What Does Chemical Stability Mean?
Chemical stability, when used in the technical sense, means thermodynamic stability of a chemical system. In corrosion, it is the ability to resist corrosion under specific environmental conditions. It is the tendency of a material to resist change or decomposition due to internal reaction, or due to the action of air, heat, light, pressure, etc.
More noble metals are chemically more stable than other metal. Therefore, they are more corrosion resistant.
Corrosionpedia Explains Chemical Stability
Chemical stability is the resistance to attachment by chemical action. In materials science, a chemical substance is said to be stable if it is not particularly reactive in the environment or during normal use, and retains its useful properties on the timescale of its expected usefulness. In particular, the usefulness is retained in the presence of air, moisture or heat, and under the expected conditions of application. In this meaning, the material is said to be unstable if it can corrode, decompose, polymerize, burn or explode under the conditions of anticipated use or normal environmental conditions.
For example, advanced ceramics are highly resistant to chemical corrosion due to their high levels of chemical stability. Corrosion-resistant ceramics possess low chemical solubility and therefore have particularly high resistance to chemical corrosion.
Thermodynamic stability occurs when a system is in its lowest energy state, or chemical equilibrium, with its environment. This type of chemical thermodynamic equilibrium persists indefinitely unless the system is changed. Chemical systems might include changes in the phase of matter or a set of chemical reactions.
Chemical substances or states can persist indefinitely even though they are not in their lowest energy state if they experience metastability, a state which is stable only if not disturbed too much. A substance (or state) might also be termed "kinetically persistent" if it is changing relatively slowly. Metastable and kinetically persistent species or systems are not considered truly stable in chemistry.
Chemically stable materials are less reactive and thereby more corrosion resistant.