Ligand Substitution Reactions
If concentrated HCl is added to a solution of hexaaquacopper (II) ions the solution turns from blue to yellow. The tetrachlorocuprate (II) complex is more stable than hexaaquacopper (II) ions. The reaction is exothermic but there is little enthalpy change because bonds are of similar strength.

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Key terms in this lesson
- ligand
- An atom, ion or molecule that donates a pair of electrons to a central metal ion to form a co-ordinate bond.
- monodentate ligand
- A ligand that can donate only one pair of electrons, forming one co-ordinate bond with the central metal ion.
- bidentate ligand
- A ligand that can donate two pairs of electrons, forming two co-ordinate bonds with the central metal ion.
- entropy
- A measure of the number of ways particles and their energy can be arranged, or the degree of disorder of a system.
More in Redox Reactions
- Shapes of complex ions
- Isomerism
- Formation of Coloured Ions
- Spectroscopy
- Vanadium
- Tollens Reagent
- Redox Potential
- Redox Titrations
All 21 lessons in Redox Reactions · All OCR A-level Chemistry topics