Balancing Chemical Equations

Law of Conservation of Mass To follow the Law of Conservation of Mass, we must have the same number of atoms of each element on both sides of the equation.

Balanced Chemical Equations C + O2  CO2 This is balanced!! 1 C and 2 O on each side of the equation. H2 + O2  H2O This is not balanced!! 2 H’s on both the right and the left of the arrow, but 2O’s on the left and only 1 O on the right.

How to Balance Chemical Equations To balance an equation we change coefficients, but never the subscripts. Coefficient - large numbers in front of the compound. This tells us how many atoms or molecules are taking place in the reaction. H2 + O2  H2O The balanced equation: 2 H2 + O2  2 H2O

Balancing Chemical Equations 1 To balance an equation: 2 Determine your equation. If this part is not correct, your equation will never balance. 3 Create a chemical inventory of the elements then count the atoms. Consider polyatomic ions to be a unit if it is on both sides of the equation – like OH or PO4. 4 Balance the elements one at a time using coefficients. When there is no coefficient, we assume it to be one, just like subscripts. You can NEVER change the subscripts in a chemical equation!!! 5 Check each atom so all are balanced. Equal on each side!!! 6 All the coefficients should be in the lowest possible ratio.

Balancing Chemical Equations Silver nitrate and copper metal combine to form copper (II) nitrate and silver metal. AgNO3 + Cu  Cu(NO3)2 + Ag 1 Ag 1 1 NO3 2 1 Cu 1 Balance by changing coefficients: 2 AgNO3 + __Cu  __Cu(NO3)2 + 2 Ag

Balancing Chemical Equations Carbon monoxide combines with iron (III) oxide to form iron metal and carbon dioxide. CO + Fe2O3  Fe + CO2 1 C 1 2 Fe 1 4 O 2 Balance by changing coefficients: 3 CO + __Fe2O3  2 Fe + 3 CO2