3.7 Chem. Eqs & 3.8 Balancing Chem. Eqs

Transcription

1 3.7 Chem. Eqs & 3.8 Balancing Chem. Eqs

2 Chemical Equations A chemical equation gives the chemical formulas of the reactants on the left of the arrow and the products on the right. Reactants Product C(s) O 2 (g) CO 2 (g) Copyright Houghton Mifflin Company. All rights reserved. 3 2

3 Symbols Used in Equations Symbols used in chemical equations show TABLE the states of the reactants. the states of the products. the reaction conditions. Copyright Houghton Mifflin Company. All rights reserved. 3 3

4 Chemical Equations are Balanced In a balanced chemical reaction atoms are not gained or lost. the number of reactant atoms is equal to the number of product atoms. Copyright Houghton Mifflin Company. All rights reserved. 3 4

5 A Balanced Chemical Equation In a balanced chemical equation, there must be the same number of each type of atom on the reactant side and on the product side of a balanced equation. numbers called coefficients are used in front of one or more formulas. Al + S Al 2 S 3 Not Balanced 2Al + 3S Al 2 S 3 Balanced 2 Al = 2 Al 3 S = 3 S Copyright Houghton Mifflin Company. All rights reserved. 3 5

6 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) 4 PBr 3 (g) B. 2Al(s) + Fe 2 O 3 (s) 2Fe(s) + Al 2 O 3 (s) Copyright Houghton Mifflin Company. All rights reserved. 3 6

7 Solution A. P 4 (s) + 6Br 2 (l) 4 PBr 3 (g) 4 P 4 P 12 Br 12 Br B. 2Al(s) + Fe 2 O 3 (s) 2Fe(s) + Al 2 O 3 (s) 2 Al 2 Al 2 Fe 2 Fe 3 O 3 O Copyright Houghton Mifflin Company. All rights reserved. 3 7

8 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 5 OH(l) Copyright Houghton Mifflin Company. All rights reserved. 3 8

9 Solution Determine if each equation is balanced or not. A. Na(s) + N 2 (g) Na 3 N(s) No. 2 N on reactant side, 1 N on product side. 1 Na on reactant side, 3 Na on product side. B. C 2 H 4 (g) + H 2 O(l) C 2 H 5 OH(l) Yes. 2 C = 2 C 6 H = 6 H 1 O = 1 O Copyright Houghton Mifflin Company. All rights reserved. 3 9

10 Guide to Balancing a Chemical Equation Copyright 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings Copyright Houghton Mifflin Company. All rights reserved. 3 10

11 Steps in Balancing an Equation 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) Copyright Houghton Mifflin Company. All rights reserved. 3 11

12 Balancing Chemical Equations 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, not all atoms are balanced. 3. Balance with coefficients in front of formulas. 4NH 3 (g) + 5O 2 (g) 4NO(g) + 6H 2 O(g) 4. Check that atoms of each element are equal in reactants and products. 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) Copyright Houghton Mifflin Company. All rights reserved. 3 12

13 Equation for A Chemical Reaction Copyright Houghton Mifflin Company. All rights reserved. 3 13

14 Checking a Balanced Equation Reactants Products 1 C atom = 1 C atom 4 H atoms = 4 H atoms 4 O atoms = 4 O atoms Copyright Houghton Mifflin Company. All rights reserved. 3 14

15 Learning Check 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) 2 2) 4 3) 8 B. Number of O atoms in reactants. 1) 2 2) 4 3) 8 C. Number of Fe atoms in reactants. 1) 1 2) 3 3) 4 Copyright Houghton Mifflin Company. All rights reserved. 3 15

16 Solution 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 ) Copyright Houghton Mifflin Company. All rights reserved. 3 16

17 Learning Check 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, 2 2) 1, 3, 1 3) 2, 3, 2 Copyright Houghton Mifflin Company. All rights reserved. 3 17

18 Solution 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) Copyright Houghton Mifflin Company. All rights reserved. 3 18

19 Equations with Polyatomic Ions Copyright Houghton Mifflin Company. All rights reserved. 3 19

20 Balancing with Polyatomic Ions MgCl 2 (aq) + Na 3 PO 4 (aq) NaCl(aq) + Mg 3 (PO 4 ) 2 (s) Balance PO 3-4 as a unit MgCl 2 (aq) + 2Na 3 PO 4 (aq) NaCl(aq) + Mg 3 (PO 4 ) 2 (s) 2 PO 3-4 = 2 PO 3-4 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 - Copyright Houghton Mifflin Company. All rights reserved. 3 20

21 Learning Check 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 Copyright Houghton Mifflin Company. All rights reserved. 3 21

22 Solution 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) Copyright Houghton Mifflin Company. All rights reserved. 3 22