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Chemical Reactions

Chemical Reactions. Chapter 9. Chapter Objectives. Writing Chemical Equations Balancing Chemical Equations Reactions in Aqueous Solutions Predicting if a reaction will occur Classifying chemical reactions.

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Chemical Reactions

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  1. Chemical Reactions Chapter 9

  2. Chapter Objectives • Writing Chemical Equations • Balancing Chemical Equations • Reactions in Aqueous Solutions • Predicting if a reaction will occur • Classifying chemical reactions

  3. The process by which one or more substances are rearranged to form different substances is called a chemical reaction.

  4. Chemical Reactions • Clues that a reaction has occurred • Writing Chemical Equations • Balancing Chemical Equations

  5. THINGS TO LOOK FOR IN A CHEMICAL CHANGE • Evolution of a gas a. Formation of bubbles b. A distinct odor • Formation of a precipitate, a water insoluble product • Large amounts of energy released or absorbed • A color change

  6. Chemists use statements called equations to represent chemical reactions. • Reactantsare the starting substances. • Productsare the substances formed in the reaction.

  7. Writing Chemical Equations 1.The identities of the reactants and products must be known. 2.The correct formulas of both reactants and products must be expressed. 3. The physical state of the substances may be specified for clarity.

  8. Indicating Physical States • Gas (g) • Liquid (l) • Solid (s) • Water solution (aq)

  9. In word equations, aluminum(s) + bromine(l) → aluminum bromide(s) • reads as “solid aluminum and liquid bromine react to produce solid aluminum bromide”.

  10. 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.

  11. A chemical equationis a statement that uses chemical formulas to show the identities and relative amounts of the substances involved in a chemical reaction

  12. Balancing Chemical Equations • 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.

  13. Writing balanced equations: • Methane burns in oxygen to produce carbon dioxide and water. • CH4 (g) + 2 O2 (g) CO2 (g)+ 2 H2O • Solid sodium reacts with liquid water to produce hydrogen gas and dissolved sodium hydroxide (NaOH). • 2 Na (s) + H2 (g)  2 NaOH (aq) • Molten potassium chlorate decomposes to form gaseous oxygen and solid potassium chloride. • 2 KClO3 (l) 3 O2 (g) + 2 KCl (s)

  14. In water solution, hydrochloric acid and sodium carbonate react to produce sodium chloride, water, and carbon dioxide. 2 HCl (aq) + Na2CO3 (aq) 2 NaCl (aq) + H2O (l) + CO2 (g) White phosphorus burns vigorously in air to yield diphosphoruspentaoxide. P4 (s) + 5 O2 (g) 2 P2O5 (s) Diphosphoruspentaoxide reacts vigorously in water yielding phosphoric acid. P2O5 (s) + 3 H2O (l)  2 H3PO4 (aq)

  15. Magnesium reacts with air to form both magnesium oxide and magnesium nitride. A. What is the balanced reaction forming magnesium oxide? 2 Mg (s) + O2 (g) 2 MgO (s) B. What is the balanced reaction forming magnesium nitride? 3 Mg (s) + N2 (g)  Mg3N2 (s)

  16. Magnesium nitride reacts with water forming magnesium oxide and ammonia. Mg3N2(s) + 3 H2O (g)  3 MgO(s) + 2 NH3 (aq) Butane, C4H10, reacts in air to give carbon dioxide and water. 2 C4H10 (l) + 13 O2 (g)  8 CO2 (g) + 10 H2O

  17. Types of Chemical Reactions • A + B  C • C  A + B • A + BC  AC + B • AB + CD  AD + CB • Substance X + O2 Products

  18. A + B  C Composition or Synthesis Reactions H2(g) + O2(g)  H2O(l) NH3(g) + H3PO4(aq)(NH4)3PO4(aq) P4(s) + S8(s)  P2S5(s)

  19. A synthesis reactionis a reaction in which two or more substances react to produce a single product. • Calcium oxide and water react to form calcium hydroxide. • CaO (s) + H2O Ca(OH)2 (aq) • Sulfur dioxide reacts with oxygen to form sulfur trioxide. • 2 SO2 (g) + O2 (g)  2 SO3 (g)

  20. 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.

  21. C  A + B Decomposition Reactions KClO3(s)  KCl(s) + O2(g) C12H22O11(s)  C(s) + H2O(l)

  22. Ammonium nitrate breaks down into dinitrogen monoxide and water when heated to a high temperature. • NH4(NO3)(s)  N2O (g) + 2 H2O • Sodium azide (used in air bags) decomposes producing nitrogen gas and solid sodium. (The nitrogen gas inflates the air bag.) • 2 NaN3 (s)  3 N2 + 2 Na(s)

  23. 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.) • 2 H2 (g) + O2 (g)  2 H2O

  24. Substance X + O2(g)  Products H2S(g) + O2(g)  SO2(g) + H2O(g) C6H14(l) + O2(g)  CO2(g) + H2O(l) C25H52(s) + O2(g)  CO2(g) + H2O(l) S8(s) + O2(g)  SO2(g) C26H20O10(s) + O2(g)CO2(g) + H2O(g)

  25. A reaction in which the atoms of one element replace the atoms of another element in a compound is called a singlereplacement reaction. A + BX → AX + B

  26. Single Replacement Reactions • Type 1: A metal replaces hydrogen: • Lithium metal reacts with water to form lithium hydroxide and hydrogen. • Type 2: A metal replaces another metal: • A copper bar reacts with silver nitrate to form silver metal and copper (II) nitrate.

  27. 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.

  28. Suppose you placed silver wire in aqueous copper(II) nitrate. Will the silver atoms replace the copper atoms? • No

  29. Type 3 Nonmetals replace nonmetals: • Fluorine reacts with aqueous sodium bromide to form aqueous sodium fluoride and liquid bromine.

  30. Will bromine gas react with aqueous sodium fluoride to form aqueous sodium bromide? • No

  31. Double replacement reactionsoccur when ions exchange between two compounds.

  32. 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.

  33. Sodium chloride reacts with aqueous silver nitrate to form aqueous sodium nitrate and solid silver chloride. • NaCl (s) + AgNO3 (aq)  NaNO3 (aq) + AgCl (s) • Calcium chloride reacts with aqueous aluminum sulfate to produce solid calcium sulfate and aqueous aluminum chloride. • 3 CaCl2 (s) + Al2(SO4)3 (aq)  3 CaSO4 (s) + 2 AlCl3 (aq)

  34. Reactions in Aqueous Solutions • An aqueous solutioncontains one or more dissolved substances (called solutes) in water. • The solventis the most plentiful substance in a solution.

  35. Ionic compounds can also be solutes in aqueous solutions. • When ionic compounds dissolve in water, their ions separate in a process called dissociation.

  36. When Ionic Compounds Dissolve • NaCl in water • NaCl H2O Na+(aq) + Cl–(aq)

  37. 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.

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