Chemical Equation A shorthand way of reporting details of a chemical reaction Reactants The starting substances in a reaction Placed on the left side of the equation Products The substances formed during a chemical reaction Placed on the right side of the equation Arrow is read as yields Episode 604

Coefficients 2 Used to balance equation Represent the number of molecules, formula units, or atoms of the substances. Law of Conservation of Mass Mass cannot be created or destroyed. Zn + HCl → ZnCl2 + H2 http://www.youtube.com/watch?v=x9iZq3ZxbO8&feature=related 2 Episode 604

Cannot add or change subscripts H2 + O2 → H2O Cannot add or change subscripts Draw boxes C3H8 + O2 → CO2 + H2O 2 2 2 5 3 4 C = 3 C = 1 3 H = 8 H = 2 8 O = 2 10 O = 3 7 10 Episode 604

Guidelines for Balancing Equations Start by making an element inventory Draw boxes around each formula in the equation Begin with one molecule or formula unit of the substance containing the most atoms Balance polyatomic ions that appear on both sides of the equation as a single unit Appears in a reactant and a product Balance hydrogen and oxygen atoms last Episode 604

Cu + AgNO3 → Cu(NO3)2 + Ag KNO3 → KNO2 + O2 Polyatomic Ions? 2 2 Cu + AgNO3 → Cu(NO3)2 + Ag KNO3 → KNO2 + O2 Cu = 1 Cu = 1 Ag = 1 2 Ag = 1 2 NO3 = 1 2 NO3 = 2 2 2 2 K = 1 2 K = 1 N = 1 2 N = 1 2 O = 3 6 O = 4 6 Episode 604

Hydrogen and oxygen combine to produce water H + O → H2O Reasonable…? But, wrong H2 + O2 → H2O 7 Diatomic Elements Diatomic: two elements Hydrogen, nitrogen, oxygen, fluorine, chlorine, bromine, iodine Balance it ! 2 2 Episode 604

CS2 Carbon disulfide reacts with oxygen to produce carbon dioxide and sulfur dioxide. O2 CO2 SO2 Balance it ! CS2 + O2 → CO2 + SO2 3 2 C = 1 C = 1 S = 2 S = 1 2 O = 2 6 O = 4 6 Episode 604