Types of Chemical Reactions

Synthesis Reactions Smaller atoms/compounds combine to form larger molecules Also known as combination or addition reactions A + B  AB 2H 2 + O 2  2H 2 O

Synthesis Reaction

Synthesis Reactions -Examples i) A metal reacts with oxygen to produce an oxide Na (s) + O 2(g)  Na 2 O (s) Is this equation balanced? ii) A metal reacts with a non-metal to form a binary compound K (s) + Cl 2(g)  KCl (s) Is this equation balanced? iii) A compound reacts with an element to form a new compound PCl 3 (l) + Cl 2(g)  PCl 5(s) Is this equation balanced?

Examples of synthesis Metal + oxygen → metal oxide 2Mg(s) + O 2 (g) → 2MgO(s)‏ Nonmetal + oxygen → nonmetallic oxide C(s) + O 2 (g) → CO 2 (g) Metal oxide + water → metallic hydroxide MgO(s) + H 2 O(l) → Mg(OH) 2 (aq) Nonmetallic oxide + water → acid CO 2 (g) + H 2 O(l) → H 2 CO 3 (aq) (one more oxygen) Metal + nonmetal → ionic compound (salt ) Mg(s) + Cl 2 (g) → MgCl 2 (s) A few nonmetals combine with each other. 2P(s) + 3Cl 2 (g) → 2PCl 3 (g) ff

Oxides When an element combines with oxygen an oxide is formed Metals react with oxygen to form metal oxides Metal oxides are always solids react in water to form basic solutions are also called basic oxides Recall: Properties of basic solutions Turn red litmus blue and colourless phenolphthalein indicator pink

Metal Oxides - Example Ca (s) + O 2(g)  CaO (s) CaO (s) + H 2 O (l)  Ca(OH) 2(aq) 22 metal oxide basic solution metal hydroxide

Oxides Non-metals react with oxygen to form non-metal oxides Non-metal oxides are often gases or liquids react in water to form acidic solutions are also called acidic oxides Recall: Properties of acidic solutions Turn blue litmus red and blue coloured bromothymol blue (BTB) indicator yellow

Non-metal Oxides - Example N 2 (g) + O 2(g)  NO 2 (g) NO 2 (g) + H 2 O (l)  HNO 3(aq) + NO (g) 2 non-metal oxide acidic solution 2 23

Decomposition Reaction The splitting of a large molecule into elements or smaller compounds AB  A + B 2H 2 O  2H 2 + O 2 Complimentary to synthesis reaction

Decomposition Reaction

Decomposition Reactions-Examples i)Water decomposes into its elements H 2 O (l)  H 2(g) + O 2(g) ii)Hydrazine (a rocket fuel) decomposes N 2 H 4 (l)  NH 3(g) + N 2(g) 22 34

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

Homework Worksheet Oxides Investigation 1– Read and make your prediction (on a separate sheet) Journal (for portfolio) Is waste gasification a viable solution to landfill problems? Provide the pros and cons of introducing this form of waste management in Ontario.