AP Chemistry · Summary

Unit 5 summary

1. Orders come from experiment: compare two trials where only one concentration changes, and (rate ratio) = (concentration ratio)^order.
2. The units of k make the rate come out in M/s: s⁻¹ for first order, M⁻¹ s⁻¹ for second order overall, M⁻² s⁻¹ for third.
3. Straight-line plots: [A] against t for zero order, ln[A] against t for first order, 1/[A] against t for second order.
4. Only a first-order reaction has a constant half-life, $t_{1/2} = 0.693/k$.
5. An elementary step's rate law follows its coefficients; the slow step sets the predicted rate law, with intermediates replaced.
6. Intermediates are made then used; catalysts are used then remade. Neither appears in the overall equation.
7. Higher temperature raises the fraction of collisions with energy at least Ea; a catalyst lowers Ea and leaves ΔH unchanged.