Mendeleev · Science

Equilibrium constant: reading K without a false story

The equilibrium constant describes a ratio of species activities at equilibrium for a given reaction and temperature. A large K favors products at equilibrium but does not mean the reaction is fast.

Understand before calculating

The equilibrium constant describes a ratio of species activities at equilibrium for a given reaction and temperature. A large K favors products at equilibrium but does not mean the reaction is fast.

Example

A reaction can have a very large K yet remain slow when its activation barrier is high: thermodynamics and kinetics answer different questions.

The classic trap

Do not turn a model into a literal photograph of reality. Scientific models select particular properties to explain or predict a phenomenon; knowing their limits is part of using them correctly.

Understanding check

Explain the concept to someone who knows the periodic table but not this chapter. Then give one example and one situation where the most common shortcut would become misleading.

A reaction can have a very large K yet remain slow when its activation barrier is high: thermodynamics and kinetics answer different questions.