Rate equation, order and rate constant (HL)

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**rate = k[A]^{m}[B]^{n}** — the rate equals the rate constant k times the reactant concentrations, each raised to its order.

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The **power** to which that reactant's concentration is raised in the rate equation (found by **experiment**).

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The **sum** of the individual orders (m + n).

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**Experimentally** — from how the initial rate responds to changing each concentration; **never** from the stoichiometric equation.

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**Zero order** (× 1 = 2⁰) — that reactant is not in the rate equation.

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**First order** (× 2 = 2¹).

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**Second order** (× 4 = 2²).

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The proportionality constant in the rate equation; **fixed at a given temperature** (it changes only with temperature).

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**s⁻¹** — from k = rate ÷ [A] = (mol dm⁻³ s⁻¹) ÷ (mol dm⁻³).

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**mol⁻¹ dm³ s⁻¹** — from k = rate ÷ [A]².

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**mol⁻² dm⁶ s⁻¹** — from k = rate ÷ [A]³.

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The **slowest** step in a multi-step mechanism; it sets the overall rate. The rate equation shows the species **up to and including** the RDS.