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Thermodynamic and Kinetic Control

Favorability and speed are different questions. A reaction's thermodynamic favorability is set by ΔG, but its rate is set by the activation-energy barrier (kinetics). So a strongly favored reaction (negative ΔG) can be extremely slow — diamond turning to graphite is favored but takes ages.

UNIT 9 TOPIC 9.4 • THERMODYNAMIC AND KINETIC CONTROL THERMO VS KINETIC ΔG predicts thermodynamic favorability, not rate — not how fast a reaction actually goes. A reaction can be thermodynamically favored (ΔG < 0) yet still slow when Eₐ is large. Reaction-coordinate diagram free energy, G reactants transition state products Eₐ ΔG < 0 reaction progress → Products lie below reactants (ΔG < 0) — yet the reaction must climb Eₐ first. THERMODYNAMICALLY FAVORED ΔG < 0 → reaction is spontaneous Tells you the reaction CAN happen and where equilibrium lies. Says nothing about how fast. KINETIC CONTROL (Eₐ) A large activation energy Eₐ makes the reaction SLOW — regardless of ΔG. Rate depends on Eₐ and temperature, not on ΔG. EXAMPLE: diamond → graphite C(diamond) → C(graphite) ΔG < 0 : graphite is more stable (thermodynamically favored). But Eₐ is enormous, so diamond persists for ages — favored, yet unreactive. BOTTOM LINE ΔG sets the destination; Eₐ sets the speed. Thermodynamically favored ≠ fast. AP Chemistry · Unit 9 · Applications of Thermodynamics
Favorability and speed are separate. A thermodynamically favored reaction (negative ΔG) can still be extremely slow, because rate depends on the activation-energy barrier, not on ΔG. A slow, stalled reaction is not the same as one at equilibrium.
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The traps conflate favorability with rate (a favored reaction need not be fast, and a slow one need not be unfavorable) and confuse a kinetically stalled system with equilibrium — a reaction frozen by a high barrier is far from equilibrium, and a catalyst speeds it without changing ΔG.

The work

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Lesson
Thermo vs Kinetic Control ›

ΔG sets favorability, activation energy sets rate — so a favored reaction can be slow. The lesson separates the two and handles catalysts and stalls, then closes with a ten-scenario check.

Skill check · 10 scenarios
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Diagnostic
10-item topic check ›

Ten items spanning the Topic 9.4 misconceptions: favorability conflated with rate, and a kinetically stalled reaction confused with equilibrium (and the catalyst's role).

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Targeted Practice
Drill a single misconception ›

Pick one of the failure modes you missed and drill it on its own. The round is adaptive: two correct in a row clears the misconception and moves you to the next.

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