Term: Chemical reaction
**History:**
– Antoine Lavoisier developed the theory of combustion as a chemical reaction with oxygen.
– Chemical reactions such as combustion in fire, fermentation, and the reduction of ores to metals were known since antiquity.
– Initial theories of transformation of materials were developed by Greek philosophers.
– Alchemists in the Middle Ages studied chemical transformations and attempted to convert lead into gold.
– The artificial production of chemical substances was a central goal for medieval alchemists.
**Characteristics:**
– Chemical reactions involve the rearrangement of atoms and an energy change.
– Reactants or reagents are the substances initially involved in a chemical reaction.
– Chemical reactions yield one or more products with different properties.
– Reactions often consist of a sequence of individual sub-steps.
– Reaction rates are influenced by temperature and chemical concentration.
**Types:**
– Reactions can be classified as redox or non-redox.
– Redox reactions involve oxidation and reduction.
– Most simple redox reactions fall into categories like combination, decomposition, or single displacement.
– Non-redox reactions do not involve oxidation and reduction.
– Different chemical reactions are used in chemical synthesis and biochemistry.
**Applications:**
– Chemical reactions are used in chemical synthesis to obtain desired products.
– In biochemistry, consecutive series of chemical reactions form metabolic pathways.
– Enzymes catalyze biochemical reactions, increasing reaction rates.
– Metabolic syntheses and decompositions occur in cells due to enzyme activity.
– Chemical reactions are used in various fields for practical purposes.
**Extensions:**
– The concept of chemical reactions has been extended to reactions between entities smaller than atoms.
– This includes nuclear reactions, radioactive decays, and reactions between elementary particles.
– Quantum field theory describes reactions at a fundamental level.
– Understanding reactions at a microscopic level is crucial in various scientific disciplines.
– The study of chemical reactions continues to evolve with advancements in technology and theoretical frameworks.
A chemical reaction is a process that leads to the chemical transformation of one set of chemical substances to another. When chemical reactions occur, the atoms are rearranged and the reaction is accompanied by an energy change as new products are generated. Classically, chemical reactions encompass changes that only involve the positions of electrons in the forming and breaking of chemical bonds between atoms, with no change to the nuclei (no change to the elements present), and can often be described by a chemical equation. Nuclear chemistry is a sub-discipline of chemistry that involves the chemical reactions of unstable and radioactive elements where both electronic and nuclear changes can occur.
The substance (or substances) initially involved in a chemical reaction are called reactants or reagents. Chemical reactions are usually characterized by a chemical change, and they yield one or more products, which usually have properties different from the reactants. Reactions often consist of a sequence of individual sub-steps, the so-called elementary reactions, and the information on the precise course of action is part of the reaction mechanism. Chemical reactions are described with chemical equations, which symbolically present the starting materials, end products, and sometimes intermediate products and reaction conditions.
Chemical reactions happen at a characteristic reaction rate at a given temperature and chemical concentration. Some reactions produce heat and are called exothermic reactions, while others may require heat to enable the reaction to occur, which are called endothermic reactions. Typically, reaction rates increase with increasing temperature because there is more thermal energy available to reach the activation energy necessary for breaking bonds between atoms.
A reaction may be classified as redox in which oxidation and reduction occur or non-redox in which there is no oxidation and reduction occurring. Most simple redox reactions may be classified as a combination, decomposition, or single displacement reaction.
Different chemical reactions are used during chemical synthesis in order to obtain the desired product. In biochemistry, a consecutive series of chemical reactions (where the product of one reaction is the reactant of the next reaction) form metabolic pathways. These reactions are often catalyzed by protein enzymes. Enzymes increase the rates of biochemical reactions, so that metabolic syntheses and decompositions impossible under ordinary conditions can occur at the temperature and concentrations present within a cell.
The general concept of a chemical reaction has been extended to reactions between entities smaller than atoms, including nuclear reactions, radioactive decays and reactions between elementary particles, as described by quantum field theory.