Chapter 11: Stoichiometry Section 1: Defining Stoichiometry

Particle and Mole Relationships The study of quantitative relationships between the amounts of reactants used and amounts of products formed by a chemical reaction is called stoichiometry. Based on the Law of Conservation of Mass…matter is neither created nor destroyed in a chemical reaction. Mass of reactants = Mass of products

Stoichiometry Relationships Derived From a Balanced Chemical Equation 4Fe(s) + 3O2(g)  2Fe2O3(s) Iron + Oxygen  Iron (III) Oxide 4 atoms of Fe + 3 molecules O2  2 molecules Fe2O3 4 moles Fe + 3 moles O2  2 moles Fe2O3 223.4g Fe + 96.00g O2  319.4g Fe2O3 319.4g reactants  319.4 g products

Mole Ratios The coefficients in a balanced chemical reaction indicate the relationships between moles of reactants and products. We can use this information to derive conversion factors called mole ratios. A mole ratio is a ratio between the number of moles of any two substances in a balanced chemical reaction.

Mole Ratios 2K(s) + Br2(l)  2KBr(s)

Chapter 11 Section 3 Limiting Reactants

Limiting and Excess Reactants The limiting reactant in the reaction limits the extent of the reaction and thereby determines the amount of product formed. A portion of all the other reactants remain after the reaction stops. Reactants left over when the reaction stops are excess reactants.

Determining the Limiting Reactant These problems are very similar to stoichiometry problems…they follow the same steps. In this case, you will be given two starting amounts and have to determine which reactant is limiting.

Example 1 If 200.0 g of sulfurs reacts with 100.0 g of chlorine, what mass of disulfide dichloride is formed? S8(l) + 4Cl2(g)  4S2Cl2(l)

Example 2 Determine the mass of P4O10 formed if 25.0 g of P4 and 50.0 g of O2 are combined. P4(s) + 5O2(g)  P4O10(s)