Chemical Reactions

Condensation Reaction

A condensation reaction is one in which two molecules combine to form a larger molecule, with the loss of a small molecule. The small molecule lost is usually water, but not always. It can be considered to be the opposite of hydrolysis reactions, and is an important reaction in the manufacture of many polymers. Example: CH3NH2 + CH3COOH → CH3NHCOCH3 + H2O

Decomposition Reaction

A decomposition reaction involves the breaking down of a chemical compound into elements or simpler compounds. It is sometimes defined as the opposite of a synthesis reaction. They can occur spontaneously, or be initiated by heat, a catalyst, or electrolysis. An example is the decomposition of hydrogen peroxide into hydrogen and oxygen. Example: 2H2O2 → 2H2O + O2

Displacement Reaction

A displacement reaction is when an element or ion moves out of one compound and into another. It usually occurs if the element moving into the compound is more reactive than the element it displaces. Double displacement reactions also occur, where anions and cations of two different molecules swap places, forming two different compounds. Example: Mg + 2H2O → Mg(OH)2 + H2

Hydrolysis Reactions

A hydrolysis reaction involves the breaking of chemical bonds by the addition of water to a substance. In some cases, this addition can cause both the substance and the water molecule to split into two parts. There are three main types of hydrolysis: salt, acid, and base. Dissolving sulfuric acid in water is a simple example of hydrolysis. Example: H2SO4 + H2O → H3O+ + HSO4-

Neutralization Reaction

A neutralisation reaction is one in which an acid and a base react to form a salt. Water is commonly produced as well. Often these reactions are exothermic, but endothermic neutralisations are possible. Neutralisation reactions do not necessarily result in a pH of 7 - resultant pH is dependent on the strength of the acid and the base. Example: NaOH + HCl → NaCl + H2O

Precipitation Reaction

A precipitation reaction is one in which aqueous compounds react to form an insoluble solid, called a precipitate. This solid can be suspended throughout the solution, or fall to the bottom of the reaction vessel. Whether or not the product of a reaction will form a precipitate is determined by solubility rules for ionic compounds. Example: 2NaOH(aq) +MgCl2(aq) → 2NaCl(aq) + Mg(OH)2(s)

Addition/Synthesis Reaction

Addition reactions, also known as synthesis reactions or direct combination reactions, involve two or more reactants combining to form a single, more complex product. Examples are the reaction of iron and sulfur to form iron sulfide, or, in organic chemistry, the reaction of ethene and bromine to form dibromoethane. Example: C2H4 + Br2 → C2H4Br2

Combustion Reaction

Combustion reactions involve oxygen reacting with another element or compound to produce energy in the form of heat & light. They are always exothermic. Complete combustion requires a plentiful supply of oxygen - in a limited supply, incomplete combustion occurs, and different products can be formed. When organic chemicals combust completely, the products always include carbon dioxide and water. Example: CH4 + 2O2 → 2H2O + CO2

Oxidation Reaction

Oxidation reactions are sometimes defined as reactions in which other elements 'gain', or form bonds with, oxygen atoms. More generally, they can be defined as reactions in which atoms of an element lose electrons. Oxidation does not occur without an accompanying reduction reaction - these reactions are known as redox reactions. Example: 4Fe + 3O2 + 2H2O → 2Fe2O3.H2O

Reduction Reaction

Reduction reactions are sometimes defined as chemical reactions in which other elements 'lose' oxygen atoms. More generally, they can be defined as reactions in which atoms of an element gain electrons. Reduction does not occur without an accompanying oxidation reaction - these reactions are known as redox reactions. Example: Fe2O3 + 3CO → 2Fe + 3CO2