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Chapter 7
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Driving Forces of Reactions 1. Formation of a solid (precipitation reaction) 2. Formation of water (acid-base reaction) 3. Transfer of electrons (oxidation-reduction reaction) 4. Formation of a gas
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I. Precipitation reactions Use solubility rules to determine if a solid is formed (p.170) in the following equations KNO3 (aq)+BaCl2(aq) KCl (?) + Ba(NO3)2 (?) Na2SO4(aq)+Pb(NO3)2(aq) NaNO3 (?)+PbSO4(?) KOH(aq)+Fe(NO3)3 KNO3(?)+Fe(OH)3(?)
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Answers KNO3 (aq)+BaCl2(aq) KCl (aq) + Ba(NO3)2 (aq) This reaction will not occur because a solid is not formed Na2SO4(aq)+Pb(NO3)2(aq) NaNO3 (aq)+PbSO4(s) This chemical reaction will occur KOH(aq)+Fe(NO3)3 KNO3(aq)+Fe(OH)3(s) This chemical reaction will occur
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II Formation of Water In an acid base reaction, salt (ionic compounds) and water always form. HCl(aq) + NaOH (aq) HOH (l) + NaCl (aq) acid base water salt This is the molecular equation-represents the complete formulas of the reactants and products However, we can also write an ionic equation-where the electrolytes are represented as ions (solids and liquids are not broken up) H + (aq) +Cl - (aq)+Na + (aq) +OH - (aq) H2O(l) +Na + (aq) +Cl - (aq) We can also write a net ionic equation-take out the spectator ions (those not involved making a solid or liquid) H + (aq)+OH - (aq) H2O(l) *Na+ and Cl- are present on both sides so we take them out of the net ionic equation
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Practice Write the molecular, ionic, and net ionic equations for the following reaction Aqueous potassium chromate reacts with aqueous barium nitrate
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Answers Molecular K2CrO4 (aq) + Ba(NO3)2 BaCrO4 (s) + 2KNO3(aq) Ionic 2K +1 (aq)+CrO4 -2 (aq) + Ba +2 (aq)+2NO3 -1 (aq) BaCrO4 (s) + 2K + (aq)+2NO3 -1 (aq) Net Ionic CrO4 -2 (aq) + Ba +2 (aq) BaCrO4 (s)
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III Transfer of electrons Oxidation-loss of electrons Reduction-gain of electrons Oxidation/reduction reaction-metal/nonmetal reaction (sometimes nonmetals undergo ox/red if oxygen is a reactant) 2Na(s)+Cl2(g) 2NaCl(s) Na + Cl Na + + Cl - oxidation reduction
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IV Formation of a gas 2AlN (s) 2Al (s) + N2 (g)
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