Chemistry · Equations & quantities

Balancing Equations.

In a reaction, atoms swap partners but none appear or vanish. That one rule explains why mass is conserved, why equations must balance, and why one reactant can run out before the other.

Check you've got it

Key words

Reactants · productsThe substances you start with · the new substances that form. They go on the left and right of the arrow

Conservation of massAtoms are rearranged, never created or destroyed, so the total mass stays the same. A mass change on an open balance means a gas left or joined

SubscriptThe small number after a symbol or bracket. It counts atoms inside the formula. Changing it changes the substance

CoefficientThe big number in front of a formula. It multiplies the whole formula, and it's the only number you change to balance an equation

Balanced equationThe same number of each type of atom on both sides, using the smallest whole-number coefficients

Limiting reactantThe reactant that runs out first. It decides how much product can form; the other reactant is left over

Where this leads: the atoms themselves are in Inside an Atom; balanced combustion equations are in the Bunsen Burner Lab; metals reacting with acids, water and oxygen are in the Metal Reactions Lab.

Narration voice: Max, generated with ElevenLabs.