Reactivity

Reactivity is the tendency of a substance to undergo chemical change. It encompasses the likelihood of reacting with other substances, with energy input such as heat or light, or both. Reactivity results from the interplay of thermodynamics—whether a reaction is energetically favorable—and kinetics—how fast it proceeds under given conditions.

Key factors include electronic structure, temperature, pressure, concentration, surface area, and the presence of a catalyst. The rate of a reaction is described by its rate law and rate constant, which typically increase with temperature according to the Arrhenius equation. Activation energy is the minimum energy required to reach the transition state; substances with lower activation energies react more readily at a given temperature.

Reactivity varies across the periodic table. Alkali metals and alkaline earth metals are highly reactive with water and air, halogens are highly reactive and strong oxidizers, while noble gases are generally inert. Metals are often assessed by a reactivity series, which ranks them by their tendency to lose electrons, while nonmetals are considered in terms of their tendency to gain electrons or engage in covalent bonding. Standard electrode potentials quantify a species’ tendency to be reduced; more positive potentials indicate greater oxidizing strength.

Understanding reactivity informs synthesis, materials science, and safety. It guides the selection of reactants, conditions, and catalysts to control product formation, as well as risk assessment for handling reactive substances, such as water-reactive or pyrophoric materials.