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Chemical Equations & Reactions

Chemical Equations & Reactions. Chapter 8. Objectives. List observations that suggest that a chemical reaction has taken place. List three requirements for a correctly written chemical equation. Write a word equation and a formula equation for a given chemical reaction.

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Chemical Equations & Reactions

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  1. Chemical Equations & Reactions Chapter 8

  2. Objectives • List observations that suggest that a chemical reaction has taken place. • List three requirements for a correctly written chemical equation. • Write a word equation and a formula equation for a given chemical reaction. • Balance a formula equation by inspection.

  3. Chemical Reaction • Process by which one or more substances are changed into one or more different substances

  4. Indications of a Chemical Reaction • Evolution of heat & light

  5. Indications of a Chemical Reaction • Production of a gas

  6. Indications of a Chemical Reaction • Formation of a precipitate

  7. Precipitate • A solid that is produced as a result of a chemical reaction in solution & that separates from the solution

  8. Indications of a chemical reaction • Change in color. (sumac leaves change color when chlorophyll is destroyed)

  9. Chemical Equation • Representation, with symbols and formulas, of the identities and relative amounts of the reactants and products in a chemical reaction • Reactants  Products • Follows the Law of Conservation of Mass

  10. Characteristics of Chemical Equations • The equation must represent known facts • The equation must contain the correct formulas for the reactants & products • The law of conservation of mass must be satisfied- which means the same # and type of atoms are present on both sides of the equation.

  11. Word Equation Writing Chemical Equations • Represents facts- only qualitative • Example: Methane + oxygen  carbon dioxide + water

  12. Writing Chemical Equations Formula Equation Example: CH4(g) + O2(g) CO2(g) + H2O(g) (not balanced) Symbols you will see in equations pg.266

  13. Writing Chemical Equations BalancedFormula Equation • Inserting Coefficients-small whole # that appears in front of a formula • Multiplies number of atoms of each element indicated in chemical formula • Example: CH4(g) + 2O2(g) CO2(g) + 2H2O(g)

  14. Balancing Chemical Equations Balance the formula equation according to the law of conservation of mass • Balance the different types of atoms one at a time • Balance polyatomic ions that appear on both sides of the equation as single units • Balance H atoms and O atoms after atoms of all other elements have been balanced

  15. Examples Mg + HCl  MgCl2 + H2 Al2(SO4)3 + Ca(OH)2 Al(OH)3 + CaSO4 MgI2 + KNO3 KI + Mg(NO3)2

  16. Writing and Balancing Equations from Word Equations 1. Write out correct chemical formulas and symbols. 2. Balance equation. Solidaluminum metal combines with oxygen gas to produce solid aluminum oxide

  17. Writing equations from word equations • Examples to try. • Solid calcium metal reacts with water to form aqueous calcium hydroxide and hydrogen gas. • Solid iron(III)oxide and carbon monoxide gas produces solid iron and carbon dioxide gas. • Solid copper reacts with aqueous silver nitrate to produce aqueous copper (II) nitrate and solid silver.

  18. Objectives • Define & give general equations for synthesis, decomposition, single-replacement, and double-replacement reactions. • Classify a reaction as synthesis, decomposition, single displacement, double displacement or combustion. • Predict the products of simple reactions if given the reactants.

  19. 5 Basic Types of Reactions • Synthesis • Decomposition • Single-replacement • Double-replacement • Combustion

  20. Synthesis Reactions • A reaction in which two or more substances combine to form a new compound A + X  AX A and X are elements or compounds AX is a compound

  21. Synthesis Reactions • Examples: magnesium + oxygen  __________ iron + oxygen  __________ calcium oxide + water  __________ 2Mg(s) + O2(g) 2MgO(s) 2Fe(s) + O2(g) 2FeO(s) CaO(s) + H2O(l) Ca(OH)2(s)

  22. Decomposition Reactions • A reaction in which a single compound produces two or more simpler substances • Opposite of synthesis reactions AX  A + X AX is a compound A and X are elements or compounds

  23. Decomposition Reactions(Binary Compounds) • Decomposition of a binary compound into its elements. • Example: water  __________ + __________ 2H2O(l) 2H2(g) + O2(g)

  24. Electrolysis • The decomposition of a substance by an electric current

  25. Decomposition Reactions(Metal Carbonates) • Metal carbonates decompose to produce a metal oxide & carbon dioxide gas. • Example: calcium carbonate  ______ + ______ CaCO3(s) CaO(s) + CO2(g)

  26. Decomposition Reactions(Metal Hydroxides) • Metal hydroxides (except group 1 metals) decompose to produce metal oxides & water. • Example: calcium hydroxide  ______ + ______ Ca(OH)2(s) CaO(s) + H2O(g)

  27. Single-Replacement Reactions • A reaction in which one element replaces a similar element in a compound A + BX  AX + B - or – Y + BX  BY + X • A, B, X, Y are elements • AX, BX, BY are compounds

  28. Single-Replacement Reactions(Replacement of a Metal or Nonmetal) • Example: aluminum + lead nitrate  ____ + ____ fluorine + sodium chloride  ____ + ____ 2Al(s) + 3Pb(NO3)2(aq) 3Pb(s) + 2Al(NO3)3(aq) F2(g) + 2NaCl(aq) 2NaF(aq) + Cl2(s)

  29. Double-Replacement Reactions • A reaction in which the ions of two compounds exchange places in an aqueous solution to form two new compounds AX + BY  AY + BX • A, X, B, Y in reactants represent ions • AY & BX represent ionic or molecular compounds

  30. Double-Replacement Reactions(Formation of a Precipitate) • One cation of one reactant combine with the anions of another reactant to form insoluble or slightly soluble compound • Example: Potassium iodide + lead (II) nitrate  ____ + ____ 2KI(aq) + Pb(NO3)2(aq) PbI2(s) + 2KNO3(aq)

  31. Double-Replacement Reactions(Formation of a Gas) • Example: Iron(II) sulfide + hydrochloric acid  ____ + ____ FeS(s) + 2HCl(aq) H2S(g) + FeCl2(aq)

  32. Double-Replacement Reactions(Formation of Water) • Example: hydrochloric acid + sodium hydroxide  ____ + ____ HCl(aq) + NaOH(aq) NaCl(aq) + H2O(l)

  33. Combustion Reactions • A reaction in which a substance combines with oxygen, releasing a large amount of energy in the form of light and heat • Combustion of a hydrocarbon always yield carbon dioxide and water.

  34. Combustion Reactions • Example: propane + oxygen  ____ + ____ (C3H8) C3H8(g) + 5O2(g) 3CO2(g) + 4H2O(l)

  35. Try this: • Write a balanced chemical equation for the following reaction: Ethyl alcohol (C2H5OH) burns to produce carbon dioxide and water. C2H5OH + 3O2 2CO2 + 3H2O

  36. Objectives • Explain the significance of an activity series. • Use an activity series to predict whether a given reaction will occur and what the products will be.

  37. Activity Series • A list of elements organized according to the ease with which the elements undergo certain chemical reactions • Used to help predict whether certain chemical reactions will occur

  38. Activity Series • Table 8.3, p. 286 • An element can replace any element below it but not above it • Based on experiment • Will be given to you on test.

  39. Examples • Using the activity series, predict whether each of the possible reactions will occur. For the reactions that will occur, write the products & balance the equation. • Ba(s) + H2O(l) • Cu(s) + HBr(aq)  • Al(s) + HBr(aq)  • F2(g) + NaCl(s) 

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