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Chemistry · Glossary

What is Shift of an equilibrium?

Definition 4.11 University Chemistry — Year 2 · Chapter 4 — Equilibrium Constants and Shifts

When a system at equilibrium is perturbed (a change of temperature, of pressure, or of an amount), it is no longer at equilibrium in general and evolves to a new one. The shift of the equilibrium is forward if the reaction advances ( ⁣dξ>0\dd\xi > 0) and backward otherwise.

A perturbation moves Q (or K, if the temperature changes); the system then shifts until Q = K again, forward if Q has become too small, backward if too large.
A perturbation moves QQ (or K∘K^\circ, if the temperature changes); the system then shifts until Q=K∘Q = K^\circ again, forward if QQ has become too small, backward if too large.
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