2. Chemical Reactions

3. Chemical Equations A chemical equation is a representation of a chemical reaction –The formulas of the reactants (on the left) are connected by an arrow with the formulas of the products (on the right). –The reactants turn into the products. Reactants  Products the substances you start with (the ones reacting) the substances you end up with (the ones produced)

4. Skeleton Equation Does not indicate the amounts of reactants or products –No coefficients Example Fe + O 2  Fe 2 O 3

5. Word Equations Chemical formulas are not given Example Methane + Oxygen  Carbon dioxide + Water The arrow means yields, gives, or reacts to produce.

6. Rules for balancing  Write the correct formulas for all the reactants and products  Count the number of atoms of each type appearing on both sides  Balance the elements one at a time by adding coefficients (the numbers in front)  Check to make sure it is balanced.

7. Never Change a subscript to balance an equation If you change the formula you are describing a different reaction –H 2 O is a different compound than H 2 O 2 Never put a coefficient in the middle of a formula –2 NaCl is okay, Na2Cl is not

8. Learning Check: __ H 2 + ___ O 2  ___ H 2 O __ SO 2 + ___ O 2  ___ SO 3

9. Answers 2 H 2 + O 2  2 H 2 O 2 SO 2 + O 2  2 SO 3

10. Try to balance this reaction: __Al(OH) 3 (s) + __H 2 SO 4 (aq)  __Al 2 (SO 4 ) 3 (aq) + __H 2 O(l) Al S H O Al S H O 1 1 5 7 2 3 2 13 12 18 8 236 2 10 3 12 18

11. Balance these equations __ Mg+ __ O 2 → __ MgO __ KClO 3 → __ KCl + __ O 2 __ Cu + __ AgNO 3 → __ Cu(NO 3 ) 2 + __ Ag __KOH + __ H 3 PO 4 → __ K 3 PO 4 + __ H 2 O

12. ANSWERS 2 Mg+ O 2 → 2 MgO 2 KClO 3 → 2 KCl + 3 O 2 Cu + 2 AgNO 3 → Cu(NO 3 ) 2 + 2 Ag 3 KOH + H 3 PO 4 → K 3 PO 4 + 3 H 2 O