Balancing Chemical Equations

The Law of Conservation of Mass Rationale for balancing chemical equations Discovered by Antoine Lavoisier “Matter is neither created nor destroyed” French chemist, Antoine Lavoisier circa 1700’s

Coefficient & Subscript The coefficient times the subscript gives the total number of atoms. When no coefficient or subscript is shown, a one is understood.

Examples of Coefficients & Subscripts 2H2 – there are 2 x 2 atoms of hydrogen (a total of 4) 2(NH4)2S – there are 2 x 4 x 2 atoms of hydrogen (a total of 16), and 2 x 1 atoms of sulfur ( a total of 2)

Equations Zn + 2HCl ZnCl2 + H2 (reactant) + (reactant) yields (product) (product) produces equals

Law of Conservation of Mass We must finish our chemical reaction with as many atoms of each element as we started. 2H2+ O2 2H2O The equation above is balanced. It has the same number of each atom (mass) on each side of the arrow.

Steps for Balancing Equations Write out the equation List # of atoms on each side Change the coefficients to balance the equation

Balancing Equations Mg + O2 MgO Mg = 1 Mg = 1 O = 2 O = 1