Worksheet: Balancing Equations
I. Fill in the blanks with the most appropriate term:
A ________________ ________________ tells the story of a chemical reaction. ________________ are the starting substances in the reaction while ________________ are the new substances that are formed. The large numbers in front of some of the formulas are called ________________. These numbers are used to ________________ the equation because chemical reactions must obey the Law of ________________ of Matter. The number of atoms of each element on both sides of the equation must be ________________ because matter
cannot be ________________ or ________________. When balancing equations, the only numbers that can be changed are ________________; remember that ________________ must never be changed in order to balance an equation.
II. Balance the following equations:
1. Al + O2 Al2O3


2. C3H8 + O2 CO2 + H2O


3. P4 + O2 P2O3




4. KNO3 KNO2 + O2


5. O2 + CS2 CO2 + SO2


6. KClO3 KCl + O2


7. N2 + H2 NH3


8. NaF + Br2 NaBr + F2


9. Al + HCl H +AlCl3


10. WO3 + H2 W + H2O