1. CHEMISTRY PART 12 Balancing Chemical Equations

2. Counting Atoms  Coefficient:  The number in front to show how many molecules or atoms.  Subscript:  The small number to show how many atoms.  To get the total number of atoms:  multiply the coefficient and the subscript.

3. Counting Atoms  Count the number of atoms in each:  H 2 SO 4  CaCl 2  4NaF  2KNO 3  3K 2 SO 4  2Mg 3 (PO 4 ) 2 AtomNumber Mg6 P4 O16

4. Law of Conservation of Mass  Mass of Reactants = Mass of Products  Reactants:  Undergoes a chemical reaction.  Products:  The result of a chemical reaction.

5. Law of Conservation of Mass  Law of Conservation of Mass Law of Conservation of Mass  The # of atoms of each reactants must equal the # of atoms in the products  Matter cannot be created or destroyed.  Atoms cannot be gained or lost during a chemical reaction.

6. Law of Conservation of Mass A+B→C+DA+B→C+D A+B → AB ReactantsProducts “produces/ gives” “reacts with”

7. Types of Chemical Equations  Word Equation:  words only, no formulas  methane + oxygen → carbon dioxide + water  Skeleton Equation:  formulas, but not balanced  CH 4 + O 2 → CO 2 + H 2 O

8. Types of Chemical Equations  Balanced Equation:  formulas, balanced, and often shows the state of each substance.  CH 4(g) + 2O 2(g) → CO 2(g) + 2H 2 O (l)

9. Balancing Chemical Equations  The skeleton equation needs coefficients to balance both sides.  You CANNOT change the subscripts.  You can only add coefficients.  CH 4(g) + O 2(g) → CO 2(g) + H 2 O (l)  CH 4(g) + 2O 2(g) → CO 2(g) + 2H 2 O (l)

10. Balancing Equations Examples  CH 4(g) + O 2(g) → CO 2(g) + H 2 O (l)  CH 4(g) + 2O 2(g) → CO 2(g) + 2H 2 O (l) CCH H H H O O H O O H H HO O O O When we add 2 H’s here, we automatically now have 4 O’s. To balance, we must add 2 O’s to this side.

11. Balancing Equations Examples  Hg + O 2 → HgO  2Hg + O 2 → 2HgO Hg = 1 O = 2 Hg = 1 O = 1 2 2 2 2 2

12. Balancing Equations Examples  Aluminum reacts with oxygen to form aluminum oxide  Al + O 2 → Al 2 O 3  4Al + 3O 2 → 2Al 2 O 3

13. Balancing Equations Examples  CaO + H 2 O → Ca(OH) 2  Already balanced.  Do not need 1’s.  Do NOT put 0’s.  CaO + H 2 O → Ca(OH) 2

14. Remember  You can only change the coefficients to balance.  You can not have coefficients that are fractions.  Double check to make sure coefficients can’t be reduced.

15. Strategies  Trial and error will work, but can be very inefficient.  Balance compounds first, elements last.  Balance one compound at a time.  Start with an element that appears only once on each side.  If H and O appear, attempt to balance them LAST.  Polyatomic ions can be balanced as a whole group if they appear on both sides.  Always double check after you finish.

16. Practice 1. ___N 2(g) + ___H 2(g) → ___NH 3(g) N 2(g) + 3H 2(g) → 2NH 3(g) 2. ___Fe (s) + ___H 2 SO 4(aq) → ___H 2 + Fe 2 (SO 4 ) 3(aq) 2Fe (s) + 3H 2 SO 4(aq) → 3H 2 + Fe 2 (SO 4 ) 3(aq)

17. Practice 1. Fe + Br 2 → FeBr 3 2. CaCl 2 + Na → NaCl + Ca 3. Sn(NO 2 ) 4 + K 3 PO 4 → KNO 2 + Sn 3 (PO 4 ) 4 4. C 2 H 6 + O 2 → CO 2 + H 2 O

18. Practice  Page 133 # 18

19. Practice 1. sodium + chlorine → sodium chloride 2. iron (II) oxide → iron + oxygen 3. methane + oxygen → carbon dioxide + water 4. copper (I) oxide → copper + oxgyen

20. Practice 1. ___C 10 H 22 + ___O 2 → ___CO 2 + ___H 2 O 2. ___ Fe + ___ O 2 → ___ Fe 2 O 3 3. ___ Al 2 (SO 4 ) 3 + ___NH 4 Br → ___ (NH 4 ) 2 SO 4 + ___ AlBr 3 4. ___ N 2 H 4 → ___ N 2 + ___ H 2 5. ___ HNO 3 + ___ Ba(OH) 2 → ____ Ba(NO 3 ) 2 + ___ H 2 O

21. Practice  Worksheet  Page 133 # 13, 18  Page 137 # 8, 9, 13 – 18  Page 134 # 11 – 13