01Multi-step paths
A mechanism is a series of elementary steps that add up to the overall equation. Intermediates form in one step and are used in a later step.
A catalyst is used first and regenerated later.
02Notebook box
Intermediate: product then reactant. Catalyst: reactant then product.
Worked example: NO₂ + NO₂ → NO₃ + NO; NO₃ + CO → NO₂ + CO₂. Intermediate = NO₃.