réactions

Réactions is the plural form of the French noun réaction, and is used in both French and English to denote responses to stimuli or processes that transform substances. In science, the term encompasses chemical reactions, biochemical reactions, and physical responses; in everyday language it also refers to emotional or behavioral responses to events or information.

In chemistry, a chemical reaction describes the transformation of reactants into products through changes in chemical bonds. Reactions are represented by balanced equations that conserve atoms, and their rates depend on factors such as concentration, temperature, pressure, and the presence of catalysts. Thermodynamics determines whether a reaction is energetically favorable, while kinetics describes the speed of the process. Many reactions are reversible and reach an equilibrium where forward and reverse processes occur at equal rates.

In biology and medicine, reactions include enzymatic transformations in metabolism, cellular signaling, and immune responses. Reaction times indicate how quickly a system responds to a stimulus, from reflexes to complex behavioral changes. In pharmacology, adverse drug reactions are unintended, potentially harmful responses to medications that require monitoring and management.

In social and cultural contexts, reactions describe how individuals or groups respond to news, policies, art, or events. These reactions can be emotional, cognitive, or behavioral and may influence opinions, markets, or social dynamics. Studies in psychology, sociology, and communication analyze the drivers and consequences of collective reactions and the feedback loops they create.

Measurement and modeling of reactions involve kinetics, thermodynamics, and mechanism studies, with methods ranging from spectroscopy and calorimetry to observational and sociological approaches.