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Section 1 Describing Chemical Reactions

Section 1 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.

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Section 1 Describing Chemical Reactions

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  1. 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.

  2. Visual Concepts Chapter 8 Chemical Reaction

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

  4. Visual Concepts Chapter 8 Signs of a Chemical Reaction Click below to watch the Visual Concept. Visual Concept

  5. Visual Concepts Chapter 8 Precipitate Click below to watch the Visual Concept. Visual Concept

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

  7. 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

  8. 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.

  9. 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.

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

  11. 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

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

  13. Visual Concepts Chapter 8 Chemical Equation Click below to watch the Visual Concept. Visual Concept

  14. 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

  15. 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

  16. Visual Concepts Chapter 8 Reading a Chemical Equation Click below to watch the Visual Concept. Visual Concept

  17. Visual Concepts Chapter 8 Balancing a Chemical Equation by Inspection Click below to watch the Visual Concept. Visual Concept

  18. 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.

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

  20. 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

  21. Section2 Balancing Chemical Equations Chapter 8 Reactions Conserve Mass

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

  23. 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.

  24. 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

  25. 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

  26. Visual Concepts Chapter 8 Combustion Reaction Click below to watch the Visual Concept. Visual Concept

  27. 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)

  28. Visual Concepts Chapter 8 Synthesis Reactions Click below to watch the Visual Concept. Visual Concept

  29. 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)

  30. Visual Concepts Chapter 8 Decomposition Reaction Click below to watch the Visual Concept. Visual Concept

  31. Visual Concepts Chapter 8 Electrolysis Click below to watch the Visual Concept. Visual Concept

  32. 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.

  33. 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

  34. 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.

  35. Visual Concepts Chapter 8 Single Displacement Reaction

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

  37. Visual Concepts Chapter 8 Activity Series Click below to watch the Visual Concept. Visual Concept

  38. 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.

  39. 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

  40. 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)

  41. Visual Concepts Chapter 8 Double-Displacement Reaction

  42. Visual Concepts Chapter 8 Precipitation Reaction Click below to watch the Visual Concept. Visual Concept

  43. Chapter 8 • Identifying Reactions and Predicting Products

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