Affinity
Definition and meaning of Affinity in chemistry.
Affinity is the natural tendency of atoms or substances to combine with each other to form new compounds. It measures the strength of attraction between chemical species.
In more detail
Chemical affinity drives chemical reactions and is fundamentally related to electronegativity and bond energy. Substances with high affinity for each other will react readily. The stronger the affinity between elements, the more thermodynamically stable the resulting compound will be. Understanding affinity helps predict which elements bond preferentially with others and explains why certain compounds form spontaneously.
Key facts
| Field | General Chemistry |
|---|---|
| Measurement | Quantified using Gibbs free energy change (ΔG) and thermodynamic properties |
| Relationship | Closely related to electronegativity, ionization energy, and electron affinity |
| Periodic trend | Elements in the same group often exhibit similar affinities for common partners |
Oxygen has high affinity for hydrogen, which is why water (H2O) forms readily and is extremely stable. This strong affinity between hydrogen and oxygen drives their combination and produces a molecule with very strong covalent bonds.
Frequently asked questions
How is chemical affinity different from electronegativity?
Affinity describes the tendency of one atom or substance to combine with another, while electronegativity measures an individual atom's ability to pull electrons toward itself within a bond.
Can affinity be negative or zero?
Affinity is fundamentally expressed as a Gibbs free energy change (ΔG); negative ΔG values indicate spontaneous, thermodynamically favorable reactions, while positive values indicate non-spontaneous reactions. A reaction can be endothermic yet still favorable if entropy changes are sufficiently positive.