Balancing equations View on This!

Learning goals We are learning to apply the law of conservation of mass. We are learning to balance chemical equations.

Recall The law of conservation of mass states that mass cannot be created nor destroyed in a chemical reaction. Chemical equations are written to show all of the reactants and products in a chemical reaction. To be sure the equation does not violate the conservation of mass, we must balance it.

Balancing Chemical Equations Consider the following skeleton equation: Let’s look at the atoms of each element present: Where did the atom of oxygen go? Nowhere! We just need to balance the equation. H2 + O2 H2O # Reactants Atom # Products 2 H 2 2 O 1

To balance an equation we simply add coefficients to our equation so that our RAP sheet is correct: Our balanced chemical equation is: 2 H2 + O2 H2O 2 # Reactants Atom # Products 2 4 H 2 4 2 O 1 2 H2 + O2 H2O 2

Balancing Tips Balance elements of complicated formulas first. Never change a subscript in a compound, only add coefficients. Hydrogen & oxygen will appear very frequently so balance hydrogen second last and oxygen last. You MAY be able to treat polyatomic ions as a group instead of separating them.

Example #2 N2 + H2 NH3 3 2 Balance the chemical equation below: # R Atom # P 2 N 1 2 2 6 H 3 6

Example #3 2 Na + HCl H2 + NaCl 2 2 Balance the chemical equation below: 2 Na + HCl H2 + NaCl 2 2 # R Atom # P 1 2 Na 1 2 1 2 Cl 1 2 1 2 H 2

Copper (I) Oxide + Carbon  Copper + Carbon dioxide Example #4 Given the word equation below, determine the balanced chemical equation. Copper (I) Oxide + Carbon  Copper + Carbon dioxide

2 Cu2O + C 4 2 Cu + CO2 # R Atom # P 2 4 Cu 1 2 4 1 C 1 1 2 O 2

Silver Nitrate + Calcium Chloride  Silver Chloride + Calcium Nitrate Example #5 Given the word equation below, determine the balanced chemical equation. Silver Nitrate + Calcium Chloride  Silver Chloride + Calcium Nitrate

2 AgNO3 + CaCl2 2 AgCl + Ca(NO3)2 # R Atom # P 1 2 NO3 2 1 2 Ag 1 2 1

Learning goals We are learning to apply the law of conservation of mass. We are learning to balance chemical equations.

Homework P.236 #3, 5-7