3.2 Synthesis, Decomposition and Combustion Reactions

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

Synthesis and Decomposition Reactions Chemistry Prom 2014! Synthesis and Decomposition Reactions

Let’s come together…. Synthesis reaction – two more substances combine to form one new substance Two substances dancing alone decide to hook up… become a happy couple A + B  AB Geez I could use a mate. Man I’m lonely Satisfaction 

Synthesis Reaction Let’s come together…. Usually exothermic (energy is produced) Can occur naturally or by an initial application of energy (heat, flame, UV light, use of catalyst) Let’s come together….

Synthesis Reaction Let’s come together…. Geez I could use a mate. Man I’m lonely Satisfaction  Let’s come together….

Practice DIATOMIC ALERT! Al (s) + O2 (g)  Al3+O2- Al2O3 AlO Show the synthesis of solid aluminum and oxygen gas. What are the reactants? Al + O2 What are the products? It’s a synthesis reaction, so we know Al and O are going to make a compound…. If the products aren’t in the question you need to KRISS KROSS to figure it out! DIATOMIC ALERT! Al (s) + O2 (g)  Al3+O2- Al2O3 AlO

Practice A, B, and D C + O2  CO2 CaO + H2O  Ca(OH)2 H2O  H2 + O2 Which reactions are SYNTHESIS reactions? C + O2  CO2 CaO + H2O  Ca(OH)2 H2O  H2 + O2 2Na + Cl2  2NaCl Fe + CuSO4  FeSO4 + Cu 2K3PO4 + 3H2SO4  3K2SO4 + 2H3PO4 A, B, and D

Predicting Products Metal + oxygen → metal oxide (basic oxide) EX. 2Mg(s) + O2(g) → 2MgO(s) Nonmetal + oxygen → nonmetallic oxide (acidic oxide) EX. C(s) + O2(g) → CO2(g) Metal oxide + water → metallic hydroxide (base) EX. MgO(s) + H2O(l) → Mg(OH)2(s) Nonmetallic oxide + water → acid EX. CO2(g) + H2O(l) → ; H2CO3(aq) Metal + nonmetal → salt EX. 2 Na(s) + Cl2(g) → 2NaCl(s) A few nonmetals combine with each other. EX. 2P(s) + 3Cl2(g) → 2PCl3(g) These two reactions must be remembered: N2(g) + 3H2(g) → 2NH3(g) NH3(g) + H2O(l) → NH4OH(aq)

I don’t think this is working out… Decomposition reaction – one substance breaks into multiple substances A couple decides…well it is time to break up AB  A + B Satisfaction! I want to see other people I don’t think this is right for us… Satisfaction!

Decomposition Reaction 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. 2H20  2H2 + O2 2NaCl (s)  2Na (s) + Cl2(g) (heat/electricity required)

Decomposition Reaction I don’t think this is right for us… Satisfaction! I want to see other people Satisfaction!

Don’t forget to balance! Practice Show the decomposition water after electricity has passed through it. What are the reactants? Water! H2O What are the products? It’s a decomposition reaction, so we know the elements in water are going to break apart The question will specify if any compounds are formed DIATOMIC ALERT! H2O  H2 + O2 H + O Don’t forget to balance!

More Practice! C, D and F C + O2  CO2 CaO + H2O  Ca(OH)2 Which reactions are DECOMPOSITION reactions? C + O2  CO2 CaO + H2O  Ca(OH)2 H2O  H2 + O2 H2SO4 H2 + S + 2O2 Fe + CuSO4  FeSO4 + Cu K3PO4  K3P + 2O2 C, D and F

Predicting Products Metallic carbonates, when heated, form metallic oxides and CO2(g). EX. CaCO3(s) → CaO(s) + CO2(g) Most metallic hydroxides, when heated, decompose into metallic oxides and water. EX. Ca(OH)2(s) → CaO(s) + H2O(g) Metallic chlorates, when heated, decompose into metallic chlorides and oxygen. EX. 2KClO3(s) → 2KCl(s) + 3O2(g) Some acids, when heated, decompose into nonmetallic oxides and water. EX. H2SO4 → H2O(l) + SO3(g) Some oxides, when heated, decompose. EX. 2HgO(s) → 2Hg(l) + O2(g) Some decomposition reactions are produced by electricity. EX. 2H2O(l) → 2H2(g) + O2(g) EX. 2NaCl(l) → 2Na(s) + Cl2(g)

Combustion Reactions When a compound or element is reacted with O2 (g) to form the most common oxides that make up that compound. -These reactions usually accompany heat and light. Complete combustion – products H2O and CO2 Incomplete Combustion - products H2O and CO

Combustion Reactions Combustion reactions occur when a hydrocarbon reacts with oxygen gas. This is also called burning!!! In order to burn something you need the 3 things in the “fire triangle”: 1) A Fuel (hydrocarbon) 2) Oxygen to burn it with 3) Something to ignite the reaction (spark)

Combustion Reactions In general: CxHy + O2  CO2 + H2O Products in combustion are ALWAYS carbon dioxide and water. (although incomplete burning does cause some by-products like carbon monoxide) Combustion is used to heat homes and run automobiles (octane, as in gasoline, is C8H18)

Combustion Reactions Edgar Allen Poe’s drooping eyes and mouth are potential signs of CO poisoning.