Elements and compounds interact in many ways. Remembering each type of chemical reaction is challenging and unnecessary because almost every inorganic chemical reaction can be divided into one or more of four categories.
Combination Reactions
In this chemical reaction, two or more reactants form a chemical product. An example of a binding reaction is the formation of sulfur dioxide when sulfur is burned in the air:
S (s) + O2 (g) → SO2 (g)
Decomposition Reactions
In a decomposition reaction, a compound is decomposed into two or more chemical substances. Decomposition is usually the result of electrolysis or heating. An example of a decomposition reaction is the decomposition of mercury oxide into its constituent chemical elements.
2HgO (s) + heat → 2Hg (l) + O2 (g)
Single Displacement Reactions
A single substitution reaction is characterized by the substitution of an atom or ion of a single compound for an atom of another element. An example of a single displacement reaction is that zinc metal displaces copper ions in copper sulfate solution to form zinc sulfate:
Zn (s) + CuSO4 (aq) → Cu (s) + ZnSO4 (aq)
Single displacement reactions are usually subdivided into more specific categories (e.g., redox reactions).
Double Displacement Reactions
Double display reactions can also be referred to as metathesis reactions. In this reaction, the elements of the two compounds are replaced with each other to form a new compound. A double displacement reaction may occur when a product is removed from the solution as gas or sediment, or when the two substances combine to form an undivided weak electrolyte in the solution. An example of a double displacement reaction occurs in the solution of calcium chloride and silver nitrate to form insoluble silver chloride in the solution of calcium nitrate.
CaCl2 (aq) + 2 AgNO3 (aq) → Ca(NO3)2 (aq) + 2 AgCl (s)
A neutralization reaction is a special type of double displacement reaction, which occurs when an acid reacts with alkali to solve salt and water. An example of neutralization reaction is the reaction of hydrochloric acid and sodium hydroxide to produce sodium chloride and water:
HCl (aq) + NaOH (aq) → NaCl (aq) + H2O (l)
Remember, reactions can fall into more than one category. In addition, more specific categories may be proposed, such as combustion reaction or precipitation reaction. Learning the main categories will help you balance equations and predict the types of compounds formed by chemical reactions.
