1. Balancing Chemical Reactions

2. Balanced Chemical Equation Atoms can’t be created or destroyed (All the atoms we start with we must end up with) A balanced equation has the same number of each element on both sides of the equation.

3. This equation is already balanced What if it isn’t? C + O O  C O O C + O 2  CO 2

4. We need one more oxygen in the products. C + O  C O O C + O 2  CO O Can’t change the formula, because it describes what it is (carbon monoxide in this example) CO 2

5. We need one more oxygen so we make another CO C + O  C O O O C But where did the other C come from? C

6. 2 C + O 2  2 CO C + O  C O O O C C

7. 1) H 2 + O 2 H 2 O

8. 2) Na + O 2 Na 2 O 2

9. 3) Mg + O 2 MgO

10. 4) N 2 + H 2 NH 3

11. 5) C + S 8 CS 2

12. 6) AgNO 3 + Cu Cu(NO 3 ) 2 + Ag

13. Rules for balancing:  Assemble, 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) - save H and O until LAST!  Check to make sure it is balanced.

14. Never change a subscript to balance an equation. – 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.

15. Whiteboard Practice

16. 7) Na + O 2 Na 2 O

17. 8) N 2 + O 2 N 2 O 5

18. 9) Cs + N 2 Cs 3 N

19. 10) Al + S 8 Al 2 S 3