Ligand substitution reactions

Question 1

Why does ligand substitution occur?

Answer 1

• other ligands form stronger co-ordinate bonds
• or they are present in higher conc and the equilibrium is displaced
• decrease in coordination number

Question 2

What is the ovarall equation of the ligand substituion by ammonia in excess?

Answer 2

• [M(H₂O)6]²⁺ + 6NH₃ ⇌ [M(NH₃)₆]²⁺ + 6H₂O

Question 3

Why does ammonia replace water

Answer 3

• ammonia is a better ligand
• higher conc of ammonia displaced the equilbria to the right
  
  • thus displacing water and OH-
• needs large excess

Question 4

Why does precipitate dissolve in water?

Answer 4

• ligand substitution occur
• hexaqua ion conc falls
• precipitate dissolves and eqm moves to left in that reaction

Question 5

How does chloride act as a ligand

Answer 5

in HCl

replaces water

increase in coordination number and entropy

Question 6

Suggest why enthalpy change for ligan d subsitituion is zero of 1-2diaminoethane and [Cu(NH₃)6]²⁺?

Answer 6

• Cu - N bonds formed similar enthalpy to Cu-N bonds broken
• same number of bonds broken and made