1. Chemical Equations and Reactions Balancing Chemical Equations

2. Balancing Equations 1. ONLY add/change Coefficients- NEVER subscripts!!! 2. balance polyatomic ions first (sometimes they can stay grouped) 3. Then balance atoms that appear only once 4. balance H and O last 5. simplify if you can 1. You must be able to simplify ALL the coefficients 6. Check at end! Are both sides equal?

3. Balancing Equations There are multiple methods of balancing. Choose the method that works best for YOU. 1. Free Hand 2. Tic-tac-toe chart 3. Table form (this is the one I prefer)

4. Example 1  Description: Zinc metal is added to hydrochloric acid to create zinc chloride and hydrogen gas.  Word Equation: zinc + hydrochloric acid  zinc chloride + hydrogen  Formula Equation: Zn (s) + HCl(aq)  ZnCl 2 (aq) + H 2 (g)  Balanced Formula Equation 1 Zn (s) + 2 HCl(aq)  1 ZnCl 2 (aq) + 1 H 2 (g)

5. Example 2  Solid calcium metal reacts with water to form aqueous calcium hydroxide and hydrogen gas.  calcium + water  calcium hydroxide + hydrogen  Ca(s) + H 2 O(l)  Ca(OH) 2 (aq) + H 2 (g)  1 Ca(s) + 2 H 2 O(l)  1 Ca(OH) 2 (aq) + 1 H 2 (g)

6. Example 3  Hydrogen peroxide in an aqueous solution decomposes to produce oxygen and water  hydrogen peroxide  oxygen + water  H 2 O 2 (aq)  O 2 (g) + H 2 O(l)  2 H 2 O 2 (aq)  1 O 2 (g) + 2 H 2 O(l)

7. Example 4  Solid copper metal reacts with aqueous silver nitrate to produce solid silver metal and aqueous copper (II) nitrate  copper + silver nitrate  silver + copper (II) nitrate  Cu(s) + AgNO 3 (aq)  Ag(s) + Cu(NO 3 ) 2 (aq)  1 Cu(s) + 2 AgNO 3 (aq)  2 Ag(s) + 1 Cu(NO 3 ) 2 (aq)

8. Example 5  solid zinc metal reacts with aqueous copper (II) sulfate to produce solid copper metal and aqueous zinc sulfate  zinc + copper (II) sulfate  copper + zinc sulfate  Zn(s) + CuSO 4 (aq)  Cu(s) + ZnSO 4 (aq)  ALREADY BALANCED