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Chemistry Lecture Notes Writing and Balancing Chemical Equations

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Chemistry Lecture Notes Writing and Balancing Chemical Equations - PowerPoint PPT Presentation


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Chemistry Lecture Notes Writing and Balancing Chemical Equations. other info. Chemical Equations. coefficients. 3H 2 ( g ) + N 2 ( g )  2NH 3 ( g ) balanced (Dalton). reactants. products. general: A( l ) + B( s ) C( g ) + D( aq ) + heat ( s ) = solid heat produced: exothermic

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slide1

Chemistry Lecture Notes

Writing and Balancing

Chemical Equations

slide3

other

info

Chemical Equations

coefficients

3H2(g) + N2(g)  2NH3(g)balanced (Dalton)

reactants

products

general:

A(l) + B(s) C(g) + D(aq) + heat

(s) = solid heat produced: exothermic

(l) = liquid heat consumed: endothermic

(g) = gas

(aq) = aqueous other info: temperature, pressure, catalyst, etc.

slide4

Balancing Chemical Equations

  • Balancing chemical equations is generally done “by inspection,” but here are some common steps:
  • Write the unbalanced equation (often it is written for you).
  • Start by balancing the most complex substance (often but not always).
  • Choose an element that appears in only one reactant and product (always).
  • Balance by adjusting the coefficients so that there are the same number of atoms of each element on both sides.
  • Balance polyatomic ions (if present) as a unit.
  • Balance the remaining atoms, usually ending with the least complex substance, using fractional coefficients if necessary.
  • If fractional coefficients have been used, multiply both sides of the equation by the denominator to obtain whole numbers.
    • Do not alter any formulas (change subscripts).
    • Do not add or delete any reactants or products.
    • Use the smallest set of whole numbers.
    • Double check to be sure there are the same number of atoms of each kind on both sides of the equation.
slide5

Balancing Chemical Equations

P4O10(s) + H2O(l)  H3PO4(aq)

Cu(s) + AgNO3(aq)  Cu(NO3)2(aq) + Ag(s)

Ca(s) + NH3(g)  CaH2(s) + Ca3N2(s)

K(s) + H2O(l)  KOH(aq) + H2(g)

The combustion of butane (C4H10)

slide6

Balancing Chemical Equations

    • Common polyatomic ions
slide7

Double Displacement Reactions

  • Double displacement (metathesis) reactions: reactions in which anions and cations exchange partners
    • general: A+B(aq) + C+D(aq)  A+D(aq) + CB(?)
    • if: CB(s) precipitate
    • CB(aq) weak electrolyte or nonelectrolyte
    • CB(g) gas
    • C+B(aq) ionic (soluble) no net reaction

net reaction

has occurred

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Double Displacement Reactions

    • Precipitate-forming reactions
  • Solubility Rules:
    • Soluble compounds
      • all salts of alkali metal ions and the NH4+ ion
      • all salts of NO3, C2H3O2, ClO4 ions
      • most salts of Cl, Br, and I ions
        • except Ag+, Pb+2, and Hg2+2 salts
      • most salts of the SO42 ion
        • except Sr+2, Ba+2, Pb+2, and Hg2+2 salts
          • (CaSO4 is slightly soluble)
    • Insoluble compounds
      • most salts of CO32, PO43, OH, O2, and S2 ions
        • except alkali metal and NH4+ salts
          • (hydroxides and sulfides of Ca2+, Sr2+, and Ba2+ are slightly to moderately soluble)
slide9

Double Displacement Reactions

    • Precipitate-forming reactions

Complete and balance the following reactions in aqueous solution, indicating the state of each reactant and product:

AgNO3 + NaBr

CuCl2 + KOH

Ba(NO3)2 + Na2SO4

Zn(C2H3O2)2 + Na2S

slide10

Double Displacement Reactions

    • Acids and bases

Arrhenius: acid - produces H3O+(aq) in water (formula starts with an H)

base - produces OH(aq) in water (OH– salts or amines)

HCl(aq) H3O+(aq) + Cl(aq) 100% dissociated

strong acid

HC2H3O2(aq) H3O+(aq) + C2H3O2(aq) 0.4% dissociated

weak acid

NaOH(aq) Na+(aq) + OH(aq) 100% strong base

NH3(aq) NH4+(aq) + OH(aq) 0.4% weak base

slide11

Double Displacement Reactions

    • Acid-base neutralization reactions

HCl(aq) + NaOH(aq)  NaCl(aq) + H2O(l)

acid base salt water (nonelectrolyte)

Complete and balance the following reactions:

HClO4(aq) + KOH(aq) 

HNO3(aq) + Ca(OH)2(aq) 

slide12

Double Displacement Reactions

    • Gas-forming reactions
  • Reactions that produce gases: H2S, NH3, CO2
  • K2S(aq) + 2HNO3(aq)  H2S(g) + 2KNO3(aq)
  • NH4Cl(aq) + KOH(aq)  NH4OH(aq) + KCl(aq)
    • but: NH4OH(aq)  NH3(g) + H2O(l)
  •  NH4Cl(aq) + KOH(aq)  NH3(g) + H2O(l) + KCl(aq)
  • Na2CO3(aq) + 2HCl(aq)  H2CO3(aq) + 2NaCl(aq)
    • but: H2CO3(aq)  CO2(g) + H2O(l)
  •  Na2CO3(aq) + 2HCl(aq)  CO2(g) + H2O(l) + 2NaCl(aq)

correct

equation

correct

equation

slide13

Double Displacement Reactions

    • Gas-forming reactions

Complete and balance the following reactions.

CuS(s) + HCl(aq) 

HCl(aq) + BaCO3(s) 

NaOH(aq) + NH4NO3(aq) 

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