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: Combination (Synthesis) Decomposition Single Replacement Double Replacement Combustion

Synthesis Reactions Two or more substances combine to form a more complex substance. The general form is A + X AX Example: Magnesium + oxygen  magnesium oxide 2Mg + O2  2MgO

Magnesium + Oxygen

Synthesis Reactions Combination reactions may also be called composition or synthesis reactions.

Synthesis Reactions K + Cl2  Write the ions: K+ Cl- Balance the charges: KCl Balance the equation: 2K + Cl2  2KCl

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

Electrolysis of Water

Decomposition Reactions CaCO3  CaO + CO2 H2CO3  H2O + CO2 Ca(OH)2  CaO + H2O 2KClO3  2KCl + 3O2 Zn(ClO3)2  ZnCl2 + 3O2

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

Single Replacement 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 Replacement 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:

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

Double Replacement 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 SO42- 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 Replacement CuSO4 + Na2CO3  Cu2+ combines with CO32- to form CuCO3. Na+ combines with SO42- to form Na2SO4. CuSO4 + Na2CO3  CuCO3 + Na2SO4

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 Combination Ca + 2H2O  Ca(OH)2 + H2 Single replacement

Practice 2CO + O2  2CO2 2KClO3  2KCl + 3O2 Combination and combustion 2KClO3  2KCl + 3O2 Decomposition

Practice FeS + 2HCl  FeCl2 + H2S Zn + HCl  ? Double replacement Single replacement Zn + 2HCl  ZnCl2 + H2