1. Unit: Chemical Reactions Balancing chemical equations

2. After today you will be able to… Explain the Law of Conservation of Mass Balance equations using the “tally method”

3. Law of Conservation of Mass: The mass of your products must be equal to the mass of your reactants. For us, that means there must be the same number of each type of atom before the reaction as after the reaction.

4. Coefficients: Are numbers that go in front of each substance to indicate the number of atoms or molecules that are reacting or being produced.

5. Let’s try some examples! We will be using the “tally method” to balance equations in this class.

6. Examples: Balance the following equation: ___ Al + ___S  ___Al 2 S 3 Al S 1 1 2 3 2 2 3 3 If the numbers match on either side… You’re balanced!

7. Examples: Balance the following equation: ___ Li + ___O 2  ___Li 2 O Li O 1 2 2 1 2 2 2 2 4 4 4

8. Examples: Balance the following equation: ___Fe 2 (SO 4 ) 3 + ___Na 3 (PO 4 )  ___Fe(PO 4 ) + ___Na 2 (SO 4 ) Fe (SO 4 ) 2 3 2 2 Na (PO 4 ) 3 3 1 1 1 2 1 2 2 3 6 2 6 Are we balanced? YES!!!! Helpful tip: Do not separate polyatomic ions!

9. Time to put it all together!

10. Examples: Write the corresponding formula equation and balance. magnesium chlorate  magnesium chloride + oxygen ___Mg(ClO 3 ) 2  ___MgCl 2 + ___O 2 Mg Cl 2 1 O Mg +2 (ClO 3 ) -1 Mg +2 Cl -1 6 2 1 26 3

11. Examples: Write the corresponding formula equation and balance. Potassium + chromium (III)  potassium + chromium (III) ___K 2 (CO 3 ) + ___Cr(NO 3 ) 3  ___K(NO 3 ) + ___Cr 2 (CO 3 ) 3 K (CO 3 ) 1 2 2 carbonate nitrate nitrate carbonate Cr (NO 3 ) K +1 (CO 3 ) -2 Cr +3 (NO 3 ) -1 K +1 (NO 3 ) -1 Cr +3 (CO 3 ) -2 1 3 3 1 2 1 2 2 3 3 6 2 2 6 6 6 6