4.3 Representations of Reactions

Before-and-after drawings must conserve atoms. Use them to find limiting reactant: whatever runs out first.

Leftover particles in the 'after' picture are excess reactant.

Count atoms by type in both boxes; they must match.

Worked example: 4 H₂ + 3 O₂ drawn → 4 H₂O formed, 1 O₂ left over. H₂ limits.