At low temperature the faster-forming product dominates; at high temperature the more stable one.
Practise Kinetics & Equilibrium All Kinetics & Equilibrium topics
When a reaction can give two or more products, the kinetic product is the one formed fastest because it has the lowest activation energy barrier, while the thermodynamic product is the most stable one. Under mild, irreversible conditions, typically low temperature and short reaction times, the kinetic product dominates because the faster pathway wins before equilibrium can be established. Under conditions that allow equilibration, usually higher temperature and longer times, the product distribution shifts toward the more stable thermodynamic product. The temperature and time chosen therefore control the selectivity of many organic and inorganic reactions.
Key ideas: Low temperature and short time favour the kinetic product, while high temperature and long time favour the thermodynamic one, provided the reaction is reversible. Diagnostic: warm a pure sample of the kinetic product and see whether it converts. Examples are 1,2 versus 1,4 addition to butadiene with HBr and the enolates formed from unsymmetrical ketones with strong hindered bases.
Common mistakes and connections: Students assume the more stable product always forms, or that temperature changes thermodynamic stability. Under irreversible conditions, selectivity depends on barrier heights only. Another mistake is mixing up which product is lower in energy with which has the lower barrier; they can be different species. Use reaction coordinate diagrams to compare them. Relates to the Hammond postulate and to catalysts that control selectivity.
One path has the lower barrier and gives the kinetic product fast; the other leads to a more stable product but is favoured only when heat allows equilibration. The interactive lesson shows this as a live animation or chart.
The sulfonation of naphthalene gives mainly the alpha isomer at 80 degrees C but the more stable beta isomer at 160 degrees C.
At low temperature the faster-forming product dominates; at high temperature the more stable one.
Kinetic vs Thermodynamic Product is a advanced topic in Kinetics & Equilibrium. It builds on beginner and intermediate topics, so review those first if needed.
Study these earlier topics in Kinetics & Equilibrium first: Degree of Dissociation, Relationship of Rate Constants and K, Principle of Microscopic Reversibility.
The next topics in Kinetics & Equilibrium are Hammond Postulate and Eyring Equation.
Yes. The interactive lesson includes a self-check question on Kinetic vs Thermodynamic Product, and the Kinetics & Equilibrium quiz draws on every topic in this area.
Kinetic vs Thermodynamic Product is topic 71 of 91 in Kinetics & Equilibrium.