Balancing Chemical Equations

Core Formulas

In a balanced equation, the number of atoms of each element is equal on both sides.

Coefficients a, b, c, d are the smallest whole numbers that balance all elements.

Only coefficients may be changed — never subscripts.

Atom Balance

How To Use

Pick a reaction preset. Use the + and − buttons to adjust each coefficient. The atom balance panel shows real-time counts for each element on both sides. When all elements match, the equation turns green and you earn a ✓. Try all 8 reactions, from simple synthesis to combustion and redox.

Concept

Chemical equations represent reactions where atoms rearrange but are never created or destroyed (Law of Conservation of Mass, Lavoisier 1789). Balancing means finding the smallest set of integer coefficients so that every element has equal atom counts on both sides.

A balanced equation is the foundation of stoichiometry — it tells you the mole ratios needed for quantitative calculations such as yields, limiting reagents, and percent composition.

Balancing Strategy

Balance metals first, then nonmetals, then hydrogen, and oxygen last. For combustion reactions, balance C first, then H, then O. Redox reactions may require half-reaction balancing.

Why It Matters

Every AP Chemistry calculation (stoichiometry, limiting reagent, gas laws) depends on a balanced equation. It is the single most tested skill in AP Chem FRQs.

Keyboard Shortcuts

Space Animate · R Reset · 1–8 Presets · Q Quiz · H Hint

Live Data

Reaction—

Total LHS atoms—

Total RHS atoms—

Status—

Presets

Speed 1.00×