Classification of Chemical Reactions Types of Chemical Reactions

Classification of Chemical Reactions

Types of Chemical Reactions • • • Synthesis Decomposition Single Replacement Double Replacement Combustion

Synthesis Reactions • A reaction in which two or more simple substances (elements or compounds) react to form one new substance. • A + B AB • Example: 2 H 2 + O 2 2 H 2 O Ca. O + CO 2 Ca. CO 3

Decomposition Reactions • A reaction in which one substance breaks down into two or more simple substances • AB A + B • Example: 2 H 2 O 2 2 H 2 O + O 2 2 KCl. O 3 2 KCl + 3 O 2

Single Replacement Reactions • A reaction in which an uncombined element replaces another element in a compound • A + BC AC + B • “Like replaces like” – metals replace metals and nonmetals replace nonmetals

Single Replacement Reactions (continued) • Examples: Mg + Cu. SO 4 Mg. SO 4 + Cu (Mg and Cu are both metals) Cl 2 + Na. Br Na. Cl + Br 2 (Cl and Br are both nonmetals) • In order for the reaction to take place, the uncombined element must be more reactive than the ion it is replacing.

Reactivity Table Most Active Metals Least Active Metals Li Rb K Ca Na Mg Al Mn Zn Fe Ni Sn Pb Cu Ag Pt Au Most Active Nonmetals F Cl Br I Least Active Nonmetals

Which of the following reactions can take place? I 2 + Na. F F 2 + Na. I Mg + HCl Mg. Cl 2 + H 2 Cu + Mg. SO 4 Cu. SO 4 + Mg K + Na. OH KOH + Na

Double Replacement Reactions • A reaction in which two positive ions replace each other in compounds • AB + CD AD + CB • In order for this type of reaction to occur, one of the following must happen: a precipitate is formed, a gas is formed, or one of the products must be covalent.

Double Replacement Reactions (continued) • Examples: Na 2 S + Cu(NO 3)2 Cu. S+ 2 Na. NO 3 (a precipitate is formed) 2 Na. CN + H 2 SO 4 2 HCN + Na 2 SO 4 (a gas is formed) Na. OH + HCl Na. Cl + H 2 O (a covalent compound is formed)

Combustion Reaction • A reaction in which a hydrocarbon reacts with oxygen to produce carbon dioxide and water • Cx. Hy + O 2 CO 2 + H 2 O • Example: CH 4+ 2 O 2 CO 2 + 2 H 2 O C 6 H 12 O 6 + 6 O 2 6 CO 2 + 6 H 2 O

Review Classify each of the following reactions by type and then balance the equation: Pb(NO 3)2 + K 2 Cr. O 4 Pb. Cr. O 4+ KNO 3 Cl 2 + KI KCl + I 2 C 3 H 6 + O 2 CO 2 + H 2 O Al(OH)3 Al 2 O 3 + H 2 O Li + O 2 Li 2 O HCl + Fe 2 O 3 Fe. Cl 3 + H 2 O Mg. CO 3 Mg. O + CO 2 Ba(CN)2 + H 2 SO 4 HCN + Ba. SO 4

Classifying Reactions Based on Energy Changes • Exothermic reactions are reactions in which heat/energy is released • Example: 2 C 4 H 10 + 13 O 2 8 CO 2 + 10 H 2 O • The container often feels warm during exothermic reactions • reactions involving explosions and burning are examples

Classifying Reactions Based on Energy Changes (continued) • Endothermic reactions are reactions in which heat/energy is absorbed • Example: 6 CO 2 + 6 H 2 O C 6 H 12 O 6 + 6 CO 2 (photosynthesis) Na. HCO 3 + HCl Na. Cl + H 2 O + CO 2 • The container often feels cold during endothermic reactions • Reactions involving cooking or heating are often examples

Review • Identify each of the following as either exothermic or endothermic: Baking a cake Exploding dynamite Burning a piece of paper A chemical ice pack Hand warmers