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Chapter 8: Reactions and Aqueous Solutions

Chapter 8: Reactions and Aqueous Solutions. Predicting Whether a Reaction Will Occur. There are several different “driving forces” that cause chemical reactions to take place Formation of a solid Formation of water Transfer of Electrons Formation of a gas

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Chapter 8: Reactions and Aqueous Solutions

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  1. Chapter 8: Reactions and Aqueous Solutions

  2. Predicting Whether a Reaction Will Occur • There are several different “driving forces” that cause chemical reactions to take place • Formation of a solid • Formation of water • Transfer of Electrons • Formation of a gas • When two chemicals come together if any of these changes can occur a chemical reaction will occur. • You can predict whether a reaction will occur and the products that will form by considering these driving forces

  3. Reactions that form a Solid • Precipitation: the formation of a solid in a reaction • Precipitate: the solid formed by the reaction • Called a precipitation reaction

  4. Reactions that form a Solid

  5. Reactions that form a Solid Reaction of yellow potassium chromate and colorless barium nitrate. K2CrO4 (aq) + Ba(NO3)2 (aq)  ? How do we predict the products?

  6. Reactions that form a Solid • We must think about what happens in an aqueous solution… • What happens when an ionic compound dissolves in water? • Ba(NO3)2, a white solid, was dissolved in water • Ba+ and NO3- are present • K2CrO4 is dissolved in water • K+ and CrO42- are present • These are called Strong Electrolytes because each unit produces separated ions

  7. Reactions that form a Solid K2CrO4(aq) + Ba(NO3)2(aq)  Products Ba2+ CrO42- NO3- PRODUCTS K+ NO3- K+ K2CrO4 (aq) Ba(NO3)2(aq)

  8. Reactions that form a Solid • We can express the reaction in the form of the ions present 2K+(aq) + CrO42-(aq) + Ba2+(aq) + 2NO3-(aq) Products • Thus the mixed solution contains four types of ions • How can we decide what products will form?

  9. Reactions that form a Solid • We know that the reaction must form a solid with a net zero charge • So the product must contain cations and anions • Most ionic compounds contain only two types of ions • One type of cation and one type of anion

  10. Reactions that form a Solid • Possibilities • So the solid could be one of these • BaCrO4 is the solid

  11. Using Solubility Rules • Soluble: will readily dissolve in water • Insoluble: will not dissolve in water • Slightly soluble: a tiny amount will dissolve in water

  12. Predicting Products • AgNO3(aq) + KCl (aq) white solid • Ag+(aq) + NO3-(aq) + K+(aq) + Cl-(aq) • Possible ionic compounds: • AgNO3, AgCl, KNO3, KCl • Use solubility rules to determine which is the white solid • AgCl is white solid

  13. Describing Reactions in Aqueous Solutions • Molecular Equation • K2CrO4(aq) + Ba(NO3)2(aq)BaCrO4(s) + 2KNO3(aq) • Complete Ionic Equation • 2K+(aq) + CrO42-(aq) + Ba2+(aq) + 2NO3-(aq) BaCrO4(s) + 2K+(aq) + 2NO3-(aq) • Spectator Ions • 2K+(aq) and 2NO3-(aq) • Net Ionic Equation • Ba2+(aq) + CrO42-(aq) BaCrO4(s)

  14. Describing Reactions in Aqueous Solutions • Pb(NO3)2(aq) + Na2SO4(aq) PbSO4(s) + 2NaNO3(aq) • Pb2+(aq) + SO42-(aq)  PbSO4 (s) • NaCl(aq) + AgNO3(aq) AgCl(s) + NaNO3(aq) • Cl-(aq) + Ag+(aq) AgCl(s) • 3KOH(aq) + Fe(NO3)3(aq) Fe(OH)3 (s) + 3KNO3(aq) • Fe3+(aq) + 3OH-(aq) Fe(OH)3(s)

  15. Reactions that Form Water • Reactions between a strong acid and a strong base • Strong acids are strong electrolytes • HCl HCl  H+(aq) + Cl-(aq) • HNO3 H+(aq) + NO3-(aq) • Arreheniusacids produce H+ ions when dissolved in water

  16. Reactions that Form Water Each HCl Molecule dissociates when it dissolves in water H H Cl Cl Cl H H+ Cl- H+ Cl- Water Cl- H+

  17. Reactions that Form Water • Arrhenius bases produce OH- ions when dissolved in water • NaOH(s)  Na+(aq) + OH-(aq) • KOH(s)  K+(aq) + OH-(aq) • Strong bases are also strong electrolytes

  18. Reactions that Form Water • When acids and bases react they form water and a salt (an ionic compound) • In solution acids form H+ and bases form OH- • H+ + OH-  H2O • Net ionic equation for all acid-base rections • HCl(aq) + NaOH(aq) H2O(l) + NaCl(aq)

  19. Write the Complete and Net Ionic Equations for the following and identify each as either an acid-base or precipitation reaction • HNO3(aq) + KOH(aq) H2O(l) + KNO3(aq) • 2AgNO3(aq) + Na2CrO4(aq)  Ag2CrO4(s) + 2NaNO3(aq) • HBr(aq) + NaOH(aq)  H2O(l) + NaBr(aq) • Ni(NO3)2(aq) + K2CO3(aq)  NiCO3(s) + 2KNO3(aq)

  20. Reactions of Metals with Nonmetals • When a metal reacts with a non-metal an ionic compound is formed. The ions formed when the metal transfers electrons to the non-metal. The metal becomes a cation and the non-metal becomes an anion • Therefore a metal-nonmetal reaction can always be assumed to be an oxidation-reduction reaction, which involves electron transfer

  21. Reactions of Metals with Nonmetals • Ionic Compounds: compounds formed in a reaction between a metal and a non-metal • Made up of positive and negative ions • 2Na(s) + Cl2(g) 2NaCl(s) • Oxidation-Reduction Reactions-a reaction that involves the transfer of electrons • Na + Cl  Na+ + Cl- Electron-e-

  22. Reactions of Metals with Nonmetals • Oxidation: loss of electrons • Al  Al3+ + 3e- • Mg  Mg2+ + 2e- • Reduction: gain of electrons • Fe3+ + 3e- Fe • Cl + e-  Cl-

  23. Reactions of Metals with Nonmetals • 2Cs(s) + F2(g)  2CsF(s) • Ions Present in CsF? • Cs+ and F- • Which is oxidized? • Cs • Cs  Cs+ + e- • Which is reduced? • F • F + e-  F-

  24. Reactions of Metals with Nonmetals • 2Na(s) + Br2(l) 2NaBr(s) • Ions Present: Na+ + Br - • Oxidation: Na  Na+ + e- • Reduction: Br + e-  Br - • 2Ca(s) + O2(g)  2CaO(s) • Ions Present: Ca2+ + O2- • Oxidation: Ca  Ca2+ + 2e- • Reduction: O + 2e-  O2-

  25. Ways to Classify Reactions • Reactions can be classified into one of six categories determined by the driving force of the reaction • Double-displacement, acid-base, single-replacement, combustion, synthesis, decomposition

  26. Ways to Classify Reactions • Double-displacement Reactions • Undergo a double anion exchange • AB + CD  AD + CB • Precipitation reactions • K2CrO4(aq) + Ba(NO3)2(aq)BaCrO4(s) + 2KNO3(aq)

  27. Ways to Classify Reactions • Acid-Base Reactions • Involve H+ ions that ultimately form water in the products • HA + BOH  H2O(l) + BA • HCl(aq) + KOH(aq) H2O(l) + KCl(aq) • H+ + OH- H2O

  28. Ways to Classify Reactions • Single Replacement Reactions • A reaction in which a single anion is exchanged • A + BC  B + AC • Zn(s) + 2HCl(aq)  H2(g) + ZnCl2(aq)

  29. Ways to Classify Reactions • Combustion Reactions • Chemical reactions that involve oxygen and produce energy (heat) so rapidly a flame results • CH4(g) + O2(g) CO2(g) + 2H2O(g) • Used to produce heat or electricity • C3H8(g) + 5O2 3CO2(g) + 4H2O(g) • 2C8H18(l) + 25O2(g)  16CO2(g) + 18H2O(g) • C(s) + O2(g)  CO2(g)

  30. Ways to Classify Reactions • Synthesis Reactions • When a given compound is formed from simpler materials • A + B  AB • 2H2(g) + O2(g)  2H2O(l) • C(s) + O2(g)  CO2(g) • 2Na(s) + Cl2(g)  2NaCl

  31. Ways to Classify Reactions • Decomposition Reactions • A given compound is broken down into simpler substances, usually accomplished by heating or adding electric current • AB  A + B • 2H2O(l)  2H2(g) + O2(g) • 2HgO(s)  2Hg(l) + O2(g)

  32. Chemical Reactions

  33. Ways to Classify Reactions • S8(s) + 8O2(g)  8SO2 • 2Al(s) + 3Cl2(g)  2AlCl3 • BaCl2(aq) + Na2SO4(aq)  BaSO4(s) + 2NaCl • 2AlN(s)  2Al(s) + N2(g) • KOH(aq) + HCl(aq)  H2O(l) + KCl(aq) • 2C2H2(g) + 5O2(g)  4CO2(g) + H2O(l)

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