1. Unit 3: Chemical Equations and Stoichiometry
Balancing Equations

2. Balancing Equations reactants  products
Remember the law of conservation of mass?
When a chemical reaction occurs, no atoms are created or just destroyed – they are just rearranged
amount of each element on the left side (reactants) must equal the amount of the same element on the right side (products)
reactants  products

3. Balancing Equations – The Steps!
Write the unbalanced equation
Ionic compounds: charges must add to zero
Covalent compounds: use prefixes
HOFBrINCl elements are diatomic when alone Example: hydrogen gas is written H2
Add phase if given:
Solid = (s)
Gas = (g)
Liquid = (l)
Aqueous (dissolved in water or solution) = (aq)

4. Balancing Equations Practice #1
Write and balance the following chemical equation:
Lead (IV) sulfide solid + oxygen gas 
lead (IV) oxide solid + sulfur dioxide gas

5. Balancing Equations – The Steps!
Put coefficients in front of each substance to get the quantities on the left side = the right side
Use the smallest whole number coefficients possible.

6. Balancing Equations - Hints
Save “singletons” for last (elements that are not bonded with other elements)
Save oxygen for last (if there are no singletons)
Save hydrogen for 2nd to last

7. Balancing Equations Example #1
Now let’s balance this equation…
__PbS2 (s) + __O2 (g)  __ PbO2 (s) + __SO2 (g)

8. Balancing Equations Check-in
Write and balance the following chemical equation:
iron metal + oxygen gas  iron (III) oxide solid

9. Balancing Equations Practice #2
Write and balance the following chemical equation:
ammonium phosphate soln. + magnesium nitrate soln.  ammonium nitrate soln. + magnesium phosphate solid