Chapter 12 Stoichiometry

Stoichiometry The branch of chemistry that deals with the mass relationships of elements in compounds and the mass relationships between reactants and products in a chemical reaction.

Composition Stoichiometry Stoichiometry that deals with the mass relationships of elements in compounds

Reaction Stoichiometry Stoichiometry involving the mass relationships between reactants and products in a chemical reaction

Equations are the recipes that tell chemists what amounts of reactants to mix and what amounts of products to expect. The quantities of reactants and products -----come from the balanced equation.

When you know the quantity (grams or moles) of one substance in a reaction, you can calculate the quantity of any other substance consumed or created in the reaction.

Calculations using balanced equations are called stoichiometric calculations. For chemists, stoichiometry is a form of bookkeeping.

INTERPRETING CHEMICAL EQUATIONS N2(g) + 3H2(g) 2NH3(g) 1 mol of nitrogen reacts with 3 mol of hydrogen -------to form 2 mol of ammonia.

Reaction – Stoichiometry Problems Begin with a balanced chemical equation!!!

Mole-Mole Calculations The coefficients from the balanced equation are used to write conversion factors called mole ratios.

Three of the mole ratios for this equation are 1 mol N2 2 mol NH3 3 mol H2 3 mol H2 1 mol N2 2 mol NH3

Reaction – Stoichiometry Problems Identify the information given Identify the unknown, the information you are expected to find. Given  Unknown

Unknown amount in moles Given amount in moles  Mole to Mole Ratio Unknown amount in moles

Thus a general solution for a mole-mole problem is given by From balanced equation x mol G x = mol W b mol W xb a mol G a Given Mole ratio Calculated

How many moles of ammonia are produced when 0 How many moles of ammonia are produced when 0.60 mol of nitrogen reacts with hydrogen? 2 mol NH3 1 mol N2 0.60 mol N2 x = 1.20 mol NH3 Given Mole Ratio

Problem In a spacecraft, the carbon dioxide exhaled by astronauts can be removed by its reaction with lithium hydroxide. CO2(g) + 2 LiOH(s)  Li2CO3(s) + H2O (l) How many moles of lithium hydroxide are required to react with 20 moles of CO2, the average amount exhaled by a person each day?

Answer 20 mole CO2 x 2 mole LiOH 1 mole CO2 = 40 mole LiOH