Chemical Reactions Types of Chemical Reactions

Chemical Reactions 5 Types of Chemical Reactions » synthesis » decomposition » single-displacement » double-displacement » combustion reactions

1. Synthesis Reactions  In a synthesis reaction, aka composition reaction  two or more substances combine to form a new compound  A and X can be elements or compounds  AX is a compound A + X AX

Synthesis Reactions with Oxygen  combination of an element with oxygen to produce an oxide of the element  Almost all metals react with oxygen to form oxides  Group 2 elements form oxides with the formula MO, where M represents the metal  The Group 1 metals form oxides with the formula M 2 O 2Mg(s) + O 2 (g) 2MgO(s)

Synthesis Reactions with Sulfur  The Group 1 and Group 2 elements react similarly with sulfur, forming sulfides with the formulas M 2 S and MS  (M = metal) 16Rb(s) + S 8 (s) 8Rb 2 S(s) 8Ba(s) + S 8 (s) 8BaS(s)

Synthesis Reactions with Halogens Most metals react with the Group 17 elements, the halogens, to form either ionic or covalent compounds » Group 1 metals react with halogens to form ionic compounds with the formula MX, where M is the metal and X is the halogen » Group 2 metals react with the halogens to form ionic compounds with the formula MX 2 » Fluorine is so reactive that it combines with almost all metals 2Na(s) + Cl 2 (g) 2NaCl(s) Mg(s) + F 2 (g) MgF 2 (s)

Mg(s) + O2(g) → MgO

2. Decomposition Reactions  In a decomposition reaction, a single compound undergoes a reaction that produces two or more simpler substances.  opposite of synthesis reactions  AX is a compound  A and X can be elements or compounds AX A + X

Decomposition Reactions of Binary Compounds  The decomposition of a substance by an electric current is called electrolysis  Oxides of the less-active metals, which are located in the lower center of the periodic table, decompose into their elements when heated

Decomposition of Acids Certain acids decompose into nonmetal oxides and water (carbonic acid)

2KClO 3 (s)  2KCl(s) + 3O 2 (g) C 6 H 12 O 6 (s) + 6O 2 (g)  6CO 2 (g) + 6H 2 O(g)

3. Single-Displacement Reactions  In a single-displacement reaction, aka replacement reaction  one element replaces a similar element in a compound  Many take place in aqueous solution  A, B, X, and Y are elements. AX, BX, and BY are compounds A + BX AX + B or Y + BX BY + X

Displacement of a Metal in a Compound by Another Metal  Aluminum is more active than lead 2Al(s) + 3Pb(NO 3 ) 2 (aq) 3Pb(s) + 2Al(NO 3 ) 3 (aq)

Displacement of Hydrogen in Water by a Metal  The most-active metals, such as those in Group 1, react vigorously with water to produce metal hydroxides and hydrogen  Less-active metals, such as iron, react with steam to form a metal oxide and hydrogen gas 2Na(s) + 2H 2 O(l) 2NaOH(aq) + H 2 (g) 3Fe(s) + 4H 2 O(g) Fe 3 O 4 (s) + 4H 2 (g)

Single Displacement of Hydrogen in an Acid by a Metal  The more-active metals react with certain acidic solutions, such as hydrochloric acid and dilute sulfuric acid, replacing the hydrogen in the acid  The reaction products are a metal compound (a salt) and hydrogen gas Mg(s) + 2HCl(aq) H 2 (g) + MgCl 2 (aq)

Single Displacement of Halogens  In Group 17 each element can replace any element below it, but not any element above it  Fluorine is the most-active halogen so it can replace any of the other halogens in their compounds Cl 2 (g) + 2KBr(aq) 2KCl(aq) + Br 2 (l) F 2 (g) + 2NaCl(aq) 2NaF(aq) + Cl 2 (g) Br 2 (l) + KCl(aq) no reaction

4. Double-Replacement Reactions  In double-displacement reactions, the ions of two compounds exchange places in an aqueous solution to form two new compounds

Double-Replacement Reactions A double-displacement reaction is represented by the following general equation » A, X, B, and Y in the reactants represent ions » AY and BX represent ionic or molecular compounds AX + BY AY + BX

Double-Replacement Reactions  Formation of a Precipitate  The formation of a precipitate occurs when the cations of one reactant combine with the anions of another reactant  The precipitate forms as a result of the very strong attractive forces between the Pb 2+ cations and the I − anions 2KI(aq) + Pb(NO 3 ) 2 (aq) PbI 2 (s) + 2KNO 3 (aq)

Double-Replacement Reactions  Formation of a Gas  Formation of Water FeS(s) + 2HCl(aq) H 2 S(g) + FeCl 2 (aq) HCl(aq) + NaOH(aq) NaCl(aq) + H 2 O(l)

5. Combustions Reactions  In a combustion reaction, a substance combines with oxygen, releasing a large amount of energy in the form of light and heat  Combustion of hydrogen  Combustion of propane 2H 2 (g) + O 2 (g) 2H 2 O(g) C 3 H 8 (g) + 5O 2 (g) 3CO 2 (g) + 4H 2 O(g)