Chemical Reactions Part 1: Decomposition and Synthesis Reactions

Objectives -To identify decomposition and synthesis chemical reactions -To predict the products of these two types of reactions 2

Symbols in Equations The arrow ( → ) separates the reactants from the products (s) = solid: Fe (s) (g) = gas: CO 2(g) (l) = liquid: H 2 O (l)

Symbols in Equations double arrow indicates a reversible reaction (more later) heat is supplied to the reaction a catalyst is supplied (i.e. platinum)

Classifying and Predicting Chemical Reactions Oxidation-Reduction reactions - electrons are transferred from one atom to another There are 5 classifications: –Decomposition –Synthesis –Combustion –Single displacement –Double displacement (ionic) 5

Decomposition Reactions Decompose = fall apart Decomposition reactions- one compound decomposes into two or more elements or compounds Key: only 1 reactant Usually involves energy or heat 6

Decomposition Binary compounds (two elements) will split into those two elements: AB  A + B Tertiary compounds (three elements) will have one element in BOTH products ABC  AB + BC 7

Decomposition Reactions A. Electrolysis (adding electricity) of compounds produces the elements 2 H 2 O  2 H 2 + O 2 2 NaCl  2 Na + Cl 2 8

Decomposition Reactions B. Metallic (any positive ion) chlorates decompose into metallic chlorides and oxygen when heated 2 KClO 3  2 KCl + 3 O 2 C. Metallic carbonates decompose into metallic oxides and carbon dioxide when heated CaCO 3  CaO + CO 2 9

Decomposition Reactions D. Hydrated compounds yield the anhydrous compound and water when heated CuSO 4  5 H 2 O  CuSO H 2 O E. Oxides of the less active metals (see activity series) form the metal and oxygen when heated 2 HgO  2 Hg + O 2 10

Decomposition Reactions F. Acids (hydrogen with negative ion) decompose into water and nonmetallic oxides H 2 CO 3  H 2 O + CO 2 2 H 3 PO 4  P 2 O H 2 O G. Bases (metallic hydroxides) decompose into water and metallic oxides Ca(OH) 2  CaO + H 2 O 11

Decomposition Reactions H. Peroxides decompose into oxides and oxygen. 2 K 2 O 2  2 K 2 O + O 2 2 H 2 O 2  2 H 2 O + O 2 water is the oxide of hydrogen 12

Synthesis Reactions Synthesize = to make or put together Synthesis reactions-two or more elements or compounds unite to form one product Key: 2 elements OR two compounds when both are oxides with only one product 13

Synthesis Reactions A.Oxygen combines with most elements to form oxides 2 Mg + O 2  2 MgO C + O 2  CO 2 B. Metallic elements + nonmetallic elements yield ionic compounds (ionic compounds called salts) 2 Al + 3 Cl 2  2 AlCl 3 2 K + I 2  2 KI 14

Synthesis Reactions C. Nonmetallic elements tend to combine with each other to form covalent (molecular) compounds S F 2  8 SF 2 P Cl 2  4 PCl 3 15

Synthesis Reactions D. Oxides of metals + water form bases (metallic hydroxides) Water is an oxide! CaO + H 2 O  Ca(OH) 2 Na 2 O + H 2 O  2 NaOH 16

Synthesis Reactions E. Oxides of nonmetals + water form acids- acids usually made from an “ate” ion P 2 O H 2 O  2 H 3 PO 4 SO 3 + H 2 O  H 2 SO 4 F. Oxides of metals + oxides of nonmetals yield ionic compounds- usually contain an “ate” ion Na 2 O + SO 3  Na 2 SO 4 17

Objectives -To identify decomposition and synthesis chemical reactions -To predict the products of these two types of reactions 18