types of reactionsWhen we delve deeper into the study of chemistry, we find that there are several different types of reactions. There are several different ways to classify these reactions, mainly based on the patterns of similarity among them. There are 5 basic types of reactions we will be studying, and the way they are classified is based on how atoms or groups of atoms are rearranged during a particular reaction. These reactions are:
the 5 basic types of reactions
combination reactionsA combination reaction is a reaction in which two substances combine to form a third substance. A simple example would be where two elements react to form a compound of the elements. A good example of this would be:
combination reaction where two elements react to form a compound of the elements
Combination reactions can also have compounds as the reactants. An example of this would be where phosphorus trichloride reacts with chlorine to form phosphorus pentachloride:
combination reactions with compounds as the reactants
Here is another combination reaction, the burning of copper and oxygen to produce copper(II) oxide:
another example of a combination reaction
Decomposition ReactionsA decomposition reaction is a reaction in which a single compound reacts to give two or more substances. In order to decompose a compound, it is often necessary to raise the temperature. An example of a decomposition reaction would be the decomposition of mercury (II) oxide into mercury and oxygen when the compound is heated.
A compound can also decompose into a compound and an element, or two compounds.
displacement reactionsDisplacement reactions (sometimes referred to as single replacement reactions) are reactions in which an element reacts with a compound displacing an element from it. An example of this would be when a copper metal strip is dipped into a solution of silver nitrate. When this happens, crystals of silver metal are produced.
Cu(s) + 2AgNO3 (aq) -> 2Ag (s) + Cu(NO3)2 (aq)In this reaction, copper replaces the silver in silver nitrate. In the process it produces copper(II) nitrate solution and silver metal. A fun fun single replacement reaction is one that we call "burning magnesium".
2Mg + CO2 -> 2MgO + C
metathesis reactionsA metathesis reaction is a reaction that appears to involve the exchange of parts of the reactants. Metathesis reactions are also referred to as double-replacement reactions. When the reactants in the reaction are ionic compounds in solution, cations and anions of the compounds are the parts exchanged. An example of a metathesis reaction would be the reaction of potassium iodide solution and lead (II) nitrate solution. The reactants are colorless liquids, yet one of the products of this reaction is lead (II) iodide, which forms a yellow precipitate. A precipitate is a solid compound formed during a reaction in solution.
2KI(aq) + Pb(NO3)2(aq) -> 2KNO3(aq) + PbI2(s)What happens in this metathesis reaction is that iodide ions in potassium iodide switch with the nitrate ions in lead (II) nitrate. What happens is that we get potassium nitrate (2KNO3) and lead (II) iodide (PbI2) as the products.Here is another example of a double replacement reaction in which iron(III) chloride and sodium hydroxide are combined to produce a precipitate:
FeCl3 + 3NaOH -> 3NaCl + Fe(OH)3
So far, all the reactions which we have studied have been classified by the type of atom rearrangement that happens in the reaction. Combustion reactions are different in that they are characterized by the fact that one of the reactants is always oxygen. A combustion reaction is a reaction of a substance with oxygen, usually with the rapid release of heat to produce a flame. Organic compounds burn in oxygen to produce carbon dioxide and water vapor. Here is the formula for the chemical reaction involving butane burning in air to produce carbon dioxide and water vapor.
2C4H10(g) + 13O2(g) -> 8CO2(g) + 10H2O(g)
Here is an example of a combustion reaction. It involves burning methane. This results in carbon dioxide and water being formed from the reaction:
CH4 + 2O2 -> CO2 + 2H2O