Types of Chemical Reactions

Thousands of known chemical reactions occur. We can classify reactions according to various similarities. General information about types of chemical reactions can be used to predict the products of specific reactions. We are going to classify reactions according to five basic types

Synthesis Decomposition Single-displacement Double-displacement Combustion

Synthesis Reactions A + X  AX Two or more substances combine to form a new compound

Types of Synthesis Reactions A metal + O2  a metal oxide A metal + S8  a metal sulfide A nonmetal + O2  nonmetal oxide A metal + a halogen  a halide Active metal oxide + water  metal hydroxide Nonmetal oxide + water  oxyacid

Decomposition Reactions AX  A + X A single compound undergoes a reaction that produces two or more simpler substances

The decomposition of a substance by running an electric current through it is called electrolysis. This is how water is decomposed into hydrogen and oxygen gases.

Types of Decomposition Reactions Oxides of less-active metals decompose into their elements Metal carbonates decompose when heated to produce a metal oxide + CO2 Metal hydroxides decompose when heated to form metal oxide + water Metal chlorates decompose when heated to form a metal chloride + O2 Some acids decompose into nonmetal oxides + water

Single-Displacement Reactions A + BX  AX + B or Y + BX  BY + X One element replaces a similar element in a compound. A metal displaces a metal A halogen displaces a halogen A metal can displace hydrogen or vice versa Often takes place in aqueous solution.

Types of Single Displacement Reactions A metal in a compound can be displaced by another metal One hydrogen in water can be displaced by an active metal The hydrogen in an acid can be displaced by an active metal The halogen in a compound can be displaced by another halogen

Single displacement reactions can only take place when the single element is MORE reactive than the element it is replacing in the compound

Double Displacement Reactions AX + BY  AY + BX The ions of two compounds exchange places in aqueous solution to form two new compounds. One of the compounds formed is usually a precipitate, an insoluble gas, or a molecular compound (like water).

Types of Double-Displacement Reactions Precipitate Formation One of the compounds produced is insoluble in water and so precipitates out of the solution Gas Formation One of the compounds produced is an insoluble gas that bubbles out of the solution. Water formation One of the compounds produced is water Remember that H+ + OH- = H2O

Combustion Reactions A substance combines with oxygen The reaction produces a large amount of energy in the form of light and heat The combustion of hydrocarbons produces CO2 and H2O CxHy + O2  CO2 + H2O