Chemical stability
Encyclopedia
Chemical stability when used in the technical sense in chemistry
, means thermodynamic stability of a chemical system.
Thermodynamic stability occurs when a system is in its lowest energy state, or chemical equilibrium
with its environment. This may be a dynamic equilibrium
, where individual atoms or molecules change form, but their overall number in a particular form is conserved. This type of chemical thermodynamic equilibrium will persist indefinitely unless the system is changed. Chemical systems might include changes in the phase of matter or a set of chemical reaction
s.
State A is said to be more thermodynamically stable than state B if the Gibbs energy of the change from A to B is positive.
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 (and thus is not at thermodynamic equilibrium, but is observed anyway). Metastable and kinetically persistent species or systems are not considered truly stable in chemistry. Therefore, the term chemically stable should not used in chemistry as a synonym of unreactive because it confuses thermodynamic and kinetic concepts. On the other hand, highly chemically unstable species tend to undergo exothermic unimolar decompositions at high rates. Thus, high chemical instability may sometimes parallel unimolar decompositions at high rates.
, 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.
Chemistry
Chemistry is the science of matter, especially its chemical reactions, but also its composition, structure and properties. Chemistry is concerned with atoms and their interactions with other atoms, and particularly with the properties of chemical bonds....
, means thermodynamic stability of a chemical system.
Thermodynamic stability occurs when a system is in its lowest energy state, or chemical equilibrium
Chemical equilibrium
In a chemical reaction, chemical equilibrium is the state in which the concentrations of the reactants and products have not yet changed with time. It occurs only in reversible reactions, and not in irreversible reactions. Usually, this state results when the forward reaction proceeds at the same...
with its environment. This may be a dynamic equilibrium
Dynamic equilibrium
A dynamic equilibrium exists once a reversible reaction ceases to change its ratio of reactants/products, but substances move between the chemicals at an equal rate, meaning there is no net change. It is a particular example of a system in a steady state...
, where individual atoms or molecules change form, but their overall number in a particular form is conserved. This type of chemical thermodynamic equilibrium will persist indefinitely unless the system is changed. Chemical systems might include changes in the phase of matter or a set of chemical reaction
Chemical reaction
A chemical reaction is a process that leads to the transformation of one set of chemical substances to another. Chemical reactions can be either spontaneous, requiring no input of energy, or non-spontaneous, typically following the input of some type of energy, such as heat, light or electricity...
s.
State A is said to be more thermodynamically stable than state B if the Gibbs energy of the change from A to B is positive.
Chemical stability versus reactivity
Thermodynamic stability applies to a particular system. The reactivity of a chemical substance is a description of how it might react across a variety of potential chemical systems and, for a given system, how fast such a reaction could proceed.Chemical substances or states can persist indefinitely even though they are not in their lowest energy state if they experience metastability
Metastability
Metastability describes the extended duration of certain equilibria acquired by complex systems when leaving their most stable state after an external action....
- 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 (and thus is not at thermodynamic equilibrium, but is observed anyway). Metastable and kinetically persistent species or systems are not considered truly stable in chemistry. Therefore, the term chemically stable should not used in chemistry as a synonym of unreactive because it confuses thermodynamic and kinetic concepts. On the other hand, highly chemically unstable species tend to undergo exothermic unimolar decompositions at high rates. Thus, high chemical instability may sometimes parallel unimolar decompositions at high rates.
Outside chemistry
In everyday language, and often in materials scienceMaterials science
Materials science is an interdisciplinary field applying the properties of matter to various areas of science and engineering. This scientific field investigates the relationship between the structure of materials at atomic or molecular scales and their macroscopic properties. It incorporates...
, 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.