1. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu A chemical reaction is the process by which one or more substances change into one or more new substances. Reactants are the original substances in a chemical reaction. Products are the substances that are created in a chemical reaction. Section 1 Describing Chemical Reactions Chapter 8 Chemical Reaction

2. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Evidence of a Chemical Reaction Section 1 Describing Chemical Reactions Chapter 8

3. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Evidence of a Chemical Reaction Section 1 Describing Chemical Reactions solution color changes solution bubbles copper is used up Chapter 8

4. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chemical Reaction Versus Physical Change chemical change – new substance forms with properties that differ from original substance density boiling point melting point physical change - changes of state evaporation condensation melting freezing Section 1 Describing Chemical Reactions Chapter 8

5. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Reactions and Energy Changes Energy can be released in a chemical reaction (exothermic). methane + oxygen  carbon dioxide + water + energy Energy is a product. Energy can be absorbed in a chemical reaction (endothermic). dinitrogen tetroxide + energy  nitrogen dioxide Energy is a reactant. Section 1 Describing Chemical Reactions Chapter 8

6. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Constructing a Chemical Equation A chemical equation shows the chemical formulas and relative amounts of all reactants and products. A word equation contains the names of the reactants and products. Equations must be balanced. Section 1 Describing Chemical Reactions Chapter 8

7. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Writing a Word Equation or Formula Equation methane + oxygen  carbon dioxide + water ?CH 4 + ?O 2  ?CO 2 + ?H 2 O Section 1 Describing Chemical Reactions Chapter 8

8. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Equations and Reaction Information Section 1 Describing Chemical Reactions Chapter 8

9. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 8 Section 2 Continued 12/09/15 Section 2 Balancing Chemical Equations Chapter 8

10. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Reactions Conserve Mass Mass cannot be created or destroyed by a chemical or physical change Equations must be balanced. ?Na + ?H 2 O  ?NaOH + ?H 2 Section 2 Balancing Chemical Equations Chapter 8

11. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Balancing Equations The number of atoms for each element must be the same on the reactants’ side and on the products’ side. A coefficient multiplies the number of atoms of each element in the formula that follows. H 2 O: 2 hydrogen atoms, 1 oxygen atom 2H 2 O: 4 hydrogen atoms, 2 oxygen atoms Section 2 Balancing Chemical Equations Chapter 8

12. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Balancing Equations Sample Problem A Balance the equation for the reaction of iron(III) oxide with hydrogen to form iron and water. Section 2 Balancing Chemical Equations Chapter 8

13. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Balancing Equations Sample Problem A Solution 1.Identify reactants and products. reactants products Fe 2 O 3 + H 2  Fe + H 2 O 2.Count atoms Section 2 Balancing Chemical Equations ReactantsProductsBalanced? Unbalanced formula equationFe 2 O 3 + H 2 Fe + H 2 O Iron atoms21no Oxygen atoms31no Hydrogen atoms22yes 332 Chapter 8 3.Insert coefficients.

14. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Reactions Conserve Mass Balanced equations show mass conservation ?Na + ?H 2 O  ?NaOH + ?H 2 2Na + 2H 2 O  2NaOH + H 2 Never change subscripts to balance equations Unbalanced: H 2 + O 2  H 2 O Incorrect:H 2 + O 2  H 2 O 2 H 2 O  H 2 O 2 Correct:2H 2 + O 2  2H 2 O Section 2 Balancing Chemical Equations Chapter 8

15. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Reactions Conserve Mass Section 2 Balancing Chemical Equations Chapter 8

16. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Balancing Equations Sample Problem C Aluminum reacts with arsenic acid, HAsO 3, to form H 2 and aluminum arsenate. Write a balanced equation for this reaction. Section 2 Balancing Chemical Equations Chapter 8

17. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Balancing Equations Sample Problem C Solution 1. Identify reactants and products. reactants products Al + HAsO 3  H 2 + Al(AsO 3 ) 3 2. Count Atoms Section 2 Balancing Chemical Equations ReactantsProductsBalanced? Unbalanced formula equationAl + HAsO 3 H 2 + Al(AsO 3 ) 3 Iron atoms 11yes Oxygen atoms 12no Hydrogen atoms 13no 3226 Chapter 8 3. Insert coefficients

18. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 3 Classifying Chemical Reactions Chapter 8 Section 3 12/09/15 Chapter 8

19. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 3 Classifying Chemical Reactions Combustion Reactions A combustion reaction is a reaction of a carbon- based compound with oxygen. Combustion of propane: C 3 H 8 + 5O 2  3CO 2 + 4H 2 O Combustion of ethanol: CH 3 CH 2 OH + 3O 2  2CO 2 + 3H 2 O Chapter 8

20. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 3 Classifying Chemical Reactions Synthesis Reactions In a synthesis reaction a single compound forms from two or more reactants. Two elements form a binary compound C + O 2  CO 2 2C + O 2  2CO Two compounds form a ternary compound CaO(s) + H 2 O(l)  Ca(OH) 2 (s) CO 2 (g) + H 2 O(l)  H 2 CO 3 (aq) Chapter 8

21. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 3 Classifying Chemical Reactions Decomposition Reactions In a decomposition reaction a single compound breaks down, often with the input of energy, into two or more elements or simpler compounds. Decomposition of water electricity heat Chapter 8 CaCO 3 (s)CaO(s) + CO 2 (g) A metal carbonate decomposes to form a metal oxide and carbon dioxide. 2H 2 O(l)O 2 (g) + 2H 2 (g)

22. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 3 Classifying Chemical Reactions Displacement Reactions In a single-displacement reaction a single element reacts with a compound and displaces another element from the compound. 2Al(s) + 3CuCl 2 (aq)  2AlCl 3 (aq) + 3Cu(s) Aluminum displaces copper. Chapter 8

23. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 3 Classifying Chemical Reactions Double-Displacement Reactions In a double-displacement reaction two compounds in aqueous solution appear to exchange ions and form two new compounds. One of the products must be a solid precipitate, a gas, or a molecular compound, such as water. HCl(aq) + NaOH(aq)  HOH(l) + NaCl(aq) Chapter 8