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Understanding Chemical Equations & Reactions

Explore the process of chemical reactions, balancing equations, and identifying evidence and signs of reactions. Understand the transformation of substances and the conservation of mass through visual and practical examples.

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Understanding Chemical Equations & Reactions

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  1. Chemical Equations and Reactions Chapter 8 Table of Contents Section 1Describing Chemical Reactions Section 2Balancing Chemical Equations Section 3Classifying Chemical Reactions Section 4Writing Net Ionic Equations

  2. Section1 Describing Chemical Reactions Chapter 8 Bellringer • For the following situations, list observations that you think indicate that a chemical reaction has taken place: • a cut apple turns brown • an egg changes when it cooks • a log burns • a car rusts

  3. Section1 Describing Chemical Reactions Chapter 8 Objectives (Slides 2-15) • List evidence that suggests that a chemical reaction has occurred and evidence that proves that a chemical reaction has occurred. • Describe a chemical reaction by using a word equation and a formula equation. • Interpret notations in formula equations, such as those relating to states of matter or reaction conditions.

  4. Section1 Describing Chemical Reactions Chapter 8 Chemical Reaction • 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.

  5. Section1 Describing Chemical Reactions Chapter 8 Evidence of a Chemical Reaction

  6. Visual Concepts Chapter 8 Signs of a Chemical Reaction

  7. Visual Concepts Chapter 8 Precipitate

  8. Section1 Describing Chemical Reactions Chapter 8 Evidence of a Chemical Reaction • solution color changes • solution bubbles • copper is used up

  9. Section1 Describing Chemical Reactions Chapter 8 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

  10. Section1 Describing Chemical Reactions Chapter 8 Reactions and Energy Changes • Energy can be released in a chemical reaction. • methane + oxygen  carbon dioxide + water + energy • Energy is a product. • Energy can be absorbed in a chemical reaction. • dinitrogen tetroxide +energy nitrogen dioxide • Energy is a reactant.

  11. Section1 Describing Chemical Reactions Chapter 8 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.

  12. Section1 Describing Chemical Reactions Chapter 8 Writing a Word Equation or Formula Equation methane + oxygen  carbon dioxide + water ?CH4 + ?O2  ?CO2 + ?H2O

  13. Section1 Describing Chemical Reactions Chapter 8 Equations and Reaction Information • Physical States • NaHCO3(s) + HC2H3O2(aq)  NaC2H3O2(aq) + CO2(aq) + H2O(l) • solid liquid aqueous solutions • Reaction Conditions • 350°C, 25 000 kPa N2(g) + 3H2(g) 2NH3(g) catalyst

  14. Section1 Describing Chemical Reactions Chapter 8 Equations and Reaction Information

  15. Visual Concepts Chapter 8 Chemical Equation

  16. Section2 Balancing Chemical Equations Chapter 8 Bellringer • Write a word equation for baking a cake. • Does the cake have the same properties as the ingredients? • Answer: • sugar + flour + eggs + vanilla + salt  cake • The properties are different.

  17. Section2 Balancing Chemical Equations Chapter 8 Objectives (slides 16- 27) • Relate the conservation of mass to the rearrangement of atoms in a chemical reaction. • Write and interpret a balanced chemical equation for a reaction, and relate conservation of mass to the balanced equation.

  18. Section2 Balancing Chemical Equations Chapter 8 Reactions Conserve Mass • Mass cannot be created or destroyed by a chemical or physical change • Equations must be balanced. • ?Na + ?H2O  ?NaOH + ?H2

  19. Section2 Balancing Chemical Equations Chapter 8 Balancing Equations • The number of atoms for each element must be the same on the reactants’ side and on the products’ side. • Acoefficient multiplies the number of atoms of each element in the formula that follows. • H2O: 2 hydrogen atoms, 1 oxygen atom • 2H2O: 4 hydrogen atoms, 2 oxygen atoms

  20. Visual Concepts Chapter 8 Reading a Chemical Equation

  21. Section2 Balancing Chemical Equations Chapter 8 Balancing Equations Sample Problem A Balance the equation for the reaction of iron(III) oxide with hydrogen to form iron and water.

  22. Section2 Balancing Chemical Equations Chapter 8 Balancing Equations • Sample Problem A Solution • Identify reactants and products. • reactants products • Fe2O3 + H2  Fe + H2O • Count atoms 3 2 3 • Insert coefficients.

  23. Section2 Balancing Chemical Equations Chapter 8 Reactions Conserve Mass • Balanced equations show mass conservation • ?Na + ?H2O  ?NaOH + ?H2 • 2Na + 2H2O  2NaOH + H2 • Never change subscripts to balance equations • Unbalanced: H2 + O2  H2O • Incorrect: H2 + O2  H2O2 • H2O  H2O2 • Correct: 2H2 + O2  2H2O

  24. Section2 Balancing Chemical Equations Chapter 8 Reactions Conserve Mass

  25. Section2 Balancing Chemical Equations Chapter 8 Polyatomic Ions can be balanced as a group

  26. Section2 Balancing Chemical Equations Chapter 8 Balancing Equations Sample Problem C Aluminum reacts with arsenic acid, HAsO3, to form H2 and aluminum arsenate. Write a balanced equation for this reaction.

  27. Section2 Balancing Chemical Equations Chapter 8 Balancing Equations Sample Problem C Solution 1. Identify reactants and products. reactants products Al + HAsO3  H2 + Al(AsO3)3 2. Count Atoms 2 6 3 2 3. Insert coefficients

  28. Section3 Classifying Chemical Reactions Chapter 8 Bellringer • Describe the following terms. • synthesis • decomposition • displacement

  29. Section3 Classifying Chemical Reactions Chapter 8 Objectives (slides 28-49) • Identify combustion reactions, and write chemical equations that predict the products. • Identify synthesis reactions, and write chemical equations that predict the products. • Identify decomposition reactions, and write chemical equations that predict the products.

  30. Section3 Classifying Chemical Reactions Chapter 8 Objectives, continued • Identify displacement reactions, and use the activity series to write chemical equations that predict the products. • Identify double-displacement reactions, and write chemical equations that predict the products.

  31. Section3 Classifying Chemical Reactions Chapter 8 Combustion Reactions • A combustion reaction is a reaction of a carbon-based compound with oxygen. • Combustion of propane: • C3H8 + 5O2 3CO2 + 4H2O • Combustion of ethanol: • CH3CH2OH + 3O2  2CO2 + 3H2O

  32. Visual Concepts Chapter 8 Combustion Reaction

  33. Section3 Classifying Chemical Reactions Chapter 8 Synthesis Reactions • In a synthesis reaction a single compound forms from two or more reactants. • Two elements form a binary compound • C + O2 CO2 • 2C + O22CO • Two compounds form a ternary compound • CaO(s) + H2O(l)  Ca(OH)2(s) • CO2(g) + H2O(l)  H2CO3(aq)

  34. Visual Concepts Chapter 8 Synthesis Reactions

  35. Section3 Classifying Chemical Reactions Chapter 8 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 2H2O(l) O2(g)+ 2H2(g) • A metal carbonate decomposes to form a metal oxide and carbon dioxide. heat CaCO3(s) CaO(s) + CO2(g)

  36. Visual Concepts Chapter 8 Decomposition Reaction

  37. Visual Concepts Chapter 8 Electrolysis

  38. Section3 Classifying Chemical Reactions Chapter 8 Decomposition Reactions, continued Sample Problem D Predicting Products Predict the product(s) and write a balanced equation for the reaction of potassium with chlorine.

  39. Section3 Classifying Chemical Reactions Chapter 8 Decomposition Reactions, continued Sample Problem D Solution • Reaction is most likely a synthesis reaction, so the product will be binary • Potassium will lose one electron to become a 1+ ion. • Chlorine will gain one electron to become a 1– ion. • K + Cl2 KCl • Balance the equation. • 2K + Cl2 2KCl

  40. Section3 Classifying Chemical Reactions Chapter 8 Displacement Reactions • In adisplacement reactiona single element reacts with a compound and displaces another element from the compound. • 2Al(s) + 3CuCl2(aq)  2AlCl3(aq) + 3Cu(s) • Aluminum displaces copper.

  41. Visual Concepts Chapter 8 Single Displacement Reaction

  42. Section3 Classifying Chemical Reactions Chapter 8 Displacement Reactions, continued • The activity seriesranks the reactivity of elements

  43. Visual Concepts Chapter 8 Activity Series

  44. Section3 Classifying Chemical Reactions Chapter 8 Displacement Reactions, continued Sample Problem E Determining Products by Using the Activity SeriesMagnesium is added to a solution of lead(II) nitrate. Will a reaction happen? If so, write the equation and balance it.

  45. Section3 Classifying Chemical Reactions Chapter 8 Displacement Reactions,continued Sample Problem E Solution • Identify the reactants. • Magnesium will attempt to displace lead from lead(II) nitrate. • Check the activity series. • Magnesium is more active than lead and displaces it. • Write the balanced equation. • Mg + Pb(NO3)2 Pb + Mg(NO3)2

  46. Section3 Classifying Chemical Reactions Chapter 8 Double-Displacement Reactions • In adouble-displacement reactiontwo 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)

  47. Visual Concepts Chapter 8 Double-Displacement Reaction

  48. Chapter 8 • Identifying Reactions and Predicting Products

  49. Standardized Test Preparation Chapter 8 Understanding Concepts • 2. Which of these sentences correctly states the law of conservation of mass? • F. In a chemical reaction, the mass of the products cannot exceed the mass of the reactants. • G. In a chemical reaction, the mass of the products is always equal to the mass of the reactants. • H. In a chemical reaction, the mass of the products is always less than the mass of the reactants. • I. In a chemical reaction, the mass of the products is always greater than the mass of the reactants.

  50. Section4 Writing Net Ionic Equations Chapter 8 Bellringer • Write a definition for the word spectator in terms of the part spectators play in a sporting event.

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