Longman Dictionary of Contemporary English
n. (context chemistry English) A process, typically involving the breaking or making of interatomic bonds, in which one or more substances are changed into others.
n. (chemistry) a process in which one or more substances are changed into others; "there was a chemical reaction of the lime with the ground water" [syn: reaction]
A chemical reaction is a process that leads to the transformation of one set of chemical substances to another. 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 may 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. 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.
Reactions may proceed in the forward or reverse direction until they go to completion or reach equilibrium. Reactions that proceed in the forward direction to approach equilibrium are often described as spontaneous, requiring no input of free energy to go forward. Non-spontaneous reactions require input of free energy to go forward (examples include charging a battery by applying an external electrical power source, or photosynthesis driven by absorption of electromagnetic radiation in the form of sunlight).
Different chemical reactions are used in combinations during chemical synthesis in order to obtain a 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 temperatures 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.
"Chemical Reaction'" is a song by German recording artist Sasha. It was written by Sasha, Pete Boyd Smith, Michael Kersting, and Stephan Baader for his second studio album ...You (2000), while production was overseen by the latter two. Released as the album's second single, it reached number seven in the Flemish portion of Belgium and the top forty in Austria, Germany and Switzerland.
Usage examples of "chemical reaction".
Furthermore, any change imposed on the insulin molecule by chemical reaction from without, unless the change is a rather trifling one that does not seriously affect the complexity of the molecule, produces loss of activity.
They had an instrument that expelled metal pellets at high speed by means of a controlled explosive chemical reaction.
However much the substance resulting from the chemical reaction of others might differ from these, its weight always proved to be the same as their total weight.
You can try to eliminate them with another chemical reaction, but that's going to have outputs also.
What if the compound deteriorates, and sets off a chemical reaction that causes it to explode?
There were hundreds of thousands, perhaps millions, of enzymes, each existing solely to aid a single chemical reaction.