1. Every reaction answers two independent questions: how fast, and how far.
Rate (kinetics) and position (equilibrium) are set by different quantities, so a reaction can be favorable yet slow, or fast yet unfavorable.
tert-Butyl bromide hydrolyzes to tert-butanol — this SN1 is both slow and downhill.
2. Kinetics is governed by the activation energy of the highest transition state.
The larger the energy barrier Ea the slower the reaction, and catalysts or more stable transition states lower that barrier.
Ionization to the tert-butyl carbocation is the tall, slow, rate-determining step.
3. The slow step is rate-determining, and its stability decides the rate.
Because SN1 rate depends on carbocation formation, a more stable cation means a lower barrier and a faster reaction.
The secondary isopropyl cation is less stable than tertiary, so this ionizes more slowly.
4. Equilibrium is governed by the relative stabilities of reactants and products.
A negative ΔG (exergonic) means products are more stable than reactants, so a large Keq pushes the reaction toward product.
Trapping the cation with water gives stable tert-butanol — a downhill, product-favored step.
5. Acid-base equilibria always favor the side with the weaker acid.
Proton transfer sits toward the more stable, lower-energy conjugate base, so the weaker acid dominates at equilibrium.
Acetic acid gives resonance-stabilized acetate — its stability sets the equilibrium position.
6. Summary
Kinetics = how fast, set by Ea · Slow step is rate-determining · Equilibrium = how far, set by ΔG / Keq · Stability decides position · Favorable can still be slow.
Quiz yourself
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The activation energy Ea of the highest transition step — a bigger barrier means a slower reaction.
ΔG (or Keq), set by the relative stabilities of reactants and products; a negative ΔG favors products.
Ionization to the cation is the slow, rate-determining step, so a more stable cation lowers Ea and speeds the reaction.
Yes — a negative ΔG only guarantees a favorable position, not speed; a high barrier can leave it kinetically trapped.
Draw this on the whiteboard
Open the OChem Board whiteboard — benzene rings, wedge/dash bonds, and a clickable periodic table built in. No account needed.