1. 6.3 and 6.4 Conserving Mass in Chemical Reactions and Balancing Chemical Equations

2. Law of Conservation of Mass
In a chemical reaction, the total mass of the reactants is always equal to the total mass of the products.
Ex. burning methane releases carbon dioxide and water
CH4 + O2  H2O + CO2
25g + 35g  22g + 38g

3. WHAT’S WRONG HERE!?
Ex. burning methane releases carbon dioxide and water
CH4 + O2  H2O + CO2
LS RS H C O

4. Fixing the numbers of atoms
Ex. burning methane releases carbon dioxide and water
CH4 + 2O2  2H2O + CO2
25g + 35g  22g + 38g
LS RS
H 4 4
C 1 1
O 4 4

5. Balancing Chemical Equations
The total number or quantity of each kind of atom is the same before and after a chemical reaction; the atoms are simply rearranged to form new products.
CH4 + 2O2  2H2O + CO2
Use coefficients in front of the skeleton equation to balance the number of atoms in each. LEFT SIDE MUST EQUAL RIGHT SIDE

6. Balancing Chemical Equations
Skeleton Equation: contains the chemical formula of both the reactants & the products but it is not balanced in terms of the number of atoms
CH4 + O2  H2O + CO2
Balanced equation: Number of atoms in reactants and products are equal
CH4 + 2O2  2H2O + CO2