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Chapter Menu. Sec tio n 6.1 Chemical Equations Section 6.2 Types of Reactions Section 6.3 Nature of Reactions. Click a hyperlink to view the corresponding slides. Chapter Menu. Chemical Equations. Relate chemical changes and macroscopic properties.

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  1. Chapter Menu Section 6.1Chemical Equations Section 6.2 Types of Reactions Section 6.3 Nature of Reactions Click a hyperlink to view the corresponding slides. Chapter Menu

  2. Chemical Equations • Relate chemical changes and macroscopic properties. • Demonstrate how chemical equations describe chemical reactions. • Illustrate how to balance chemical reactions by changing coefficients. Section 6.1

  3. Chemical Equations energy: the capacity to do work Section 6.1

  4. Chemical Equations reactant product coefficient Balanced chemical equations represent chemical reactions. Section 6.1

  5. Chemical Reactions • When substances undergo chemical changes, observable differences usually occur. • color changes • precipitation of a solid • energy changes • odor changes • gas release Section 6.1

  6. Chemical Equations • Chemists use statements called equations to represent chemical reactions. • A substance that undergoes a reaction is called a reactant. • When reactants undergo a chemical change, each new substance formed is called a product. Section 6.1

  7. Chemical Equations (cont.) • To express chemical reactions, scientists use word equations, chemical equations, and symbols to indicate the physical state of the substances. • In word equations, acetic acid + sodium hydrogen carbonate → sodium acetate + water + carbon dioxide reads as “acetic acid and sodium hydrogen carbonate react to produce sodium acetate, water, and carbon dioxide”. Section 6.1

  8. Chemical Equations (cont.) • Chemical equations use symbols and formulas to represent the reactants and products. HC2H3O2 + NaHCO3 → NaC2H3O2 + H2O + CO2 Section 6.1

  9. Chemical Equations (cont.) • An endothermic reaction is a reaction in which energy is absorbed. • An exothermic reaction is a reaction in which energy is released. Section 6.1

  10. Balanced Chemical Equations • The most fundamental law in chemistry is the law of conservation of mass: Matter is neither created nor destroyed. Section 6.1

  11. Balanced Chemical Equations (cont.) • The law of conservation of atoms: The number and kinds of atoms present in the reactants of a chemical reaction are the same as those present in the product. Section 6.1

  12. Balanced Chemical Equations (cont.) • A coefficient is a number, which is always positive, that is placed in front of the parts of a chemical reaction to indicate how many units are involved. Section 6.1

  13. Section Assessment Which is an indicator that a chemical change is taking place? A.color change B.gas release C.precipitation of a solid D.all of the above Section 6.1

  14. Section Assessment What is the product of a chemical reaction between iron and oxygen? A.rust B.liquid mercury C.precipitation D.steel Section 6.1

  15. Everyday Chemistry (page 192) • Liquid bleaches containing sodium hypochlorite are often sold in opaque, plastic containers because sunlight causes the compound to decompose to produce oxygen gas and sodium chloride. Write the balanced chemical equation for this reaction. 2NaClO(aq)  2NaCl(aq) + O2 (g) 2. Why do you think bleaches containing sodium hypochlorite tend to damage finer fabrics more than bleaches containing hydrogen peroxide? One of the products of sodium hypochlorite bleaching is hydrochloric acid. Hydrogen peroxide bleaching however, produces water, which is not harmful to fabrics.

  16. Section 6.1 Assessment (page 199) 5. Why is it important to balance a chemical equation? The Law of Conservation of Mass must be obeyed in a chemical reaction. The number and kinds of atoms present in the products must be the same as those present in the reactants. 6. Write balanced chemical equations for the reactions: • sodium metal + chlorine gas  sodium chloride crystals 2Na(s) + Cl2(g)  2NaCl (s) (b) Propane gas + oxygen  carbon dioxide gas + water vapor + energy C3H8(g) + 5O2(g)  3CO2(g) + 4H2O(g) + energy

  17. Section 6.1 Assessment (page 199) 6.(c) zinc metal + hydrochloric acid  zinc chloride solution + hydrogen gas Zn(s) + 2HCl(aq)  ZnCl2 (aq) + H2(g) 7. How can you tell whether a chemical reaction has taken place? Macroscopic changes that indicate a reaction has occurred are -color changes, -odor changes, -energy absorption or release, -gas release, and -precipitation of solids.

  18. Section 6.1 Assessment (page 199) 8. Use the Law of Conservation of Mass to determine the following: (a) Grams of CO2 that form from 4.00 g of C and 10.67 g of O2. C + O2  CO2 (14.67g) (b) Grams of water formed if 7.75 g H2CO3 forms 5.50 g CO2. H2CO3  H2O + CO2 (2.25 g)

  19. Section 6.1 Assessment (page 199) 9. In the catalytic converter of a car, a reaction occurs when nitrogen monoxide gas (NO) reacts with hydrogen gas. Ammonia gas and water vapor are formed. Write a balanced equation for this reaction. 2NO(g) + 5H2(g)  2NH3(g) + 2H2O(g)

  20. End of Section 6.1

  21. Types of Reactions • Distinguish among the five major types of chemical reactions. • Classify a reaction as belonging to one of five major types. Section 6.2

  22. Types of Reactions reactant: a substance that undergoes a reaction Section 6.2

  23. Types of Reactions synthesis decomposition single displacement double displacement combustion There are five types of chemical reactions: synthesis, decomposition, single-displacement, double-displacement, and combustion reactions. Section 6.2

  24. Why Reactions Are Classified • Classifying reactions can help in understanding the reaction and making predictions about it. Section 6.2

  25. Major Classes of Reactions • Whenever two or more substances combine to form a single product, the reaction is called a synthesis reaction. • A decomposition reaction is one in which a compound breaks down into two or more simpler substances. Section 6.2

  26. Major Classes of Reactions (cont.) • A single-displacement reaction is one in which one element takes the place of another in a compound. • A double-displacement reaction is one in which the positive ions of two ionic compounds are interchanged. • A combustion reaction is one in which a substance rapidly combines with oxygen to form one or more oxides. Section 6.2

  27. Major Classes of Reactions (cont.) Section 6.2

  28. Section Assessment A reaction in which one element takes the place of another is what type of reaction? A.combustion reaction B.synthesis reaction C.single displacement reaction D.double displacement reaction Section 6.2

  29. Section Assessment Which reaction forms oxides? A.single displacement reaction B.decomposition reaction C.synthesis reaction D.combustion reaction Section 6.2

  30. End of Section 6.2

  31. Nature of Reactions • Demonstrate factors that influence the direction of a reaction. • Classify factors that influence the rate of a reaction. Section 6.3

  32. Nature of Reactions synthesis: reaction in which two or more substances combine to form a single product. Section 6.3

  33. Nature of Reactions equilibrium dynamic equilibrium Le Châtelier’s principle soluble insoluble activation energy concentration limiting reactant catalyst enzyme inhibitor External factors modify the direction and rate of chemical reactions. Section 6.3

  34. Reversible Reactions • When no net change occurs in the amount of reactants and products, a system is said to be in equilibrium. • A dynamic equilibrium is a system in which opposite actions are taking place at the same rate. Section 6.3

  35. Reversible Reactions (cont.) • The reversible reaction will favor the direction that produces the most stable products, which are those that are least likely to change. • Le Châtelier’s principle states that if a stress is applied to a system at equilibrium, the system shifts in the direction that relieves the stress. Section 6.3

  36. Reversible Reactions (cont.) • A product that does not dissolve in water can be removed if all other products and the reactants dissolve in water. • A compound is soluble in a liquid if it dissolves in it. • A compound is insoluble if it does not dissolve in a liquid. Section 6.3

  37. Reversible Reactions (cont.) • Adding or removing energy, usually in the form of heat, can also influence the direction of a reaction. Section 6.3

  38. Activation Energy • For a reaction to occur between two substances, particles of those substances must collide with each other with enough force to cause a change to take place. • The amount of energy the particles must have when they collide is called the activation energyof the reaction. Section 6.3

  39. Speed Rate • To determine how fast a reaction is taking place, you can measure how quickly one of the reactants disappears or how quickly one of the products appears. • Most reactions go faster at higher temperatures. Section 6.3

  40. Speed Rate (cont.) • Raising the concentration, or amount of the substance present in a certain volume, will speed up a reaction because there are more particles per volume. Section 6.3

  41. Speed Rate (cont.) • When the limiting reactant, or the reactant in limited supply, is used up, the reaction stops and no new product is formed. Section 6.3

  42. Speed Rate (cont.) • A catalyst is a substance that speeds up the rate of a reaction without being permanently changed or used up itself. • Biological catalysts are called enzymes. • A substance that slows a reaction is called an inhibitor. Section 6.3

  43. Section Assessment What is a substance that slows a reaction called? A.inhibitor B.enzyme C.limiting reactant D.insoluble Section 6.3

  44. Section Assessment Which of the following does not affect the speed rate of a reaction? A.raising the temperature B.raising the concentration C.removing a catalyst D.none of the above Section 6.3

  45. Section Assessment Lowering concentration ___ the rate of reaction. A.decreases B.increases C.equalizes D.does not affect Section 6.3

  46. End of Section 6-3

  47. Key Concepts • Chemical equations—used to represent reactions—are written using symbols and formulas for elements and compounds. • Chemical equations can tell you how elements and compounds change during a reaction and whether a reaction is endothermic or exothermic. • Equations are balanced by changing coefficients. • A balanced chemical equation reflects the law of conservation of mass. Study Guide 1

  48. Key Concepts • Although thousands of individual chemical reactions are known, most can be classified into five major classes that are based on patterns of behavior of reactants and products. • The five general classes of reactions are synthesis, decomposition, single-displacement, double-displacement, and combustion. • Sometimes classes of reactions overlap. For example, some combustion reactions are also synthesis reactions. Study Guide 2

  49. Key Concepts • Reversible reactions are those in which the products can react to reform the reactants. • Equilibrium occurs when forward and reverse reactions take place at the same rate. • At equilibrium, there is no net change in the amounts of products and reactants. • According to Le Châtelier’s principle, if a stress is applied to a system at equilibrium, the system shifts in the direction that relieves the stress. Study Guide 3

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