Types of Chemical Reactions

Writing Chemical Reactions

Types of Reactions

Many chemical reactions have defining characteristics which allow them to be classified as to type.

Types of Chemical Reactions

The five types of chemical reactions in this unit are: Synthesis Decomposition Single Displacement Double Displacement Combustion

Synthesis Reactions Two or more substances combine to form

one substance. The general form is A + X AX

Example:Magnesium + oxygen magnesium

oxide 2Mg + O2 2MgO

Synthesis Reactions

Synthesis reactions may also be called composition or combination reactions.

Some types of combination reactions: Combination of elements

K + Cl2 One product will be formed

Synthesis Reactions K + Cl2

Write the ions: K+ Cl-

Balance the charges: KCl

Balance the equation: 2K + Cl2 2KCl

Synthesis Reactions Some types of synthesis reactions:Oxide + water Nonmetal oxide + water acidSO2 + H2O H2SO3

Metal oxide + water baseBaO + H2O Ba(OH)2

Synthesis Reactions Some types of synthesis reactions:Metal oxides + nonmetal oxidesNa2O + CO2 Na2CO3CaO + SO2 CaSO3

Decomposition Reactions One substance reacts to form two or more

substances. The general form is AX A + X

Example:Water can be decomposed by

electrolysis. 2H2O 2H2 + O2

Decomposition Reactions Types of Decomposition Reactions: Decomposition of carbonatesWhen heated, some carbonatesbreak down to form an ox ide and carbon diox ide.CaCO3 CaO + CO2H2CO3 H2O + CO2

Decomposition Reactions Types of decomposition reactions:

Some metal hydrox ides decompose into ox ides and water when heated.Ca(OH)2 CaO + H2O

Note that this is the reverse of a similar synthesis reaction.

Decomposition Reactions Types of decomposition reactions:Metal chlorates decompose into

chlorides and oxygen when heated.2KClO3 2KCl + 3O2Zn(ClO3)2 ZnCl2 + 3O2

Some of these reactions are used in explosives.

Decomposition Reactions Some substances can easily

decompose: Ammonium hydroxide is actually

ammonia gas dissolved in water.NH4OH NH3 + H2O

Some acids decompose into water and an oxide.H2SO3 H2O + SO2

Single Displacement Reactions

A metal will replace a metal ion in a compound. The general form is A + BX AX + B

A nonmetal will replace a nonmetal ion in a compound. The general form is Y + BX BY + X

Single Displacement Reactions

Examples: Ni + AgNO3

Nickel replaces the metallic ion Ag+.The silver becomes free silver and the

nickel becomes the nickel(II) ion.Ni + AgNO3 Ag + Ni(NO3)2

Balance the equation:Ni + 2AgNO3 2Ag + Ni(NO3)

Single Displacement Reactions

Not all single replacement reactions that can be written actually happen.

The metal must be more active than the metal ion.

Aluminum is more active than iron in Al + Fe2O3 in the following reaction:

Thermite Reaction

Al + Fe2O3

Aluminum will replace iron(III) as was seen in the video.

Iron(III) becomes Fe and aluminum metal becomes Al3+.

2Al + Fe2O3 2Fe + Al2O3

Single Displacement Reactions

An active nonmetal can replace a less active nonmetal.The halogen (F2, Cl2, Br2, I2)

reactions are good examples.F2 is the most active and I2 is the

least.Cl2 +2 NaI 2 NaCl + I2

Double Displacement Reactions

Ions of two compounds exchange places with each other.The general form is AX + BY AY

+ BX

Metathesis is an alternate name for double replacement reactions.

Double Replacement NaOH + CuSO4

The Na+ and Cu2+ switch places. Na+ combines with SO4

2- to form Na2SO4. Cu2+ combines with OH- to form Cu(OH)2 NaOH + CuSO4 Na2SO4 + Cu(OH)2 2NaOH + CuSO4 Na2SO4 + Cu(OH)2

Double Displacement

CuSO4 + Na2CO3 Cu2+ combines with CO3

2- to form CuCO3.

Na+ combines with SO42- to form

Na2SO4. CuSO4 + Na2CO3 CuCO3 +

Na2SO4Na2CO3 + HCl

Double Displacement Na2CO3 + HCl Na+ combines with Cl- to form NaCl. H+ combines with CO3

2- to form H2CO3.

Na2CO3 + 2HCl 2NaCl + H2CO3 H2CO3 breaks up into H2O and CO2.

Double Displacement

The gas formed was carbon dioxide. The final balanced reaction is:

Na2CO3 + HCl NaCl + H2O + CO2. Balance the equation. Na2CO3 + 2HCl 2NaCl + H2O +

CO2

Combustion Reaction When a substance combines with

oxygen, a combustion reaction results.

The combustion reaction may also be an example of an earlier type such as 2Mg + O2 2MgO.

The combustion reaction may be burning of a fuel.

Combustion Reaction Methane, CH4, is natural gas. When hydrocarbon compounds are

burned in oxygen, the products are water and carbon dioxide.

CH4 + O2 CO2 + H2O CH4 + 2O2 CO2 + 2H2O

Combustion Reactions Combustion reactions involve light

and heat energy released. Natural gas, propane, gasoline, etc.

are burned to produce heat energy. Most of these organic reactions

produce water and carbon dioxide.

Practice Classify each of the following as to

type:

H2 + Cl2 2HCl Synthesis

Ca + 2H2O Ca(OH)2 + H2 Single displacement

Practice 2CO + O2 2CO2 Synthesis and combustion

2KClO3 2KCl + 3O2 Decomposition

Practice FeS + 2HCl FeCl2 + H2S Double displacement

Zn + HCl ? Single displacement Zn + 2HCl ZnCl2 + H2

Types of Chemical Reactions

Read Chapter 8-2

Review nomenclature

Do all of the practice exercises given in class.