Types of Chemical Reactions

Outline  Types of Reactions – the 5 types  Synthesis and Decomposition

Chemical Reactions  Chemical reactions can be grouped into five categories:  Synthesis/Combination  Decomposition  Single displacement  Double displacement  Combustion

Chemical Reactions  Today we will focus on synthesis and decomposition LEARNING GOAL: Be able to identify and predict the products for synthesis and decomposition reactions

Synthesis Reaction  Synthesis Reaction – Two or more substances (elements or compounds) react to form ONE product. Combination of smaller atoms/molecules into larger molecules.  Usually exothermic (energy is produced)  Can occur naturally or by an initial application of energy (heat, flame, UV light, use of catalyst)

Synthesis Reaction A + B  AB  eg. 2H 2 + O 2  2H 2 0 2Na (s) + Cl 2(g)  2NaCl (s) + energy

Synthesis Reaction

Predicting Products   Metal + oxygen → metal oxide (basic oxide) EX. 2Mg (s) + O 2(g) → 2MgO (s)   Nonmetal + oxygen → nonmetallic oxide (acidic oxide) EX. C (s) + O 2(g) → CO 2(g)   Metal oxide + water → metallic hydroxide (base) EX. MgO (s) + H 2 O (l) → Mg(OH) 2(s)   Nonmetallic oxide + water → acid EX. CO 2(g) + H 2 O (l) → ; H 2 CO 3(aq)   Metal + nonmetal → salt EX. 2 Na (s) + Cl 2(g) → 2NaCl (s)   A few nonmetals combine with each other. EX. 2P (s) + 3Cl 2(g) → 2PCl 3(g)   These two reactions must be remembered: N 2(g) + 3H 2(g) → 2NH 3(g) NH 3(g) + H 2 O (l) → NH 4 OH (aq)

Decomposition Reaction  Decomposition Reaction – ONE reactant produces two or more products. Splitting of large molecules into elements or smaller molecules.  Usually endothermic (requires energy)  Can require energy in the form of heat, electricity, catalyst, UV light  *some decomposition rxns occur at room temperature

Decomposition Reaction AB  A + B  Eg. 2H 2 0  2H 2 + O 2 2NaCl (s)  2Na (s) + Cl 2(g) (heat/electricity required) 2NaCl (s)  2Na (s) + Cl 2(g) (heat/electricity required)

Decomposition Reaction

Predicting Products   Metallic carbonates, when heated, form metallic oxides and CO 2(g). EX. CaCO 3(s) → CaO (s) + CO 2(g)   Most metallic hydroxides, when heated, decompose into metallic oxides and water. EX. Ca(OH) 2(s) → CaO (s) + H 2 O (g)   Metallic chlorates, when heated, decompose into metallic chlorides and oxygen. EX. 2KClO 3(s) → 2KCl (s) + 3O 2(g)   Some acids, when heated, decompose into nonmetallic oxides and water. EX. H 2 SO 4 → H 2 O (l) + SO 3(g)   Some oxides, when heated, decompose. EX. 2HgO (s) → 2Hg (l) + O 2(g)   Some decomposition reactions are produced by electricity. EX. 2H 2 O (l) → 2H 2(g) + O 2(g) EX. 2NaCl (l) → 2Na (s) + Cl 2(g)