Consider the following equilibrium system - HSC - SSCE Chemistry - Question 23 - 2024 - Paper 1

The mixture becomes more blue as temperature is increased, indicating an increase in the concentration of the blue complex ion $[CoCl_4]^{2-}$. This suggests that the forward reaction is favored at higher temperatures, leading to a shift in equilibrium towards products.

Thus, as temperature rises, the equilibrium shifts right, boosting the concentration of $[CoCl_4]^{2-}$ at the expense of $[Co(H_2O)_6]^{2+}$ and $Cl^-$ ions. In accordance with Le Chatelier's principle, the increase in temperature shifts the equilibrium position to favor the endothermic direction, which, in this case, is the formation of $[CoCl_4]^{2-}$.

This shift results in a larger value of the equilibrium constant $K_{eq}$, defined as:

$K_{eq} = \frac{[[CoCl_4]^{2-}]}{[[Co(H_2O)_6]^{2+}]\cdot [Cl^-]^4}$

Thus, the increase in temperature not only alters the color but also influences the equilibrium constant $K_{eq}$.