1. Balancing chemical equations

2. WRITING CHEMICAL EQUATIONS Chemical equations should show : (a) formulas of the reactants & products (b) their states of matter (ie s, l, g, aq) (c) the numbers of reacting particles. An equation must balance. i.e. the type and number of atoms in the reactants and products must match. It must balance for CHARGES too!

3. then (c) either O or H atoms balance TO BALANCE AN EQUATION: 1.Write accurate formulas for each reactant and product 2.Show states of matter 3.Balance the equation by adding numbers IN FRONT OF the formulas (DO NOT CHANGE FORMULAS!) to make the numbers of: first (a) metal atoms balance then (b) any other atoms EXCEPT O and H balance

4. e.g.1Potassium hydroxide solution + sulphuric acid solution  potassium sulphate solution + water Formulas? States? Metal? Not O or H? O or H? KOH + H 2 SO 4  K 2 SO 4 + H 2 O (aq) (aq) (aq) (l) i.e. S 2 2

5. e.g.2Solid calcium nitrate  calcium oxide solid + nitrogen dioxide gas + oxygen gas Formulas? Ca(NO 3 ) 2 NO 2 CaO O2O2  ++ States? (s) (g) Metal? 1 1 Not O or H? 2 O or H? ½ x 2 to remove fractions Ca(NO 3 ) 2 NO 2 CaOO2O2  +(s) (g) 2 24 + i.e. N

6. e.g.3Sodium metal + liquid water  Aqueous sodium hydroxide + hydrogen gas Formulas? States? Metal? Not O or H? O or H? x 2 to remove fractions Na + H 2 O  NaOH + H 2 (s) (l) (aq) (g) Not applicable ½ 2 Na + 2H 2 O  NaOH + H 2 (s) (l) (aq) (g) 1

7. Write the balanced full equations for the reactions of : (1) Solid sulphur + oxygen gas  sulphur dioxide gas. (2) Sulphur trioxide solid + water  sulphuric acid solution. (3) Barium metal + water  hydrogen gas + barium hydroxide solution (4) Methane (CH 4 ) gas + oxygen  carbon dioxide gas + steam (5) Solid copper(II) nitrate  Solid copper(II) oxide + nitrogen dioxide gas + oxygen gas (6) sodium oxide solid + dilute hydrochloric acid  sodium chloride solution + water (7) copper (II) oxide solid + dilute nitric acid  copper(II) nitrate solution + water (8) potassium hydroxide solution + dilute sulphuric acid  potassium sulphate solution + water (9) silver nitrate solution + sodium iodide solution  precipitate of silver iodide + solution of sodium nitrate (10) solid sodium carbonate + hydrochloric acid  sodium chloride solution + carbon dioxide gas + water.

8. The End

9. IONIC EQUATIONS During a chemical reaction some of these ions may NOT be changed Ionic compounds dissolved in water, exist as separate ions  called spectator ions In an “ionic equation”, spectator ions are OMITTED NaCl(s) + aq  Na + (aq) + Cl - (aq)

10. eg1 Na + OH - (aq) + H + Cl - (aq)  Na + Cl - (aq) + H 2 O (l) Na + and Cl - ions are spectator ions Ionic equation: OH - (aq) + H + (aq)  H 2 O (l) eg2 Cu 2+ SO 4 2- (aq) + Zn (s)  Zn 2+ SO 4 2- (aq) + Cu (s) SO 4 2- ions are spectators Ionic equation: Cu 2+ (aq) + Zn (s)  Zn 2+ (aq) + Cu (s) eg3 2K + Br - (aq) + Cl 2(aq)  2K + Cl - (aq) + Br 2(aq) K + ions are spectators Ionic equation: 2Br - (aq) + Cl 2(aq)  2Cl - (aq) + Br 2(aq)

11. Write full equations for each of the following reactions and then remove the spectator ions to form the ionic equation. (1) Silver nitrate and potassium chloride solutions reacting to form a precipitate of silver chloride and potassium chloride solution (2) Dilute nitric acid (HNO 3 = H + + NO 3 - ) reacting with potassium hydroxide solution to form potassium nitrate solution and water (3)Zinc metal reacting with dilute hydrochloric acid (HCl = H + + Cl - ) to form zinc chloride solution and hydrogen gas. (4) Magnesium metal reacting with copper(II) chloride solution to produce magnesium chloride solution and copper metal