Chapter 5 Chemical Quantities and Reactions 5.3 Chemical Changes 1

Physical Change In a physical change, the state, shape, or size of the material changes. the identity and composition of the substance do not change. 2

Chemical Change In a chemical change, reacting substances form new substances with different compositions and properties. a chemical reaction takes place. 3

Some Examples of Chemical and Physical Changes 4

Examples Classify each of the following as a 1) physical change or 2) chemical change. A. ____Burning a candle. B. ____Ice melting on the street. C. ____Toasting a marshmallow. D. ____Cutting a pizza. E. ____Polishing a silver bowl. 5

Chemical Reaction In a chemical reaction a chemical change produces one or more new substances. there is a change in the composition of one or more substances. 6 Copyright © 2009 by Pearson Education, Inc.

Chemical Reaction In a chemical reaction old bonds are broken and new bonds are formed. atoms in the reactants are rearranged to form one or more different substances. 7

Chemical Reaction In a chemical reaction the reactants are Fe and O 2. the new product Fe 2 O 3 is called rust. 8

Chapter 5 Chemical Quantities and Reactions 5.4 Chemical Equations 9

Chemical Equations 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 10 C(s) O 2 (g) CO 2 (g)

Symbols Used in Equations Symbols in chemical equations show the states of the reactants. the states of the products. the reaction conditions. 11 TABLE

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. 12

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 13

A Study Tip: Using Coefficients 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 14

Examples 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) 15

16 Guide to Balancing a Chemical Equation

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) 17

Equation for a Chemical Reaction 18 Copyright © 2009 by Pearson Education, Inc.

Checking a Balanced Equation ReactantsProducts 1 C atom=1 C atom 4 H atoms=4 H atoms 4 O atoms = 4 O atoms 19 Copyright © 2009 by Pearson Education, Inc.

Examples 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 20

Examples 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 21

Equations with Polyatomic Ions 22 2Na 3 PO 4 (aq) + 3MgCl 2 (aq) Mg 3 ( PO 4 (s) + 6NaCl(aq) Copyright © 2009 by Pearson Education, Inc.

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

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) + __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 24

Examples Balance the following chemical equations a. …..S(s) + …. O 2 (g)  …… SO 3 (g) b. …..Al(s) + ….Cl 2 (g)  ……AlCl 3 (s) c. ……Mg(s) + ……AgNO 3 (aq)  …..Mg(NO 3 ) 2 (aq) + …… Ag(s)

Chapter 5 Chemical Quantities and Reactions 5.5 Types of Reactions 26

Type of Reactions Chemical reactions can be classified as combination reactions. decomposition reactions. single replacement reactions. double replacement reactions. 27

Combination In a combination reaction, two or more elements form one product. or simple compounds combine to form one product. + 2Mg(s) + O 2 (g) 2MgO(s) 2Na(s) + Cl 2 (g)2NaCl(s) SO 3 (g) + H 2 O(l)H 2 SO 4 (aq) 28 AB AB

Decomposition In a decomposition reaction, one substance splits into two or more simpler substances. 2HgO(s) 2Hg(l) + O 2 (g) 2KClO 3 (s) 2KCl(s) + 3 O 2 (g) 29

Examples Classify the following reactions as 1) combination or 2) decomposition. ___A. H 2 (g) + Br 2 (g) 2HBr(l) ___B. Al 2 (CO 3 ) 3 (s) Al 2 O 3 (s) + 3CO 2 (g) ___C. 4Al(s) + 3C(s) Al 4 C 3 (s) 30

Single Replacement In a single replacement reaction, one element takes the place of a different element in another reacting compound. Zn(s) + 2HCl(aq) ZnCl 2 (aq) + H 2 (g) Fe(s) + CuSO 4 (aq)FeSO 4 (aq) + Cu(s) 31

Zn and HCl is a Single Replacement Reaction 32

Double Replacement In a double replacement, two elements in the reactants exchange places. AgNO 3 (aq) + NaCl(aq)AgCl(s) + NaNO 3 (aq) ZnS(s) + 2HCl(aq)ZnCl 2 (aq) + H 2 S(g) 33

Example of a Double Replacement 34

Examples Identify each reaction as 1) combination, 2) decomposition, 3) single replacement, or 4) double replacement. A. 3Ba(s) + N 2 (g) Ba 3 N 2 (s) B. 2Ag(s) + H 2 S(aq)Ag 2 S(s) + H 2 (g) C. SiO 2 (s) + 4HF(aq) SiF 4 (s) + 2H 2 O(l) D. PbCl 2 (aq) + K 2 SO 4 (aq) 2KCl(aq) + PbSO 4 (s) E. K 2 CO 3 (s) K 2 O(aq) + CO 2 (g) 35

Chapter 5 Chemical Quantities and Reactions 5.6 Oxidation-Reduction Reactions 36

Oxidation and Reduction An oxidation-reduction reaction provides us with energy from food. provides electrical energy in batteries. occurs when iron rusts. 4Fe(s) + 3O 2 (g) 2Fe 2 O 3 (s) 37

Electron Loss and Gain An oxidation-reduction reaction involves a transfer of electrons from one reactant to another. oxidation as a loss of electrons (LEO). reduction as a gain of electrons (GER). 38

Oxidation and Reduction 39

Zn and Cu2+ Zn and Cu Zn(s) Zn 2+ (aq) + 2e- oxidation silver metal Cu 2+ (aq) + 2e- Cu(s) reduction blue solution orange Copyright © 2009 by Pearson Education, Inc.

Electron Transfer from Zn to Cu2+ Electron Transfer from Zn to Cu 2+ Oxidation: loss of electrons Reduction: gain of electrons 41 Copyright © 2009 by Pearson Education, Inc.

Examples Identify each of the following as 1) oxidation or 2) reduction. __A. Sn(s) Sn 4+ (aq) + 4e − __B. 2H + (aq) + 2e- H 2 (g) __C. Cl 2 (g) + 2e − 2Cl - (aq) 42

Writing Oxidation and Reduction Reactions Write the separate oxidation and reduction reactions for the following equation. 2Cs(s) + F 2 (g) 2CsF(s) A cesium atom loses an electron to form cesium ion. Cs(s) Cs + (s) + 1e − oxidation Fluorine atoms gain electrons to form fluoride ions. F 2 (s) + 2e - 2F − (s) reduction 43

Examples In light-sensitive sunglasses, UV light initiates an oxidation-reduction reaction. uv light Ag + + Cl − Ag + Cl A. Which reactant is oxidized? B. Which reactant is reduced? 44

Examples Identify the substances that are oxidized and reduced in each of the following reactions. A. Mg(s) + 2H + (aq) Mg 2+ (aq) + H 2 (g) B. 2PbO(s) 2Pb(s) + O 2 (g) 45