1. Topic: Names, Formulas, Equations, & Reactions
Aim: How do we balance chemical equations?
Do now: List the number of each element present in the following compound: 3(NH4)3PO4
HW:

2. REACTANTS YIELD PRODUCTS
Chemical Equations
Show which bonds are broken and which bonds are built
# of atoms on left side of arrow MUST equal # of atoms on the right side of arrow
REACTANTS YIELD PRODUCTS
Mg + 2HCl  MgCl2 + H2
1 Mg, 2 H, 2 Cl 1Mg, 2 H, 2 Cl

3. Hint:

4. Examples Unbalanced Equation Balanced Equation Al + O2  Al2O3
1 Al on left Al on right
2 O on left O on right
Balanced Equation
4Al + 3O  Al2O3
4 Al on left Al on right
6 O on left O on right

5. How do we balance equations?
Change the COEFFICIENTS of the formulas until you have the same # of atoms on both sides of arrow
NEVER change a subscript!!
EVER!

6. Balancing Equations __ H2 + __ O2  __ H2O 2 H 2 H 2 O 1 O
Starting #s
2 O
1 O
__ H2 + __ O  H2O
2 H
4 H
Update #s
2 O
2 O
2 H2 + __ O  H2O
4 H
4 H
Update #s
2 O
2 O

7. Balancing Equations __C + __H2  __C3H8 1 C 3 C 8 H 2 H
Starting #s
8 H
2 H
3C + 4H  __C3H8
3 C
3 C
Updated #s
8 H
8 H

8. More Practice. Because I care.
N2 + O2  N2O
K + Br2  KBr

9. Still caring…
Al + HCl  H2 + AlCl3

10. How can one person care so much?
If a polyatomic ion is present in the equation ON BOTH SIDES, keep it together as a unit. (It’s easier to balance.)
BaCl2 + Al2(SO4)3  BaSO4 + AlCl3

11. If you see OH on one side and H2O on the other, rewrite H2O as HOH so you now have an OH on each side.
Al(OH)3 + H2SO4  Al2(SO4) H2O