1. 1 Chapter 5 Chemical Quantities and Reactions 5.4 Chemical Equations Copyright © 2009 by Pearson Education, Inc.

2. 2 Chemical Equations A chemical equation gives the formulas of the reactants on the left of the arrow. the formulas of the products on the right of the arrow. ReactantsProduct C(s) O 2 (g) CO 2 (g) Copyright © 2009 by Pearson Education, Inc.

3. 3 Symbols Used in Equations Symbols in chemical equations show the states of the reactants. the states of the products. the reaction conditions. TABLE

4. 4 Chemical Equations are Balanced In a balanced chemical reaction no atoms are lost or gained. the number of reacting atoms is equal to the number of product atoms. Copyright © 2009 by Pearson Education, Inc.

5. 5 A Balanced Chemical Equation In a balanced chemical equation, the number of each type of atom on the reactant side is equal to the number of each type of atom on the product side. numbers called coefficients are used in front of one or more formulas to balance the number of atoms. Al + S Al 2 S 3 Not Balanced 2Al + 3S Al 2 S 3 Balanced using coefficients 2 Al = 2 Al Equal number of Al atoms 3 S = 3 S Equal number of S atoms

6. 6 A Study Tip: Using Coefficients When balancing a chemical equation, use one or more coefficients to balance atoms. never change the subscripts of any formula. N 2 + O 2 NO Not Balanced N 2 + O 2 N 2 O 2 Incorrect formula N 2 + O 2 2NO Correctly balanced using coefficients

7. 7 Learning Check State the number of atoms of each element on the reactant side and the product side for each of the following balanced equations. A. P 4 (s) + 6Br 2 (l) 4PBr 3 (g) B. 2Al(s) + Fe 2 O 3 (s) 2Fe(s) + Al 2 O 3 (s)

8. 8 Solution A. P 4 (s) + 6Br 2 (l) 4PBr 3 (g) 4 P atoms =4 P atoms 12 Br atoms = 12 Br atoms B. 2Al(s) + Fe 2 O 3 (s) 2Fe(s) + Al 2 O 3 (s) 2 Al atoms =2 Al atoms 2 Fe atoms = 2 Fe atoms 3 O atoms =3 O atoms

9. 9 Learning Check Determine if each equation is balanced or not. A. Na(s) + N 2 (g) Na 3 N(s) B. C 2 H 4 (g) + H 2 O(l) C 2 H 6 O(l)

10. 10 Solution Determine if each equation is balanced or not. A. Na(s) + N 2 (g) Na 3 N(s) No. 2 N atoms on reactant side; only 1 N atom on the product side. 1 Na atom on reactant side; 3 Na atoms on the product side. B. C 2 H 4 (g) + H 2 O(l) C 2 H 6 O(l) Yes. 2 C atoms = 2 C atoms 6 H atoms = 6 H atoms 1 O atom = 1 O atom

11. 11 Guide to Balancing a Chemical Equation

12. 12 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

13. 13 1. Write the equation with the correct formulas. NH 3 (g) + O 2 (g) NO(g) + H 2 O(g) 2. Determine if the equation is balanced. No, H atoms are not balanced. 3. Balance with coefficients in front of formulas. 2NH 3 (g) + O 2 (g) 2NO(g) + 3H 2 O(g) Double the coefficients to give even number of O atoms. 4NH 3 (g) + 7O 2 (g) 4NO(g) + 6H 2 O(g) Balancing Chemical Equations

14. 14 4. Check that atoms of each element are equal in reactants and products. 4NH 3 (g) + 5O 2 (g) 4NO(g) + 6H 2 O(g) 4 N (4 x 1 N) = 4 N (4 x 1 N) 12 H (4 x 3 H) = 12 H (6 x 2 H) 10 O (5 x 2 O)= 10 O(4 O + 6 O) Balancing Chemical Equations

15. 15 Equation for a Chemical Reaction Copyright © 2009 by Pearson Education, Inc.

16. 16 Checking a Balanced Equation ReactantsProducts 1 C atom=1 C atom 4 H atoms=4 H atoms 4 O atoms = 4 O atoms Copyright © 2009 by Pearson Education, Inc.

17. 17 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

18. 18 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

19. 19 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

20. 20 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

21. 21 Equations with Polyatomic Ions 2Na 3 PO 4 (aq) + 3MgCl 2 (aq) Mg 3 ( PO 4 (s) + 6NaCl(aq) Copyright © 2009 by Pearson Education, Inc.

22. 22 Balancing with Polyatomic Ions Na 3 PO 4 (aq) + MgCl 2 (aq) Mg 3 (PO 4 ) 2 (s) + NaCl(aq) Balance PO 4 3- as a unit 2Na 3 PO 4 (aq) + MgCl 2 (aq) Mg 3 (PO 4 ) 2 (s) + NaCl(aq) 2 PO 4 3- = 2 PO 4 3- Check Na + balance 6 Na + = 6 Na + Balance Mg and Cl 2Na 3 PO 4 (aq) + 3MgCl 2 (aq) Mg 3 (PO 4 ) 2 (s) + 6NaCl(aq) 3 Mg 2+ = 3 Mg 2+ 6 Cl - = 6 Cl -

23. 23 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

24. 24 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