Day 007­ Synthesis, Decomposition and Combustion
Synthesis Reactions
Definition of synthesis reactions: Two or more elements or compounds combine to form a new substance ie. A + B à C
A. Simple synthesis reactions
Definition of simple synthesis reactions:
One element reacts with one or more other elements to form a compound
Describe the two types of simple synthesis reactions and give two balanced examples of each.
Type 1: metal element or nonmetal element + oxygen à oxide
Eg. 1: 3 Fe (s) + O2 (g) à Fe3O2 (s)
Eg. 2: 2 H2 (g) + O2 (g) à 2H2O (g)
Type 2: metal + non‐metal à binary compound
Eg. 1:
2 K (s) + Cl2 (g) à 2KCl (s)
Eg. 2 (think of one):
B. Synthesis reactions involving compounds as reactants
Type 1: non­metallic oxide reacting with water.
non­metallic oxide + H2O à acid
What type of product is formed in these type of reactions. acid Look for the hydrogen cations with an oxyanion Give two examples (balanced!): Eg 1: SO3 (g) + H2O (l) à H2 SO4 (aq)
Eg 2: CO2 + H2O à H2 CO3 (aq)
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Day 007­ Synthesis, Decomposition and Combustion
Type 2: metallic oxide reacting with water.
What type of product is formed in these type of reactions. metal hydroxide = base
Give two examples (balanced!): Eg 1: CaO (s) + H2O (l) à Ca(OH)2 (aq)
Eg 2: Na2O + H2O à 2 NaOH
Do synthesis reactions always produce only one type of product? No (you can only guess at what will happen)
Give two examples: Eg 1: C (s) + O2 (g) à CO2 (g)
Eg 2: 2 C (s) + O2 (g) à 2 CO (g)
Decomposition Reactions
Define a decomposition reaction: a compound breaks down into elements or other compounds
What are two types of decomposition reactions and give an example of each.
Type 1: compound à component elements
Eg 2H2O (l) à 2H2 (g) + O2 (g)
( electricity passed through water)
Type 2: compound à other compounds
Eg. NH4NO3(s) à N2O (g) + 2H2O (g)
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Day 007­ Synthesis, Decomposition and Combustion
Combustion Reactions
Define a complete combustion reaction: reaction of a compound or element with oxygen to form the most common oxide of that element or compound. Ex. A carbon­containing compound undergoes combustion to form: CO2 (g)
A sulfur containing compound undergoes combustion to form: SO2 (g)
Combustion reactions are usually also accompanied by the production of: heat and light What are the main products for a compound containing carbon, hydrogen, and oxygen: CO2 and H2O
Eg. C2H5OH(l) + 3O2 (g)à 2 CO2 (g) + 3H2O (g)
Complete combustion reactions are often also synthesis reactions. Metals undergo combustion to form their stable oxide.
Eg. 2 Mg(s) + O2 (g) à 2MgO (s)
Define an incomplete combustion reaction: occurs in the absence of sufficient oxygen leading to CO and H2O
Why is it an important reaction to be aware of? CO is deadly, you should always make sure there is enough oxygen in your indoor environment for gas furnaces, stoves and/or fireplaces
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