Types of chemical reactions – Part A Dr. Chin Chu River Dell Regional High School

Chemical changes (reactions) 2H2 + O2 2H2O 2NaOH(aq) + CuCl2(aq)  2NaCl(aq) + Cu(OH)2(s) Cu + 2AgNO3  2Ag + Cu(NO3)2 NH3 + H2O  NH4OH NH4NO3(s)  N2O(g) + 2H2O(g) How could we get a handle on those changes?

Organization of chemical reactions ® O C O C + C + O2  CO2 Chemical reactions are merely rearrangements of atoms into different combinations called compounds. There got to be some patterns that can be categorized into different types.

Unit objectives There are millions of reactions. Can’t remember them all. Fall into several categories. Will learn 5 types. Will be able to predict the products. For some we will be able to predict whether they will happen at all. Will recognize them by the reactants

Do you see the patterns? exercise Balancing the following chemical equations: aluminum(s) + iodine(s)  aluminum iodide(s) sulfur trioxide + water  sulfuric acid (H2SO4) lithium oxide + water  lithium hydroxide Do you see the patterns?

Synthesis reactions Called also combination reactions General Equation: A + B ® AB Animation: 2 elements, or compounds combine to make one compound. Mg +O2 ® MgO SO2 + H2O ® H2SO3

Types of Synthesis Reactions Combination of elements Element + element ® compound 2Hg + O2 ® 2HgO 9Mg + 3N2 ® 3Mg3N2 Nonmetalic Oxides + water ® acid SO2 + H2O ® H2SO3 P4O10 + 6H2O ® 4H3PO4

Types of Synthesis reactions Metalic oxides + water ® base MgO + H2O ® Mg(OH)2 Na2O + H2O ® 2NaOH Metallic oxides + nonmetallic oxide ® salt MgO + CO2 ® MgCO3 CaO + SiO2 ® CaSiO3

Do you see the patterns? exercise Watch the following video clips and write balanced equations: 1. Thermal decomposition of copper(II) nitrate When heated, solid copper(II) nitrate decomposes into copper(II) oxide, nitrogen dioxide and water vapor. 2. Thermal decomposition of zinc carbonate When heated, solid zinc carbonate decomposes into solid zinc oxide and carbon dioxide gas. Do you see the patterns?

Decomposition reactions Substances break apart. General Form: AB ® A + B Animation: Decomposition reactions are reverse of synthesis, with exceptions.

Decomposition reactions Special Cases Metal Chlorate ® metal chloride + oxygen 2KClO3 ®2KCl + 3O2 Metal bicarbonate ® metal oxide + carbon dioxide + water 2NaHCO3 ® Na2O + 2CO2 + H2O

Decomposition reactions Special Cases Most oxides are stable, only few decompose: 2HgO ® Hg + O2 Electrolysis of molten salt (decomposition by electricity) is the only means for decomposition for some substances: 2H2O ® 2H2 + O2 2NaCl ® 2Na + Cl2

Do you see the patterns? demos The methane bubble The perfect combution (ethanol) http://www.youtube.com/watch?v=Lb-KB_BshUc&NR=1 Burning of methanol Do you see the patterns?

Combustion reactions A compound composed of only C, H and maybe O is reacted with oxygen If the combustion is complete, the products will be CO2 and H2O. If the combustion is incomplete, the products will be CO and H2O.

exercises C4H10 + O2 ® (complete combustion) C4H10 + O2 ® (incomplete combustion) C6H12O6 + O2 ® (complete combustion) C8H8 +O2 ® (incomplete combustion)

More exercises Write a balanced equation for the complete combustion of each of these compounds. a) acetic acid, HC2H3O2 c) glycerol, C3H8O3 b) decane, C10H22 d) sucrose, C12H22O11 Write a balanced equation for the incomplete combustion of each of these compounds. a) glycerol, C3H8O3 c) acetic acid, HC2H3O2 b) glucose, C6H12O6 d) acetylene, C2H2