Chemical reactions and Stoichiometry
In chemistry, a chemical reaction is a process that leads to the transformation of one set of chemical substances to another set of chemical substances. In order of increasing rate, the most common types of reactions are oxidation, reduction, and hydrolysis; collectively they are known as redox reactions. The substance involved in a chemical reaction is called a reactant. In a chemical reaction, reactants are transformed into products through a series of well-defined steps. These steps are typically accompanied by a change in the chemical equilibrium of the reaction system, but may also be modified by heat (thermal reactions), light (photochemical reactions) or the presence of catalysts. In a chemical reaction, the reactant molecules often break up into several different products, but the chemical bonds between the reactant molecules are usually broken in only one step, in a process called a decomposition reaction. The products of a chemical reaction are usually not the same as the reactants. For example, in the combustion of wood, carbon dioxide and water are formed, but the original wood polymers are broken up into many different products, such as carbon, hydrogen, oxygen, and nitrogen. The breaking of chemical bonds is a fundamental aspect of all chemical reactions. Many chemical processes involve the use of chemical reagents and chemical catalysts. In general, chemical reagents are the species entering the reaction. Chemical catalysts are not consumed by the reaction, but may be converted to the product. In an industrial chemical process, catalysts are often subject to extremely harsh conditions, such as high temperatures, pressures, or chemical compounds that are highly reactive.
