Introduction

The cobalt(II) chloride equilibrium system represents a fascinating example of how chemical equilibria respond to environmental changes. This article explores the reversible reaction between hydrated and dehydrated forms of cobalt(II) chloride, a key topic in the HSC Chemistry curriculum under Factors Affecting Equilibrium.

The Equilibrium System

Cobalt(II) chloride forms a dynamic equilibrium in water between its hydrated and dehydrated forms. The hydrated complex contains six water molecules coordinated to the cobalt ion, while the dehydrated form exists as a tetrachloro complex:

$$[Co(H2O)6]^{2+}(aq) + 4Cl^-(aq) <=> [CoCl4]^{2-}(aq) + 6H2O(l)\\ \quad \Delta H > 0$$

This equilibrium system is particularly useful for demonstration purposes because:

Factors Affecting the Equilibrium

Concentration Effects

Temperature Effects

The reaction is endothermic in the forward direction (ΔH > 0):

Note: Pressure and volume changes do not affect this equilibrium as no gaseous species are involved.