Chemical Equations

1. Chemical Equations

2. H2 + O2 H2O I. Writing Chemical Equations A. Reactants  Products B. Balancing chemical equations 1) Numbers are written in front of each molecule so that there are the same number of each atom on both sides… these numbers are called coefficients

3. 2 2 2 2 2) It doesn’t matter which atom you decide to balance first 3) DO NOT change ANY subscripts 4) Subscript x coefficient = # of that atom H2 + O2 H2 O 5) Recheck everything before you quit the problem

4. a) SO2 + O2 => SO3 2 2 Try balancing these: b) Fe2O3 + H2 => Fe + H2O 2 3 3 c) C2H6 + O2 => CO2 + H2O 2 3 7 2 C2H6 + O2 => CO2 + H2O 7 6 2 4 • Aluminum carbonate + hydrochloric acid => aluminum • chloride + carbonic acid

5. Aluminum carbonate + hydrochloric acid => aluminum • chloride + carbonic acid

6. II.Five basic Types of Chemical Reactions Synthesis (composition) Decomposition Single Replacement Double Replacement Combustion

7. Before we begin ……. There are 7 elements that MUST be written with a subscript of 2 whenever they are by themselves in an equation: I2 Br2 Cl2 F2 O2 I N2 H2 New House Bring Clay For Br I N Cl H O F Our

8. Synthesis (composition) * Template: A + X => AX Clue 1: Only ONE product is formed Clue 2 : Two elements as reactants Clue 3 : metal oxide + water => metal hydroxide Clue 4: non metal oxide + water => acid

9. Synthesis (composition) Template: A + X => AX Clue 1: Only ONE product is formed Clue 2: Two elements as reactants Examples: 2 Na + Cl2 => 2 NaCl 2 H2 + O2 => 2 H2O

10. Synthesis (composition) Template: A + X => AX Clue 3: metal oxide + water => metal hydroxide Examples: Na2O + H2O => 2 NaOH calcium oxide + water => ??? CaO + H2O => Ca(OH)2

11. Synthesis (composition) Template: A + X => AX Clue 4: non metal oxide + water => acid Examples: CO2 + H2O => H2CO3 sulfur trioxide + water => ????? SO3 + H2O => H2SO4

12. Synthesis (composition) Practice: a) K2O + H2O => b) N2O5 + H2O => c) Sodium is added to chlorine gas d) Lithium oxide is added to water

13. 2) Decomposition Reaction * Template: AX => A + X Clue 1: metal chlorates => metal chloride + oxygen Examples: KClO3 => KCl + O2 barium chlorate => ??? + ??? Ba(ClO3)2 => BaCl2 + O2 (oxygen is proven by the glowing splint test) 2 2 3 3

14. 2) Decomposition Reaction Template: AX => A + X Clue 2: metal carbonates => metal oxide + carbon dioxide CaCO3=> ??? + ??? CaCO3=> CaO+ CO2 (CO2 is proven by the flaming splint test)

15. 2) Decomposition Reaction Template: AX => A + X Clue 3: metal hydroxides=> metal oxide + water Example: Ca(OH)2 => CaO + H2O

16. 2) Decomposition Reaction Template: AX => A + X Clue 4: Two elements => separate elements 2 H2O => 2 H2 + O2 2 HgO => 2 Hg + O2

17. 3) Single Replacement Template: A + BX => AX + B AX + Y => AY + X Clue 1: free metal replaces the “front” element in a compound Fe + CuSO4 => FeSO4 + Cu Na + HOH => NaOH + H2 (metals replace the “front” element) 2 2 2

18. ALERT!!!!!! 2 Na + 2HOH => 2NaOH + H2 (note how water is written) NOT…. 2 Na + H2O => Na2O + H2

19. 3) Single Replacement Template: A + BX => AX + B AX + Y => AY + X Clue 2: free non metal replaces the non metal in a compound Example: Cl2 + NaBr => NaCl + Br2 2 2

20. 4) Double Replacement Template: AX + BY => AY + BX Clue 1: two compounds are reacting Examples: AgNO3 + NaCl => AgCl + NaNO3 (switch the “front” elements) lead (II) acetate is added to sodium iodide Pb(C2H3O2)2 + 2NaI => PbI2 + 2NaC2H3O2

21. 4) Double Replacement Template: AX + BY => AY + BX Clue 2: Double replacement reactions always form one of these: - a gas - water - a precipitate (something not soluble)

22. 4) Double Replacement Predicting what precipitate forms: Are these soluble? yes yes LiCl (NH4)2SO4 no CuOH yes Na2CO3 no AgCl

23. 5) Combustion Reactions Template: AX + O2 => AO + BO Clue 1: Statement includes “burning” which means to add oxygen gas Example: CH4 + 2 O2 => CO2 + 2 H2O