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

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

Some types of synthesis reactions: Some types of synthesis reactions: Combination of elements Combination of elements K + Cl 2  K + Cl 2  One product will be formed One product will be formed

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

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

Decomposition Reactions One substance reacts to form two or more substances. One substance reacts to form two or more substances. The general form is AX  A + X The general form is AX  A + X Example: Example: Water can be decomposed by electrolysis. Water can be decomposed by electrolysis. 2H 2 O  2H 2 + O 2 2H 2 O  2H 2 + O 2

Single Displacement Reactions A metal will replace a metal ion in a compound. A metal will replace a metal ion in a compound. The general form is A + BX  AX + B The general form is A + BX  AX + B A nonmetal will replace a nonmetal ion in a compound. A nonmetal will replace a nonmetal ion in a compound. The general form is The general form is Y + BX  BY + X Y + BX  BY + X

Single Displacement Reactions Examples: Examples: Ni + AgNO 3  Ni + AgNO 3  Nickel replaces the metallic ion Ag +. Nickel replaces the metallic ion Ag +.

Single Displacement Reactions Not all single displacement reactions that can be written actually happen. Not all single displacement reactions that can be written actually happen. The metal must be more active than the metal ion. The metal must be more active than the metal ion. Aluminum is more active than iron in Al + Fe 2 O 3 Aluminum is more active than iron in Al + Fe 2 O 3

Al + Fe 2 O 3  Al + Fe 2 O 3  2Al + Fe 2 O 3  2Fe + Al 2 O 3 2Al + Fe 2 O 3  2Fe + Al 2 O 3

Single Displacement Reactions An active nonmetal can replace a less active nonmetal. An active nonmetal can replace a less active nonmetal. Ex- halogens (F 2, Cl 2, Br 2, I 2 ) Ex- halogens (F 2, Cl 2, Br 2, I 2 ) F 2 is the most active and I 2 is the least. F 2 is the most active and I 2 is the least. Cl 2 +2 NaI  2 NaCl + I 2 Cl 2 +2 NaI  2 NaCl + I 2

Double Displacement Reactions Ions of 2 compounds exchange places with each other. Ions of 2 compounds exchange places with each other. The general form is The general form is AX + BY  AY + BX AX + BY  AY + BX

Combustion Reaction When a substance combines with oxygen, a combustion reaction results. 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 + O 2  2MgO. The combustion reaction may also be an example of an earlier type such as 2Mg + O 2  2MgO. The combustion reaction may be burning of a fuel. The combustion reaction may be burning of a fuel.

Combustion Reaction Methane, CH 4, is natural gas. Methane, CH 4, is natural gas. When hydrocarbon compounds are burned in oxygen, the products are water and carbon dioxide. When hydrocarbon compounds are burned in oxygen, the products are water and carbon dioxide. CH 4 + O 2  CO 2 + H 2 O CH 4 + O 2  CO 2 + H 2 O

Oxidation-Reduction Reaction where electrons are exchanged Reaction where electrons are exchanged Oxidation-lose electrons Oxidation-lose electrons Reduction-gain electrons Reduction-gain electrons