1 Chapter 7 Chemical Reactions 7.3 Balancing a Chemical Equation Copyright © 2008 by Pearson Education, Inc. Publishing as Benjamin Cummings

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

3 STEP 1 Write the equation with the correct formulas. NH 3 (g) + O 2 (g) NO(g) + H 2 O(g) STEP 2 Determine if the equation is balanced. No, not all atoms are balanced. STEP 3 Balance with coefficients in front of formulas. 4NH 3 (g) + 5O 2 (g) 4NO(g) + 6H 2 O(g) STEP 4 Check that atoms of each element are equal in reactants and products. 4 N (4 x 1N) = 4 N (4 x 1N) 12 H (4 x 3H) = 12 H (6 x 2H) 10 O (5 x 2O) = 10 O(4O + 6O) Balancing Chemical Equations

4 To balance the following equation, Fe 3 O 4 (s) + H 2 (g) Fe(s) + H 2 O(l) Work on one element at a time. Use only coefficients in front of formulas. Do not change any subscripts. Fe:Fe 3 O 4 (s) + H 2 (g) 3Fe(s) + H 2 O(l) O:Fe 3 O 4 (s) + H 2 (g) 3Fe(s) + 4H 2 O(l) H: Fe 3 O 4 (s) + 4H 2 (g) 3Fe(s) + 4H 2 O(l) Steps in Balancing an Equation

5 Check the balance of atoms in the following: Fe 3 O 4 (s) + 4H 2 (g) 3Fe(s) + 4H 2 O(l) A. Number of H atoms in products. 1) 22) 43) 8 B. Number of O atoms in reactants. 1) 22) 43) 8 C. Number of Fe atoms in reactants. 1) 12) 33) 4 Learning Check

6 Fe 3 O 4 (s) + 4H 2 (g) 3Fe(s) + 4H 2 O(l) A. Number of H atoms in products. 3) 8 (4H 2 O) B. Number of O atoms in reactants. 2) 4 (Fe 3 O 4 ) C. Number of Fe atoms in reactants. 2) 3 (Fe 3 O 4 ) Solution

7 Equation for A Chemical Reaction Copyright © 2008 by Pearson Education, Inc. Publishing as Benjamin Cummings

8 Checking a Balanced Equation ReactantsProducts 1 C atom=1 C atom 4 H atoms=4 H atoms 4 O atoms = 4 O atoms Copyright © 2008 by Pearson Education, Inc. Publishing as Benjamin Cummings

9 Balance each equation and list the coefficients in the balanced equation going from reactants to products: A. __Mg(s) + __N 2 (g)__Mg 3 N 2 (s) 1) 1, 3, 2 2) 3, 1, 2 3) 3, 1, 1 B. __Al(s) + __Cl 2 (g) __AlCl 3 (s) 1) 3, 3, 22) 1, 3, 1 3) 2, 3, 2 Learning Check

10 A. 3) 3, 1, 1 3Mg(s) + 1N 2 (g) 1Mg 3 N 2 (s) B. 3) 2, 3, 2 2Al(s) + 3Cl 2 (g) 2AlCl 3 (s) Solution

11 Equations with Polyatomic Ions Copyright © 2008 by Pearson Education, Inc. Publishing as Benjamin Cummings

12 Balancing with Polyatomic Ions MgCl 2 (aq) + Na 3 PO 4 (aq) NaCl(aq) + Mg 3 (PO 4 ) 2 (s) Balance PO 4 3- as a unit MgCl 2 (aq) + 2Na 3 PO 4 (aq) NaCl(aq) + Mg 3 (PO 4 ) 2 (s) 2PO 4 3- = 2PO 4 3- Balance Mg and Cl 3MgCl 2 (aq) + 2Na 3 PO 4 (aq) 6NaCl(aq) + Mg 3 (PO 4 ) 2 (s) 3 Mg 2+ = 3 Mg 2+ 6 Na + = 6 Na + 6 Cl - = 6 Cl -

13 Balance and list the coefficients from reactants to products: A. __Fe 2 O 3 (s) + __C(s) __Fe(s) + __CO 2 (g) 1) 2, 3, 2,3 2) 2, 3, 4, 3 3) 1, 1, 2, 3 B. __Al(s) + __FeO(s) __Fe(s) + __Al 2 O 3 (s) 1) 2, 3, 3, 1 2) 2, 1, 1, 1 3) 3, 3, 3, 1 C. __Al(s) + __H 2 SO 4 (aq) __Al 2 (SO 4 ) 3 (aq) + __H 2 (g) 1) 3, 2, 1, 2 2) 2, 3, 1, 3 3) 2, 3, 2, 3 Learning Check

14 A. 2) 2, 3, 4, 3 2Fe 2 O 3 (s) + 3C(s) 4Fe(s) + 3CO 2 (g) B. 1) 2, 3, 3, 1 2Al(s) + 3FeO(s) 3Fe(s) + 1Al 2 O 3 (s) C. 2) 2, 3, 1, 3 2Al(s) + 3H 2 SO 4 (aq) 1Al 2 (SO 4 ) 3 (aq) + 3H 2 (g) Solution