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 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!
Put coefficients in front of each substance to get the quantities on the left side = the right side
2Na + Cl2  2NaCl
Use the smallest whole number coefficients possible.

4. Balancing Equations - Hints
Start with one of each reactant and product.
Save hydrogen for 2nd to last.
Save oxygen for last.
Diatomic elements: HOFBrINCl (only when alone) Example: hydrogen gas is written H2
Phases:
Solid = (s)
Liquid = (l)
Gas = (g)
Aqueous (dissolved in water or solution) = (aq)

5. Balancing Equations Example #1
Now let’s balance this equation…
__C3H8 (g) + __O2 (g)  __CO2 (g) + __H2O (l)

6. Balancing Equations Practice #1
Balance the following chemical equation:
__PbS2 (s) + __O2 (g)  __PbO2 (s) + __SO2 (g)