Chapter 9A Notes Stoichiometry West Valley High School General Chemistry Mr. Mata

Standard 3e Students will know how to calculate the mole or mass of a reactant or product from the mole or mass of one of the reactants or products.

Essential Question How is stoichiometry used to relate reactants & products in a chemical reaction?

Stoichiometry Stoicheion = g. “element” Metron = g. “measure” Stoichiometry = “to measure the elements”. Stoichiometry - calculation of quantities of substances involved in chemical reactions. Use coefficients of balanced chemical equations to show ratio of moles of reactants & products:

Two Types of Stoichiometry Composition stoichiometry – mass relationships of elements in compounds. Reaction stoichiometry – mass relationships between reactants and products in a chemical reaction. Based on chemical equations and the Law of Conservation of Mass.

Steps to Stoichiometry Start with a balanced chemical equation. Use number of moles of reactants & products. Two types of stoichiometry problems: Mole A -> mole B Gram A -> mole A -> mole B -> gram B

What does this equation mean? N2 + 3H2 2NH3 1 mole of nitrogen (N2) reacts with 3 moles of hydrogen (H2) to form: 2 moles of ammonia (NH3)

N2 + 3H2 2NH3 Mole ratios: 1 mol N2 3 mol H2 3 mol H2 1 mol N2 or 2 mol NH3 1 mol N2 1 mol N2 2 mol NH3 or 2 mol NH3 3 mol H2 3 mol H2 2 mol NH3 or

Mole-Mole Calculations Steps: 1. Write the balanced chemical equation. 2. Write moles of given reactant/product. 3. Multiply by the mole ratio: given mol A x mol B = ___ mol B mol A

N2 + 3H2 2NH3 3 mol H2 = 2 mol NH3 (mol : mol ratio) Calculate the moles of NH3 that can be produced from 10.8 moles of H2. 3 mol H2 = 2 mol NH3 (mol : mol ratio) 10.8 mol H2 x 2 mol NH3 = 3 mol H2 = 7.2 mol NH3

N2 + 3H2 2NH3 25 mol N2 x 2 mol NH3 = 1 mol N2 = 50 mol NH3 Calculate the moles of NH3 that can be produced from 25 moles of N2. 1 mol N2 = 2 mol NH3 (mol : mol ratio) 25 mol N2 x 2 mol NH3 = 1 mol N2 = 50 mol NH3

N2 + 3H2 2NH3 3 mol H2 = 2 mol NH3 (mole : mole ratio) Calculate the moles of NH3 that can be produced from 53.7 moles of H2. 3 mol H2 = 2 mol NH3 (mole : mole ratio) 53.7 mol H2 x 2 mol NH3 = 3 mol H2 = 35.8 mol NH3

Mole: Mole Problem __ Al2O3 -> __ Al + __ O2 Calculate the moles of Al that can be produced from 20 moles of Al2O3. __ mol Al = __ mol Al2O3 (mol : mol ratio) ___ mol Al2O3 x mol Al = mol Al2O3

Solution: 2 Al2O3 -> 4 Al + 3 O2 Calculate the moles of Al that can be produced from 20 moles of Al2O3. 4 mol Al = 2 mol Al2O3 (mol : mol ratio) 20 mol Al2O3 x 4 mol Al = 2 mol Al2O3 40 mol Al