Word & Chemical Equations

Balancing via Coefficients: To balance an equation, you must add whole numbers called coefficients in front of the chemical formulas. These numbers multiply the entire molecule or atom count.

The 'Trial and Error' Approach: Systematically adjust coefficients from left to right, checking the atom counts for each element on both sides until they are equal.

Isolating Elements: It is often most effective to balance elements that appear on their own (like $O_2$ or $Mg$) last, as changing their coefficient will not affect other elements in the equation.

State Symbols: Always include the physical state of the substances using standard notation: (s) for solid, (l) for liquid, (g) for gas, and (aq) for aqueous solutions.

The Final Audit: Always perform a final count of every element on both sides after you believe the equation is balanced; a single missing atom can invalidate the entire equation.

Diatomic Awareness: Remember that certain elements must be written as diatomic molecules when they are alone: $H_2, N_2, O_2, F_2, Cl_2, Br_2, I_2$.

Identifying Products: In word-based exam questions, look for keywords like 'to form', 'produces', or 'are formed when' to distinguish between reactants and products.

Checking Ratios: Ensure your coefficients are in the simplest whole-number ratio possible (e.g., use $1:2:1$ instead of $2:4:2$).

Altering Subscripts: NEVER change the small subscript numbers in a chemical formula to balance an equation. Changing $H_2O$ to $H_2O_2$ changes the chemical identity from water to hydrogen peroxide.

Ignoring State Symbols: Students often forget to include (aq) for substances in solution, which is critical for accurately describing the environment of the reaction.

Incomplete Burning: When a question mentions 'burning in air', it implies a reaction with oxygen gas ($O_2$), which must be included as a reactant.