Reakcija

Reakcija is a term used in several languages to denote a process by which substances or systems change in response to interaction, yielding new substances, states, or effects. In science, the concept spans chemistry, biology, physics, and social contexts. Reactions are often described by changes in energy, composition, or structure, and may be reversible or irreversible.

In chemistry, a chemical reaction involves reactants transforming into products through breaking and forming chemical bonds. Reactions are described by stoichiometry and kinetics, may release or absorb energy, and are often accelerated by catalysts. Common types include redox reactions, acid-base neutralizations, precipitation reactions, and polymerizations. Examples: methane combustion: CH4 + 2 O2 → CO2 + 2 H2O; acid-base neutralization: HCl + NaOH → NaCl + H2O; photosynthesis: 6 CO2 + 6 H2O → C6H12O6 + 6 O2.

In biology, reactions include metabolic reactions catalyzed by enzymes, such as glycolysis, digestion, and signal transduction. Enzymes lower activation energy and provide specificity and regulation; reactions can be catabolic or anabolic. In immunology, immune reactions describe responses to pathogens.

In physics and everyday life, reaction denotes the response of a system to a force (reaction force). In social contexts, people exhibit reactions to events, information, or policies, which can be measured by behavior or opinion.