[化学] Types of Chemical Reactions

It is important that you know the basic types of chemical reactions forthe SAT II Chemistry test since the test often refers to reactions asbeing of one type or another. Here’s a list of the different types ofreactions, with examples of each type included.
    Synthesis reaction: This is areaction in which two or more elements or compounds combine to form asingle product. This type of reaction follows the general equation

A + BC

    where A and B may be either elements or compounds.

    Here are some examples:

2Na(s) + Cl2(g)2NaCl(s)

MgO(s) + H2O(l)Mg(OH)2(aq)

SO2(g) + H2O(l)H2SO3(aq)

    Decomposition reaction: Inthis type of reaction, a single reactant, a compound, breaks into twoor more parts. Often these are the most difficult to predict. Here isthe general equation:

ABA + B

    where A and B may be either elements or compounds.

    Here are some examples of decomposition reactions:

2H2O(l)2H2(g) + O2(g)

H2CO3(aq)H2O(l) + CO2(g)

CaCO3(s)CaO(s) + CO2(g)

2KClO3(s)2KCl(s) + 3O2(g)

    Single replacement or displacement reaction: In this type of reaction, a more active element replaces a less active element in a compound. Among the halogens, F2is the most active halogen, and the activity of the halogens decreasesas you go down the group. For the metals, you will need to be given anactivity series. General equation:

A + BCAC + B

    where A is a metal.

    Here is an example of a displacement reaction in which a metal is involved:

Cu(s) + 2AgNO3(aq)2Ag(s) + Cu(NO3)2(aq)

    General equation:

A + BCBA + C

    where A is a nonmetal.

    Here is an example of a displacement reaction where a nonmetal is involved:

Cl2(g) + 2NaI(aq)2NaCl(aq) + I2(s)

    Double replacement or displacement reaction:In this type of reaction, two compounds react to form two newcompounds. The formation of a molecular compound such as water, theformation of a gas, or the formation of a precipitate usually drivesthese reactions. Here’s the general equation:

AB + CDAD + CB

    And here are a couple of examples:

Pb(NO3)2(aq) + 2KI(aq)2KNO3(aq) + PbI2(s)

HCl(aq) + NaOH(aq)H2O(l) + NaCl(aq)

    Combustion reaction: Inthis type of reaction, often a hydrocarbon is burned in the presence ofoxygen gas to form carbon dioxide (in a complete combustion) or carbonmonoxide (in an incomplete combustion, due to a limited amount ofoxygen). Here is the general equation in the presence of plenty ofoxygen:

CxHy + O2(g)CO2(g) + H2O(l) or (g)

    An example of this is seen when methane gas is burned in the presence of excess oxygen (Bunsen burner reaction):

CH4(g) + 2O2(g)CO2(g) + 2H2O(g)

    Here is the general equation for when a hydrocarbon is burned in an incomplete combustion (oxygen is in limited supply):

CxHy + O2(g)CO(g) + H2O(l)

    Hydrolysis reaction: A reaction that involves water. Here is the general equation for a hydrolysis reaction: