11.1 Defining Stoichiometry Ashley Lardizabal Discovery School Ch 11 Stoichiometry 11.1 Defining Stoichiometry Ashley Lardizabal Discovery School

OBJECTIVES Identify the quantitative relationships in balanced chemical equation. Determine the mole ratios from a balanced chemical equation.

VOCABULARY & MAIN IDEA Stoichiometry Mole ratio MAIN IDEA: The amount of each reactant present at the start of a chemical reaction determines how much product can form

What is Stoichiometry? Chemical reactions stop when one of the reactants is used up. A chemist needs to know how many grams of a substance A are needed to react completely with a known amount of the other substance B.

Mole-Mass Relationship in Chemical Reactions STOICHIOMETRY is the study of quantitative relations between amounts of reactants used and products formed by a chemical reaction. Based on the law of conservation of mass Antoine Lavoisier Matter cannot be created or destroyed in a chemical reaction

Mole-Mass Relationship in Chemical Reactions Chemical bonds in reactants break and new bonds form to produce product bonds Amount of matter present at the beginning is the same as the amount of matter present at the end. Mass of reactants = Mass of products

Stoichiometry and the balanced chemical equation Reaction of powdered iron and oxygen Iron(III) oxide produced 4Fe(s) + 3O2(g)  2Fe2O3(s) 4 atoms of iron react with 3 molecules of oxygen to produce 2 formula units of iron(III) oxide.

Stoichiometry and the balanced chemical equation Coefficients in an equation represent Individual particles Numbers of moles of particles 4Fe(s) + 3O2(g)  2Fe2O3(s) Also say 4 moles of iron react with 3 moles of oxygen to produce 2 moles of iron(III) oxide.

Stoichiometry and the balanced chemical equation 4Fe(s) + 3O2(g)  2Fe2O3(s) Does the chemical equation tell you anything about the masses of the reactants and products? Not direclty The mass of any substance can be determined by multiplying the number of moles of the substance by the conversion factor that relates mass and number of moles

Stoichiometry and the balanced chemical equation 4Fe(s) + 3O2(g)  2Fe2O3(s) The mass of the reactants can be calculated this way. 4 mole Fe x 55.85 g Fe = 223.4 g Fe 1 mol Fe 3 mol O2 x 32.0 g O2 = 96.00 g O2 1 mol O2 The total mass of the reactants = 319.4 g

Stoichiometry and the balanced chemical equation 4Fe(s) + 3O2(g)  2Fe2O3(s) The mass of the products is 2 mol Fe2O3 x 159.7 g Fe2O3 = 319.4 g 1 mol Fe2O3 Total mass reactants = total mass products Law of Conservation of Mass

Example Problem: Interpreting Chemical Equations The combustion of propane (C3H8) provides energy for heating homes, cooking food, and soldering metal parts. Interpret the equation for the combustion of propane in terms of representative particles, moles, and mass. Show that the law of conservation of mass is observed.

Mole Ratios Use the relationships between coefficients to write conversion factors called mole ratios. MOLE RATIO is a ratio between the number of moles of any two substances in a balanced chemical equations.

Mole Ratios 2Al(s) + 3Br2(l)  2AlBe3(s) Aluminum reacts with bromine to form aluminum bromide Used as a catalyst (speeds up reactions) What mole ratios can be written for this reaction? 6 ratios define all the mole relationships in this equation Each of the 3 substances in the equations forms a ratio with the other 2

Mole Ratios Decomposition of potassium chlorate (KClO3) KClO3(s)  2KCl(s) + 3O2(g) What mole ratios can be written? How many could you write for a reaction involving a total of four reactants and products?

Mole Ratios You need to learn to write mole ratios!!!! Are key to calculations based upon a chemical equation. Suppose you know the amount of one reactant you use in a chemical reaction. With the chemical equation and the mole ratios, you can calculate the amount of any other reactant in the equation and the maximum amount of product you can obtain.

Homework ICN P 219: Reading Check (2) P 371 #1-2 P 372 #3-10