1. 7.2 Types of Reactions The walls of this cave are limestone. When hydrochloric acid is dropped on limestone, a chemical reaction occurs that produces a gas. Geologists use this reaction to determine whether a rock sample contains the mineral calcium carbonate, CaCO 3.

2. 7.2 Types of Reactions What are the general types of chemical reactions? Classifying Reactions Some general types of chemical reactions are synthesis reactions, decomposition reactions, single-replacement reactions, double-replacement reactions, and combustion reactions.

3. 7.2 Types of Reactions Just as you can classify matter into different types, you can classify chemical reactions into different types. Reactions are often classified by the type of reactant or the number of reactants and products. Classifying Reactions

4. 7.2 Types of Reactions Synthesis A synthesis reaction is a reaction in which two or more substances react to form a single substance. The reactants may be either elements or compounds. The product synthesized is always a compound. The general equation for a synthesis reaction is A + B  AB Classifying Reactions

5. 7.2 Types of Reactions Decomposition A decomposition reaction is a reaction in which a compound breaks down into two or more simpler substances. The reactant in a decomposition reaction must be a compound. The products may be elements or compounds. The general equation for a decomposition reaction is AB  A + B Classifying Reactions

6. 7.2 Types of Reactions Single Replacement A single-replacement reaction is a reaction in which one element takes the place of another element in a compound. Single- replacement reactions have the general form A + BC  B + AC Classifying Reactions

7. 7.2 Types of Reactions As copper replaces silver in the silver nitrate solution in a single-replacement reaction, the solution turns blue, and silver crystals form on the wire. Cu + 2AgNO 3  2Ag + Cu(NO 3 ) 2 Classifying Reactions

8. 7.2 Types of Reactions Double Replacement A double-replacement reaction is one in which two different compounds exchange positive ions and form two new compounds. The general form of a double replacement reaction is AB + CD  AD + CB Two replacements take place in this reaction. A replaces C, and C replaces A. Classifying Reactions

9. 7.2 Types of Reactions When potassium iodide solution is poured into a solution of lead(II) nitrate, a double-replacement reaction takes place. Lead(II) iodide forms as a yellow precipitate. Potassium nitrate remains in solution. Pb(NO 3 ) 2 + 2KI  PbI 2 + 2KNO 3 Classifying Reactions

10. 7.2 Types of Reactions When geologists test the calcium carbonate content in a rock, they use a double- replacement reaction. CaCO 3 + 2HCl  CaCl 2 + H 2 CO 3 The product carbonic acid,H 2 CO 3, then decomposes into carbon dioxide gas and water. H 2 CO 3  CO 2 + H 2 O Classifying Reactions

11. 7.2 Types of Reactions Combustion A combustion reaction is one in which a substance reacts rapidly with oxygen, often producing heat and light. The main component of natural gas is methane. When methane burns in oxygen, a combustion reaction occurs. CH 4 + 2O 2  CO 2 + 2H 2 O Classifying Reactions

12. 7.2 Types of Reactions A Bunsen burner generates heat and light by the combustion of natural gas. Classifying Reactions

13. 7.2 Types of Reactions How did the discovery of subatomic particles affect the classification of reactions? Reactions as Electron Transfers The discovery of subatomic particles enabled scientists to classify certain chemical reactions as transfers of electrons between atoms.

14. 7.2 Types of Reactions A reaction in which electrons are transferred from one reactant to another is called an oxidation-reduction reaction, or redox reaction. Reactions as Electron Transfers

15. 7.2 Types of Reactions Oxidation For a long time, people have known that metals react with oxygen. Calcium reacts with oxygen and forms calcium oxide (CaO). Iron reacts with oxygen and forms rust, or iron(III) oxide (Fe 2 O 3 ). These types of synthesis reactions, in which a metal combines with oxygen, have been classified as oxidations. Reactions as Electron Transfers

16. 7.2 Types of Reactions Reduction The process in which an element gains electrons during a chemical reaction is called reduction. As calcium atoms lose electrons during the synthesis of calcium oxide, the oxygen atoms gain electrons. As each neutral oxygen atom gains two electrons, it becomes an ion with a charge of 2 –. O + 2e –  O 2– Reactions as Electron Transfers

17. 7.2 Types of Reactions Oxidation and reduction always occur together. When one element loses electrons, another element must gain electrons. A reactant is said to be reduced if it gains electrons. A reactant is oxidized if it loses electrons. Oxidation-reduction reactions do not always involve complete transfers of electrons. For example, in the synthesis of water, hydrogen is oxidized, and oxygen is reduced, but the transfer of electrons is only partial. Reactions as Electron Transfers

18. 7.2 Types of Reactions Assessment Questions 1.Which of these statements best describes a double- replacement reaction? a.Two different compounds exchange positive ions and form two new compounds. b.An element takes the place of another element in a compound. c.One compound breaks down into two or more simpler substances. d.Two or more substances react to form a single substance.

19. 7.2 Types of Reactions Assessment Questions 1.Which of these statements best describes a double- replacement reaction? a.Two different compounds exchange positive ions and form two new compounds. b.An element takes the place of another element in a compound. c.One compound breaks down into two or more simpler substances. d.Two or more substances react to form a single substance. ANS:A

20. 7.2 Types of Reactions Assessment Questions 2.Which of the following statements about oxidation- reduction reactions is true? a.Oxidation-reduction reactions always involve a transfer of protons between atoms. b.Oxidation is the process in which electrons are gained. c.Oxidation and reduction always occur together. d.Oxidation-reduction reactions always involve oxygen as one of the reactants.

21. 7.2 Types of Reactions Assessment Questions 2.Which of the following statements about oxidation- reduction reactions is true? a.Oxidation-reduction reactions always involve a transfer of protons between atoms. b.Oxidation is the process in which electrons are gained. c.Oxidation and reduction always occur together. d.Oxidation-reduction reactions always involve oxygen as one of the reactants. ANS:C