Reactions & Stoichiometry

Matter is neither created nor destroyed in a chemical reaction, so total mass of reactants equals total mass of products. This is why equations must be balanced.

Adjust stoichiometric coefficients (never subscripts) so each element has equal atom counts on both sides, satisfying conservation of mass.

The number placed before a formula in a balanced equation; it gives the mole ratio in which substances react and form.

The SI unit for amount of substance: one mole contains Avogadro's number of entities. It links the atomic scale to measurable masses.

6.022 × 10²³ — the number of particles (atoms, molecules, ions) in exactly one mole of a substance.

The mass of one mole of a substance in grams, numerically equal to the formula mass in amu. Found by summing the molar masses of all atoms in the formula.