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Chapter 8 Chemical Equations and Reactions

Chapter 8 Chemical Equations and Reactions. 8.1 Describing Chemical Equations. Indicators of Chemical Reactions. Evolution of Heat & Light- Exothermic Production of a Gas: CO 2 , H 2 , H 2 S Formation of a Precipitate BaCl 2 (aq) + Na 2 SO 4 (aq) → 2NaCl (aq) + BaSO 4 (s).

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Chapter 8 Chemical Equations and Reactions

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  1. Chapter 8Chemical Equations and Reactions 8.1 Describing Chemical Equations

  2. Indicators of Chemical Reactions • Evolution of Heat & Light- Exothermic • Production of a Gas: CO2, H2, H2S • Formation of a Precipitate BaCl2(aq) + Na2SO4(aq) → 2NaCl (aq) + BaSO4(s)

  3. Chemical Equations • A formula equation uses symbols & formulas to represent the identities & relative amounts of reactants & products. • There are also word equations which use chemical names instead of formulas. • See p. 246 Table Reactants (s) → Products (g) Original Substances Resulting Substances State of Matter

  4. Chemical Equations • Equations must: • Represent known facts. • Contain correct formulas for all compounds. • Satisfy the law of conservation of mass.** ** This is called balancing the equation.

  5. Balancing Equations • RULE: The number and type of atoms on the left side of the equation must equal the number and type of atoms on the right • Example: H2O → H2 + O2 *not OK • missing 1 oxygen on the left side of the equation

  6. Balancing Equations Sodium + Chlorine → Sodium Chloride Na (s) + Cl2(g) → NaCl (s) 1 2 1 1 Na Cl Na Cl

  7. Balancing Equations Sodium + Chlorine → Sodium Chloride 2Na (s) + Cl2(g) → 2NaCl (s) Must be the smallest Ratio! 2 2 2 2 Na Cl Na Cl Add coefficients to the front of a formula! 2 Na : 1 Cl2 : 2 NaCl

  8. Coefficients vs. Subscripts CH4 + 2O2→ CO2 + 2H2O • NEVER change subscript, only the coefficient when balancing!!! Subscript Coefficient

  9. Steps for Balancing Equations • Identify the names of reactants and products, and write a word equation. • Write a formula equation by substituting correct formulas for the names of the reactants and the products. • Balance the formula equation according to the law of conservation of mass. • Count atoms on both sides to be sure that the equation is balanced!

  10. Balancing Equations • The coefficients indicate relative amounts of substances, a ratio. H2(g) + Cl2(g)→ 2HCl (g) 1 mole H2 : 1 mole Cl2 : 2 mole HCl Now, convert the moles to mass values to indicate the relative masses!

  11. Practice • Write the Word Equation: FeS (aq) + H2SO4(aq) → FeSO4(aq) + H2S (g) Iron (II) + Sulfuric → Iron (II) + Hydrosulfuric Sulfide Acid Sulfate Acid

  12. Practice • Write the formula equation. Sodium + Carbon + Water (g)→ Sodium Hydrogen Oxide (s) Dioxide (g) Carbonate (s) Na2O (s) + CO2(g) + H2O (g)→ NaHCO3(s) • Now balance the equation! Na2O (s) + 2CO2(g) + H2O (g)→ 2NaHCO3(s) • Now…. Translate into a sentence!

  13. Chapter 8Chemical Equations and Reactions 8.2 Types of Chemical Reactions

  14. Types of Reactions • Most chemical reactions can be classified into 5 major categories: Synthesis Decomposition Single Replacement (Displacement) Double Replacement (Displacement) Combustion

  15. Synthesis (Composition) Reactions Two or more substances combine to form a new compound. A + X  AX • Reaction of elements with oxygen to form oxides • Reactions of elements with sulfur to form sulfides • Nonmetals react with oxygen to form oxides • Reactions of halogens to form salts • Active metal oxides react with water to form metallic hydroxides • Nonmetal oxides react with water to form oxyacids (acid rain)

  16. Synthesis Reactions 2 or more substances combine to form a more complex substance. • Reaction of elements with oxygen to form oxides: 4Al (s) + 3O2(g) → 2Al2O3(s) • Reactions of elements with sulfur to form sulfides: 8Ba (s) + S8(s) → 8BaS (s) ??? ???

  17. Synthesis Reactions • Nonmetals react with oxygen to form oxides: C (s) + O2(g) → CO2(g) • Reactions of halogens to form salts: 2Na (s) + Cl2(g) → 2NaCl (s) ??? ??? Multiple Reactants One Product

  18. Synthesis Reactions • Active metal oxides react with water to form metallic hydroxides: MgO (s) + H2O (l) → Mg(OH)2(s) • Nonmetal oxides react with water to form oxyacids (acid rain): SO2(g) + H2O (l) → H2SO3(aq) ??? ???

  19. Decomposition Reactions A single compound undergoes a reaction that produces two or more simpler substances AX  A + X • Decomposition of: • Binary compounds • (electric current) • Metal carbonates • Metal hydroxides • Metal chlorates • Oxyacids

  20. DecompositionAX → A + X One complex substance breaks down into simpler substances. • 2H2O (l) 2H2(g) + O2(g) • CaCO3(s) CaO (s) + CO2(g) • Ca(OH)2(s) CaO (s) + H2O (g) • 2KClO3(s) 2KCl (s) + 3O2(g) • H2CO3(aq) CO2(g) + H2O (l) ??? ???

  21. Single Replacement (Displacement) Reactions A + BX  AX + B Replacement of: BX + Y  BY + X Metals by a more active metal 2. Hydrogen in water by an active metal 3. Hydrogen in an acid by a metal 4. Halogens by more active halogens

  22. Single ReplacementA + BX → B + AXBX + Y → BY + X One element takes the place of another in a compound. • Zn (s) + CuSO4(aq) → ZnSO4(aq) + Cu (s) • Ca (s) + 2H2O (l) → Ca(OH)2(aq) + H2(g) • Zn (s) + H2SO4(aq) → ZnSO4(aq) + H2(g) • Cl2(g) + 2KBr (aq) → 2KCl (aq) + Br2(g) ??? ???

  23. Double Replacement (Displacement) Reactions The ions of two compoundsexchange placesin an aqueous solution to form two new compounds. AX + BY  AY + BX One of the compounds formed is usually a precipitate, an insoluble gas that bubbles out of solution, or a molecular compound, usually water.

  24. Produces a solid, gas or water! Ions of 2 compounds exchange places to form 2 new compounds Double ReplacementAX + BY → AY + BX BaCl2(aq) + Na2SO4(aq) → 2NaCl (aq) + BaSO4(s) FeS (aq) + H2SO4(aq) → FeSO4(aq) + H2S (g) NaOH (aq) + HCl (aq) → NaCl (aq) + H2O (l) Precipitate Gas ??? Water

  25. Combustion Reactions A substance combines with oxygen, releasing a large amount of energy in the form of light and heat. • Reactive elements combine with oxygen P4 (s) + 5O2 (g) P4O10 (s) (This is also a synthesis reaction) • The burning of natural gas, wood, gasoline C3H8 (g) + 5O2 (g) 3CO2 (g) + 4H2O (g) (The products are ALWAYS carbon dioxide & water)

  26. Chapter 8Chemical Equations and Reactions 8.3 Activity Series of the Elements

  27. Lithium • Potassium • Calcium • Sodium • Magnesium • Aluminum • Zinc • Chromium • Iron • Nickel • Lead • Hydrogen • Bismuth • Copper • Mercury • Silver • Platinum • Gold The Activity Series Decreasing Activity Metals can replace other metals, provided that they are above the metal that they are trying to replace. Metals above hydrogen can replace hydrogen in acids. Metals from sodium upward can replace hydrogen in water.

  28. Activity Series Guidelines • All metals above hydrogen displace hydrogen from hydrochloric acid or dilute sulfuric acid. HCl or H2SO4 • Metals above magnesium vigorously displace hydrogen from water. Magnesium displaces hydrogen from steam. Mg(OH)2 • Metals above silver combine directly with oxygen; those near the top do so rapidly. • Metals below mercury form oxides only indirectly. • Oxides of metals below mercury decompose with mild heating.

  29. Activity Series Guidelines • Oxides of metals below chromium easily undergo reduction to metals by heating with hydrogen. • Oxides of metals above iron resist reduction by heating with hydrogen. • Elements near the top of the series are never found free in nature. (highly reactive) • Elements near the bottom of the series are often found free in nature.(mildly reactive)

  30. The Activity Series of the Halogens Decreasing Activity • Fluorine • Chlorine • Bromine • Iodine Halogens can replace other halogens in compounds, provided that they are above the halogen that they are trying to replace. 2NaCl (s) + F2 (g)  2NaF (s) + Cl2 (g) ??? MgCl2 (s) + Br2 (g)  ??? No Reaction

  31. Complete and balance the reactions, if they will occur… Practice: SR SR S DR DR • Cu (s) + AgNO3(aq) → ? • Zn (s) + CuSO4(aq) → ? • Na2O (s) + CO2(g) + H2O (g) → ? • H2SO4(aq) + BaCl2(aq) → ? • Al2O3(s) + H2SO4(aq) → ?

  32. Complete and balance the reactions, if they will occur… Practice: SR SR S DR DR • Cu (s) + 2AgNO3(aq) → ? • Zn (s) + CuSO4(aq) → ? • Na2O (s) + 2CO2(g) + H2O (g) → ? • H2SO4(aq) + BaCl2(aq) → ? • Al2O3(s) + 3H2SO4(aq) → ? Cu(NO3)2(aq) + 2Ag (s) Cu (s) + ZnSO4(aq) 2NaHCO3(s) 2HCl (aq) + BaSO4(s) Al2(SO4)3(aq) + 3H2O (l)

  33. Complete and balance the reactions, if they will occur… Practice: • Ca (s) + H2O (l)→ ? • KClO3(s) → ? • MgCl2(s) + Zn (s) → ? • Al (s) + HCl (g) → ? • Cd (s) + O2(g) → ? • I2 (s) + KF (g) → ? SR D SR SR S SR

  34. Complete and balance the reactions, if they will occur… Practice: Ca(OH)2(aq) + H2(g) • Ca (s) + 2H2O (l)→ ? • 2KClO3(s) → ? • MgCl2(s) + Zn (s) → ? • 2Al (s) + 6HCl (g) → ? • 2Cd (s) + O2(g) → ? • I2 (s) + KF (g) → ? SR D SR SR S SR 2KCl (s) + 3O2(g) NR 2AlCl3 (s) + 3H2(g) 2CdO (s) NR

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