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  1. Chemical Reactions Section 9.1Reactions and Equations Section 9.2Classifying Chemical Reactions Section 9.3Reactions in Aqueous Solutions Click a hyperlink or folder tab to view the corresponding slides. Exit Chapter Menu

  2. Section 9.1 Reactions and Equations Recognizeevidence of chemical change. chemical change:a process involving one or more substances changing into a new substance Representchemical reactions with equations. Balancechemical equations. chemical reaction reactant product chemical equation coefficient Chemical reactions are represented by balanced chemical equations. Section 9-1

  3. Chemical Reactions The process by which one or more substances are rearranged to form different substances is called a chemical reaction. Section 9-1

  4. Chemical Reactions (cont.) Evidence of a chemical reaction • Change in temperature • Change in color • Odor, gas, or bubbles may form. Section 9-1

  5. Representing Chemical Reactions Chemists use statements called equations to represent chemical reactions. Reactantsare the starting substances. Productsare the substances formed in the reaction. This table summarizes the symbols used in chemical equations. Section 9-1

  6. Representing Chemical Reactions (cont.) In word equations, aluminum(s) + bromine(l) → aluminum bromide(s) reads as “aluminum and bromine react to produce aluminum bromide”. Skeleton equations use symbols and formulas to represent the reactants and products. Al(s) + Br(l) → AlBr3(s) Skeleton equations lack information about how many atoms are involved in the reaction. Section 9-1

  7. Representing Chemical Reactions (cont.) A chemical equationis a statement that uses chemical formulas to show the identities and relative amounts of the substances involved in a chemical reaction. Section 9-1

  8. Balancing Chemical Equations This figure shows the balanced equation for the reaction between aluminum and bromine. Section 9-1

  9. Balancing Chemical Equations (cont.) A coefficientin a chemical equation is the number written in front of a reactant or product, describing the lowest whole-number ratio of the amounts of all the reactants and products. Section 9-1

  10. Balancing Chemical Equations (cont.) Section 9-1

  11. Balancing Chemical Equations (cont.) Section 9-1

  12. Balancing Chemical Equations (cont.) Section 9-1

  13. Balancing Chemical Equations (cont.) The most fundamental law in chemistry is the law of conservation of mass. Balanced equations show this law. Section 9-1

  14. Balancing Chemical Equations (cont.) Section 9-1

  15. A B C D Section 9.1 Assessment Which of the following is NOT a chemical reaction? A.a piece of wood burning B.a car rusting ice cube melting into water litmus paper turning blue Section 9-1

  16. A B C D Section 9.1 Assessment What is the coefficient of bromine in the equation 2Al(s) + 3Br2(l) → 2AlBr3(s)? A.1 B.2 C.3 D.6 Section 9-1

  17. End of Section 9-1

  18. Section 9.2 Classifying Chemical Reactions Classify chemical reactions. metal: an element that is a solid at room temperature, a good conductor of heat and electricity, and is generally shiny Identify the characteristics of different classes of chemical reactions. Section 9-2

  19. Section 9.2 Classifying Chemical Reactions (cont.) synthesis reaction combustion reaction decomposition reaction single-replacement reaction double-replacement reaction precipitate There are four types of chemical reactions: synthesis, combustion, decomposition, and replacement reactions. Section 9-2

  20. Types of Chemical Reactions Chemists classify reactions in order to organize the many types. A synthesis reaction is a reaction in which two or more substances react to produce a single product. Section 9-2

  21. Types of Chemical Reactions (cont.) When two elements react, the reaction is always a synthesis reaction. Section 9-2

  22. Types of Chemical Reactions (cont.) In a combustion reaction, oxygen combines with a substance and releases energy in the form of heat and light. Heated hydrogen reacts with oxygen to produce heat and water in a combustion reaction. This is also a synthesis reaction. Section 9-2

  23. Decomposition Reactions A decomposition reactionis one in which a single compound breaks down into two or more elements or new compounds. Decomposition reactions often require an energy source, such as heat, light, or electricity, to occur. Section 9-2

  24. Replacement Reactions • A reaction in which the atoms of one element replace the atoms of another element in a compound is called a single replacement reaction. A + BX → AX + B Section 9-2

  25. Replacement Reactions (cont.) A metal will not always replace a metal in a compound dissolved in water because of differing reactivities. An activity series can be used to predict if reactions will occur. Section 9-2

  26. Replacement Reactions (cont.) Halogens frequently replace other halogens in replacement reactions. Halogens also have different reactivities and do not always replace each other. Section 9-2

  27. Replacement Reactions (cont.) Double replacement reactionsoccur when ions exchange between two compounds. This figure shows a generic double replacement equation. Section 9-2

  28. Replacement Reactions (cont.) The solid product produced during a chemical reaction in a solution is called a precipitate. All double replacement reactions produce either water, a precipitate, or a gas. Section 9-2

  29. Replacement Reactions (cont.) This table shows the steps to write double replacement reactions. Section 9-2

  30. Replacement Reactions (cont.) This table summarizes different ways to predict the products of a chemical reaction. Section 9-2

  31. A B C D Section 9.2 Assessment Which of the following is NOT one of the four types of reactions? A.deconstructive B.synthesis C.single replacement D.double replacement Section 9-2

  32. A B C D Section 9.2 Assessment The following equation is what type of reaction? KCN(aq) + HBr(aq) → KBr(aq) + HCN(g) A.deconstructive B.synthesis C.single replacement D.double replacement Section 9-2

  33. End of Section 9-2

  34. Section 9.3 Reactions in Aqueous Solutions Describe aqueous solutions. Write complete ionic and net ionic equations for chemical reactions in aqueous solutions. Predict whether reactions in aqueous solutions will produce a precipitate, water, or a gas. solution: a uniform mixture that might contain solids, liquids, or gases Section 9-3

  35. Section 9.3 Reactions in Aqueous Solutions (cont.) aqueous solution solute solvent complete ionic equation spectator ion net ionic equation Double-replacement reactions occur between substances in aqueous solutions and produce precipitates, water, or gases. Section 9-3

  36. Aqueous Solutions An aqueous solutioncontains one or more dissolved substances (called solutes) in water. The solvent is the most plentiful substance in a solution. Section 9-3

  37. Aqueous Solutions (cont.) Water is always the solvent in an aqueous solution. There are many possible solutes—sugar and alcohol are molecular compounds that exist as molecules in aqueous solutions. Compounds that produce hydrogen ions in aqueous solutions are acids. Section 9-3

  38. Aqueous Solutions (cont.) Ionic compounds can also be solutes in aqueous solutions. When ionic compounds dissolve in water, their ions separate in a process called dissociation. Section 9-3

  39. Types of Reactions in Aqueous Solutions When two solutions that contain ions as solutes are combined, the ions might react. If they react, it is always a double replacement reaction. Three products can form: precipitates, water, or gases. Section 9-3

  40. Types of Reactions in Aqueous Solutions (cont.) • Aqueous solutions of sodium hydroxide and copper(II) chloride react to form the precipitate copper(II) hydroxide. 2NaOH(aq) + CuCl2(aq) → 2NaCl(aq) + Cu(OH)2(s) • Ionic equations that show all of the particles in a solution as they actually exist are called complete ionic equations. 2Na+(aq) + 2OH–(aq) + Cu2+ (aq)+ 2Cl–(aq) → 2Na+(aq) + 2Cl–(aq) + Cu(OH)2(s) Section 9-3

  41. Types of Reactions in Aqueous Solutions (cont.) Ions that do not participate in a reaction are called spectator ionsand are not usually written in ionic equations. • Formulas that include only the particles that participate in reactions are called net ionic equations. 2OH–(aq) + Cu2+(aq) → Cu(OH)2(s) Section 9-3

  42. Types of Reactions in Aqueous Solutions (cont.) Some reactions produce more water molecules. • No evidence of a chemical reaction is observable. HBr(aq) + NaOH(aq) → H2O(l) + NaBr(aq) • Without spectator ions H+(aq) + OH–(aq) → H2O(l). Section 9-3

  43. Types of Reactions in Aqueous Solutions (cont.) • Gases that are commonly produced are carbon dioxide, hydrogen cyanide, and hydrogen sulfide. 2HI(aq) + Li2S(aq) → H2S(g) + 2LiI(aq) Section 9-3

  44. Types of Reactions in Aqueous Solutions (cont.) Another example is mixing vinegar and baking soda, which produces carbon dioxide gas. HCl(aq) + NaHCO3(aq) → H2CO3(aq) + NaCl(aq) • H2CO3(aq) decomposes immediately. H2CO3(aq) → H2O(l) + CO2(g) Section 9-3

  45. Types of Reactions in Aqueous Solutions (cont.) Two reactions can be combined and represented by a single chemical reaction. Section 9-3

  46. Types of Reactions in Aqueous Solutions (cont.) Reaction 1 HCl(aq) + NaHCO3(aq) → H2CO3(aq) + NaCl(aq) Reaction 2 H2CO3(aq) → H2O(l) + CO2(g) Combined equation HCl(aq) + NaHCO3(aq) + H2CO3(aq) → H2CO3(aq) + NaCl(aq) + H2O(l) + CO2(g) Overall equation HCl(aq) + NaHCO3(aq) → H2O(l) + CO2(g) + NaCl(aq) Section 9-3

  47. A B C D Section 9.3 Assessment What is the solvent in an aqueous solution? A.hydrogen B.sodium ions C.water D.alcohol Section 9-3

  48. A B C D Section 9.3 Assessment An equation that includes only the particles that participate in a reaction is called: ionic equation B.spectator ions C.complete ionic equation D.reduced ionic equation Section 9-3

  49. End of Section 9-3