What is stoichiometry Chapter 12.1

Vocabulary Word stoichiometery: the study of quantitative relationships btwn the amounts of reactants and products formed in a chemical rxn.

Stoichiometry Chemists need to know how much of each reactant is needed to optimize a reaction. The law of the conservation of mass says the total mass of the reactants = the total mass of the products. Balanced chemical equations and molar masses let us calculate the masses of the reactants and products in a chemical reaction.

Example Fe+ O 2  Fe 2 O 3 Balanced equation: 4 Fe+ 3 O 2  2 Fe 2 O 3 4 moles of iron + 3 moles oxygen form 2 moles iron oxide

Example 4 moles of iron + 3 moles oxygen form 2 moles iron oxide 4 (55.85) + 3(32) = 2 [ 2 (55.85) + 3 (16)] = = 2( ) = the mass of the reactants = the mass of the products

Vocabulary Word mole ratios: ratios btwn # moles of any 2 substances in a balanced chemical equation.

Mole Ratios 2 Al+ 3 Br 2  2 AlBr 3 ratios: 2 moles Al2 moles Al3 moles Br 2 3 moles Br 2 2 moles AlBr 3 2 moles AlBr 3 the inverse of each ratio is also true 6 ratios can be formed

Mole Ratios To determine the number of ratios that can be formed: # species (different things) x next lowest # 3 species forms 3 x 2 = 6 ratios 4 species forms 4 x 3 = 12 ratios These ratios allow us to determine the amount of reactants and to predict the amount of product formed.