1 Chapter 5 Chemical Quantities and Reactions 5.7 Mole Relationships in Chemical Equations Copyright © 2009 by Pearson Education, Inc.

2 Law of Conservation of Mass The law of conservation of mass indicates that in an ordinary chemical reaction, matter cannot be created or destroyed. no change in total mass occurs in a reaction. mass of products is equal to mass of reactants.

3 Conservation of Mass 2 moles of Ag + 1 mole of S = 1 mole of Ag 2 S 2 (107.9 g) + 1(32.1 g) = 1 (247.9 g) g reactants = g product Copyright © 2009 by Pearson Education, Inc

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 of” between each coefficient and formula. 4 moles of Fe + 3 moles of O 2 2 moles of 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: 3H 2 (g) + N 2 (g) 2NH 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 moles of O 2 ? 4Fe(s) + 3O 2 (g) 2Fe 2 O 3 (s) Relationship: 3 mole O 2 = 2 mole Fe 2 O 3 Use a mole-mole factor to determine the moles of Fe 2 O mole O 2 x 2 mole Fe 2 O 3 = 4.0 moles of Fe 2 O 3 3 mole O 2 Calculations with Mole Factors

9 Guide to Using Mole Factors Copyright © 2009 by Pearson Education, Inc.

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

11 In a problem, identify the compounds given and needed. How many moles of Fe are needed for the reaction of 12.0 moles of O 2 ? 4Fe(s) + 3O 2 (g) 2Fe 2 O 3 (s) The possible mole factors for the solution are 4 moles Fe and3 moles O 2 3 moles O 2 4 moles Fe Study Tip: Mole Factors

12 3) 16.0 moles of Fe 12.0 moles O 2 x 4 moles Fe = 16.0 moles of Fe 3 moles O 2 Solution