Balancing Equations

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Balancing Equations Types of Reactions

• CP Chem Ch 11
• with Mr. A.

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The Basics

• Just as chemical symbol can be shorthand for a
  chemical name, a balance equation can represent a
  word sentence for a reaction.
• The reactants always are found on the left and
  the products are to the right of the arrow
  representing the yield.
• Often included are the state of matter of the
  chemicals (__s__), (__l__) or (__g__) and
  (_aq__).
• Sometimes a catalyst is required to speed up the
  reaction and can be listed above the arrow.

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• Chemical symbols are the letters that make the
  words. (Br)
• Chemical Formulas are the words that make up the
  sentences. (NaBr)
• The Balance equation is the sentence which tells
  us about the chemical reaction.
• NaBr HCl ------gt NaCl HBr
• Remember, what ever goes in must come out.
• This is the Law of conservation of matter.

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Easy as Cake

• If you were to bake a cake youd need eggs,
  butter, sugar, and flour. (C, E, B, S, F)
• First youd mix the butter and sugar. (BS)
• Then combine the eggs and flour. (EF)
• Put it all together and bake
• BS EF ------gt C (BSEF)

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Icing

• Granted this is a rather simplistic example, but
  it demonstrates a point.
• It is important to remember that what goes in
  must come out.
• Hence, cake must really be BSEF or something of
  the sort and not just C.
• Each side of the equation must have the same
  number of atoms of each element.
• These atoms can rearrange locations, but can not
  magically, appear or disappear.

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The Basic Rules of Balancing

• Make sure that the chemical formulas are correct
  for the compounds.
• Reactants are on the left and Products on the
  right.
• Count the number of atoms on each side.
• Balance one element at a time by changing the
  coefficients.
• (Do not touch the subscripts!)
• Calculate and check that the number of atoms is
  correct.
• Reduce the coefficients to the smallest whole
  number number ratio.

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• AgNO3 Cu -------gt Cu(NO3)2 Ag
• Atom totals
• In Out
• Ag - Ag -
• N - N -
• O - O -
• Cu - Cu -
• NOT BALANCED!

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• ____AgNO3 ____Cu -------gt ____Cu(NO3)2
  ____Ag
• Atom totals
• In Out
• Ag - Ag -
• N - N -
• O - O -
• Cu - Cu -

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• MnO2 HCl ------gt H2O MnCl2 Cl2
• Atom totals
• In Out
• Mn - Mn -
• O - O -
• H - H -
• Cl - Cl -

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• ___MnO2 ___HCl ------gt ___H2O ___MnCl2
  ___Cl2
• Atom totals
• In Out
• Mn - Mn -
• O - O -
• H - H -
• Cl - Cl -

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An Alternative for Math Freaks!

• Rather than constantly and having to consistently
  modify the coefficients, you can solve these
  equations algebraically.
• Take the equation remove any coefficients
  (numbers) and assign a variable (a,b,c,d) to
  each unknown value.
• List each element and assign an algebraic
  equation for each element.
• So, if given (a)NaOH, then Na is 1a 1 or 2
  d.
• Use this to solve each algebraic problem for each
  variable.
• Plug in the values as the coefficients.

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__MnO2 __HCl ----gt __H2O ___MnCl2
__Cl2

• Write out the Algebra
• Mn _____ _____
• O _____ _____
• H _____ _____
• Cl _____ _____

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Apply a 1 to solve the algebra

• a 1
• 1a 1d
• _____ _____ d _____
• 2a 1c
• _____ _____ c _____
• 1b 2c
• _____ _____ b _____
• 1b 2d 2e
• _____ _____ _____ e _____

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___ H2S ___ O2 ----gt ___ SO2 ___ H2O

• H _____ _____
• S _____ _____
• O _____ _____ _____

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___ H2S ___ O2 ----gt ___ SO2 ___ H2O

• a 1
• 2a 2d d _____
• 1a 1c c _____
• 2b 2c 1d b _____

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You cant have one and a half molecules, so
double everything!

• a _____ , b _____ , c _____ , d _____
• ___ H2S ___ O2 ----gt ___ SO2 ___ H2O

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The End