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State Le Châtelier’s principle - Leaving Cert Chemistry - Question b - 2006
Question b
State Le Châtelier’s principle. The following equilibrium is set up in solution by dissolving cobalt(II) chloride crystals in water to form the pink species Co(H₂O)... show full transcript
Worked Solution & Example Answer:State Le Châtelier’s principle - Leaving Cert Chemistry - Question b - 2006
Step 1
Step 2
When the solution becomes blue, has reaction ceased? Explain.
Answer
No, the forward and reverse reactions continue at the same rate, meaning that reactants are still converting into products and vice versa. The blue colour indicates a shift in the equilibrium position, but it does not imply that the reaction has stopped.
Step 3
State and explain the colour change observed on cooling the reaction mixture.
Answer
When the reaction mixture is cooled, the colour changes from blue to pink. This occurs because the forward reaction is endothermic, meaning it absorbs heat. Cooling decreases the temperature, causing the equilibrium to shift to the left to produce heat, favoring the formation of the pink Co(H₂O)₆²⁺ species.
Step 4
Other than heating, mention one way of reversing the change caused by cooling the reaction mixture.
Answer
One way to reverse the change is to add concentrated hydrochloric acid (HCl), which increases the concentration of chloride ions (Cl⁻) in the system. This addition shifts the equilibrium to the right, leading to the formation of blue CoCl₄²⁻.