Chapter 9 - Stoichiometry 9-1 Introduction to Stoichiometry Composition Stoichiometry - deals with mass relationships of elements in compounds Reaction Stoichiometry - Involves mass relationships between reactants and products in a chemical reaction I. Reaction Stoichiometry Problems A. Four problem Types, One Common Solution given mass ? given moles ? unknown moles ? unknown mass 1. Given and unknown quantities are in moles 2. Given is an amount in moles and the unknown is a mass (usually in grams) 3. Given is a mass in grams and the unknown is an amount in moles 4. Given is a mass in grams and the unknown is a mass in grams B. Mole Ratio 1. A conversion factor that relates the amounts in moles of any two substances involved in a chemical reaction