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Major Classes of Reactions If you can classify a reaction into one of five major categories by recognizing patterns that occur, you already know a lot.

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Presentation on theme: "Major Classes of Reactions If you can classify a reaction into one of five major categories by recognizing patterns that occur, you already know a lot."— Presentation transcript:

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2 Major Classes of Reactions If you can classify a reaction into one of five major categories by recognizing patterns that occur, you already know a lot about the reaction. Chemical Reactions and Equations: Basic Concepts Topic 8 Topic 8

3 Major Classes of Reactions In one type of reaction, two substances either elements or compoundscombine to form a compound. Whenever two or more substances combine to form a single product, the reaction is called a synthesis reaction. Chemical Reactions and Equations: Basic Concepts Topic 8 Topic 8

4 A Synthesis Reaction When iron rusts, iron metal and oxygen gas combine to form one new substance, iron(III) oxide. The balanced equation for this synthesis reaction shows that there is more than one reactant but only one product. Chemical Reactions and Equations: Basic Concepts Topic 8 Topic 8

5 A Synthesis Reaction Chemical Reactions and Equations: Basic Concepts Topic 8 Topic 8

6 Major Classes of Reactions In a decomposition reaction, a compound breaks down into two or more simpler substances. The compound may break down into individual elements, such as when mercury(II) oxide decomposes into mercury and oxygen. Chemical Reactions and Equations: Basic Concepts Topic 8 Topic 8

7 Major Classes of Reactions The products may be an element and a compound, such as when hydrogen peroxide decomposes into water and oxygen. The compound may break down into simpler compounds. Chemical Reactions and Equations: Basic Concepts Topic 8 Topic 8

8 A Decomposition Reaction When ammonium nitrate is heated to a high temperature, it explosively breaks down into dinitrogen monoxide and water. The decomposition reaction taking place is represented by a balanced equation that shows one reactant and more than one product. Chemical Reactions and Equations: Basic Concepts Topic 8 Topic 8

9 A Decomposition Reaction Chemical Reactions and Equations: Basic Concepts Topic 8 Topic 8

10 Major Classes of Reactions In a single-displacement reaction, one element takes the place of another in a compound. The element can replace the first part of a compound, or it can replace the last part of a compound. Chemical Reactions and Equations: Basic Concepts Topic 8 Topic 8

11 Single Displacement If an iron nail is placed into an aqueous solution of copper(II) sulfate, the iron displaces the copper ions in solution, and copper metal forms on the nail. Chemical Reactions and Equations: Basic Concepts Topic 8 Topic 8

12 Single Displacement Chemical Reactions and Equations: Basic Concepts Topic 8 Topic 8

13 Major Classes of Reactions In double-displacement reactions, the positive portions of two ionic compounds are interchanged. For a double-displacement reaction to take place, at least one of the products must be a precipitate, gas or water. Chemical Reactions and Equations: Basic Concepts Topic 8 Topic 8

14 Double Displacement When clear aqueous solutions of lead(II) nitrate and potassium iodine are mixed, a double-displacement reaction takes place and a yellow solid appears in the mixture. This solid is lead(II) iodine, and it precipitates out because it is insoluble in water, unlike the two reactants and the other product. Chemical Reactions and Equations: Basic Concepts Topic 8 Topic 8

15 Double Displacement Chemical Reactions and Equations: Basic Concepts Topic 8 Topic 8

16 Reactions in Aqueous Solutions Another example of a double-replacement reaction that produces a precipitate occurs when aqueous solutions of sodium chloride and silver nitrate are mixed to form a precipitate of solid silver chloride. Chemical Reactions and Equations: Additional Concepts Topic 8 Topic 8

17 Reactions that form water or a gas Some double-replacement reactions in aqueous solution produce water or a gas (or both) rather than a precipitate. In such cases, the water or gas is shown as a product in the net chemical equation, as are the ions that produced it. The following example problem illustrates this concept. Chemical Reactions and Equations: Additional Concepts Topic 8 Topic 8

18 Reactions that form water or a gas When hydrochloric acid and potassium hydroxide solutions are mixed, water results, together with an aqueous solution of potassium chloride. Write the balanced chemical equation, for this reaction. Chemical Reactions and Equations: Additional Concepts Topic 8 Topic 8

19 Reactions that form water or a gas The balanced chemical equation is the same as the skeleton equation. Chemical Reactions and Equations: Additional Concepts Topic 8 Topic 8

20 Major Classes of Reactions A combustion reaction is one in which a substance rapidly combines with oxygen to form one or more oxides. Chemical Reactions and Equations: Basic Concepts Topic 8 Topic 8

21 Combustion When welding is done with an acetylene torch, acetylene combines with oxygen to form carbon dioxide and water. This combustion reaction is exothermic, and enough energy is released to melt metal. Chemical Reactions and Equations: Basic Concepts Topic 8 Topic 8

22 Combustion Chemical Reactions and Equations: Basic Concepts Topic 8 Topic 8

23 Basic Assessment Questions Question 3 Identify each of the following skeleton equations as representing a synthesis reaction, a combustion reaction, both synthesis and combustion, or decomposition reaction. Balance each equation if necessary. Topic 8 Topic 8

24 Basic Assessment Questions synthesis; Answer 3a Question 3a Topic 8 Topic 8

25 Basic Assessment Questions decomposition; already balanced Answer 3b Question 3b Topic 8 Topic 8


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