1 Chapter 12 Stoichiometry 12.1 The Arithmetic of Equations Copyright © 2008 by Pearson Education, Inc. Publishing as Benjamin Cummings

2 In an ordinary chemical reaction, Matter cannot be created nor destroyed. The number of atoms of each element are equal. The mass of reactants equals the mass of products. H 2 (g) + Cl 2 (g) 2HCl(g) 2 mol H (1mol H2), 2 mol Cl (1mol Cl2) = 2 mol H, 2 mol Cl (2mol HCl) 2(1.008) + 2(35.45) = 2(36.46) g = g Law of Conservation of Mass

3 4NH 3 (g) + 5O 2 (g) 4NO(g) + 6H 2 O(g) four molecules NH 3 react with five molecules O 2 to produce four molecules NO and six molecules H 2 O and four mol NH 3 react with five mol O 2 to produce four mol NO and six mol H 2 O Quantities in A Chemical Reaction

4 Balance each equation. Write down the quantities (MOLES) of reactants and products: 1. Na + MgF2 →→NaF + Mg 2. Mg + HCl → MgCl2 + H2 3. Cl2 + KI → KCl + I2 4. NaCl→ Na + Cl2 5. Na + O2 → Na2O 6. Na + HCl → H2 + NaCl

5 Conservation of Mass 2 mol Ag + 1 mol S = 1 mol Ag 2 S 2 (107.9 g) + 1(32.07 g) = 1 (247.9 g) g reactants = g product Copyright © 2008 by Pearson Education, Inc. Publishing as Benjamin Cummings

6 Balance each equation. Calculate the masses of reactants and products: 1. Na + MgF2 →→NaF + Mg 2. Mg + HCl → MgCl2 + H2 3. Cl2 + KI → KCl + I2 4. NaCl→ Na + Cl2 5. Na + O2 → Na2O 6. Na + HCl → H2 + NaCl

7 The equation can be read in “moles” by placing the word “mole” or “mol” after each coefficient. 4Fe(s) + 3O 2 (g) 2Fe 2 O 3 (s) 4 mol Fe + 3 mol O 2 2 mol Fe 2 O 3 Moles in Equations

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

9 Balance each equation. Write down the mole factors possible: 1. Na + MgF2 →→NaF + Mg 2. Mg + HCl → MgCl2 + H2 3. Cl2 + KI → KCl + I2

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

11 3H 2 (g) + N 2 (g) 2NH 3 (g) A. A mole factor for H 2 and N 2 is 2) 1 mol N 2 3 mol H 2 B. A mole factor for NH 3 and H 2 is 2) 2 mol NH 3 3 mol H 2 Solution

12 Copyright © 2008 by Pearson Education, Inc. Publishing as Benjamin Cummings

13 How many moles of Fe 2 O 3 can form from 6.0 mol O 2 ? 4Fe(s) + 3O 2 (g) 2Fe 2 O 3 (s) STEP 1 Given 6.0 mol O 2 Need: moles of Fe 2 O 3. STEP 2 moles O 2 moles Fe 2 O 3 STEP 3 3 mol O 2 = 2 mol Fe 2 O 3 3 mol O 2 and 2 mol Fe 2 O 3 2 mol Fe 2 O 3 3 mol O 2 STEP 4 Set up problem using the mol factor. 6.0 mol O 2 x 2 mol Fe 2 O 3 = 4.0 mol Fe 2 O 3 3 mol O 2 Calculations with Mole Factors

14 How many moles of Fe are needed to react with 12.0 mol O 2 ? 4Fe(s) + 3O 2 (g) 2 Fe 2 O 3 (s) 1) 3.00 mol Fe 2) 9.00 mol Fe 3) 16.0 mol Fe Learning Check

15 3) 16.0 mol Fe Consider the following reaction: 4Fe(s) + 3O 2 (g) 2 Fe 2 O 3 (s) How many moles of Fe are needed to react with 12.0 mol O 2 ? 12.0 mol O 2 x 4 mol Fe = 16.0 mol Fe 3 mol O 2 Solution

16 Calculations with mole factors: 1. How many moles of Na are needed for 4 moles Mg? Na + MgF2 →→NaF + Mg 2. How many moles of HCl are needed for 2.5 moles of H2? Mg + HCl → MgCl2 + H2 3. How many moles of KCl are formed from 5.8 moles KI? Cl2 + KI → KCl + I2 4. How many moles of Na and Cl2 are formed when 6.5 moles NaCl decomposes? NaCl→ Na + Cl2 5. How many moles of Na and O2 need to react in order to form 11 moles Na2O? Na + O2 → Na2O