1 Chapter 5 Chemical Reactions 5.9a The Mole Relationships in Chemical Equations

2 Law of Conservation of Mass and Stoichiometry The Law of Conservation of Mass indicates that in an ordinary chemical reaction, Matter cannot be created nor destroyed. No change in total mass occurs in a reaction. Mass of products is equal to mass of reactants. Stoichiometry is the study of mass relationships in chemical reactions.

3 Conservation of Mass 2 moles Ag + 1 moles S = 1 mole Ag 2 S 2 (107.9 g) + 1(32.1 g) = 1 (247.9 g) g reactants = g product

4 Consider the following equation: 4 Fe(s) + 3 O 2 (g) 2 Fe 2 O 3 (s) This equation can be read in “moles” by placing the word “moles” between each coefficient and formula. 4 moles Fe + 3 moles O 2 2 moles Fe 2 O 3 Reading Equations In Moles

5 A mole-mole factor is a ratio of the moles for any two substances in an equation. 4Fe(s) + 3O 2 (g) 2Fe 2 O 3 (s) Fe and O 2 4 moles Fe and 3 moles O 2 3 moles O 2 4 moles Fe Fe and Fe 2 O 3 4 moles Fe and 2 moles Fe 2 O 3 2 moles Fe 2 O 3 4 moles Fe O 2 and Fe 2 O 3 3 moles O 2 and 2 moles Fe 2 O 3 2 moles Fe 2 O 3 3 moles O 2 Writing Mole-Mole Factors

6 Consider the following equation: 3 H 2 (g) + N 2 (g) 2 NH 3 (g) A. A mole-mole factor for H 2 and N 2 is 1) 3 moles N 2 2) 1 mole N 2 3) 1 mole N 2 1 mole H 2 3 moles H 2 2 moles H 2 B. A mole-mole factor for NH 3 and H 2 is 1) 1 mole H 2 2) 2 moles NH 3 3) 3 moles N 2 2 moles NH 3 3 moles H 2 2 moles NH 3 Learning Check

7 3H 2 (g) + N 2 (g) 2NH 3 (g) A. A mole-mole factor for H 2 and N 2 is 2) 1 mole N 2 3 moles H 2 B. A mole-mole factor for NH 3 and H 2 is 2) 2 moles NH 3 3 moles H 2 Solution

8 How many moles of Fe 2 O 3 can form from 6.0 mole O 2 ? 4Fe(s) + 3O 2 (g) 2Fe 2 O 3 (s) Relationship:3 mole O 2 = 2 mole Fe 2 O 3 Write a mole-mole factor to determine the moles of Fe 2 O mole O 2 x 2 mole Fe 2 O 3 = 4.0 mole Fe 2 O 3 3 mole O 2 Calculations with Mole Factors

9 Guide to Using Mole Factors

10 How many moles of Fe are needed for the reaction of 12.0 moles O 2 ? 4 Fe(s) + 3 O 2 (g) 2 Fe 2 O 3 (s) 1) 3.00 moles Fe 2) 9.00 moles Fe 3) 16.0 moles Fe Learning Check

11 3) 16.0 moles Fe 12.0 moles O 2 x 4 moles Fe = 16.0 moles Fe 3 moles O 2 Solution