Reading and understanding
Read an equation as a statement
Reactants are written to the left of the arrow and products to its right. A plus sign separates different substances. The arrow communicates a proposed or known chemical change under the stated conditions; it is not a claim that the change must occur instantaneously or safely at home. Chemists can add notes above arrows about catalysts, temperature and other conditions. An equation is a compact model, not a complete experiment report.
Multiply coefficients, preserve formulas
The formula H₂O represents one water molecule with two hydrogen atoms and one oxygen atom. The symbol 2H₂O represents two such molecules, for a total of four hydrogen and two oxygen atoms. A subscript lives inside the molecular formula and changes the substance when altered. Changing H₂O into H₂O₂ represents hydrogen peroxide, not 'fixed' water. When balancing an equation, change coefficients, never the underlying formulas.
What an atom ledger tells us
In 2H₂ + O₂ → 2H₂O, the left contains four hydrogen atoms and two oxygen atoms; the right contains the same. There are three molecules on the left, but two on the right. This is not an error: the number of molecules does not have to match. It is the number of atoms of each element that must be the same. This difference is one of the most important habits for balancing equations.
Describe physical states honestly
The suffix (s) means solid, (l) liquid, (g) gas, and (aq) aqueous, or dissolved in water. These annotations communicate experimental context, but a formula alone cannot reveal reaction rate, final yield, or whether substances actually react. Even a perfectly balanced written equation can represent conditions that are not feasible in practice. Use equations for conservation bookkeeping and investigate reaction evidence separately.