms; it only rearranges them.
Chemical equations are typically expressed in moles, but balancing can be visualized with individual molecules. A mole equals 6.0221415 × 1023 entities—use this as a reference when checking stoichiometry.
