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

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

WHAT’S WRONG HERE!? Ex. burning methane releases carbon dioxide and water CH4 + O2  H2O + CO2 LS RS H 4 2 C 1 1 O 2 3

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

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

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