Reactions

1
Reactions

• Equations (not the math kind - but kind of!)

2
Word Equations
What reacts and what is produced!

• Reactants - arrow - products
• Iron oxygen ---gt Iron (II) oxide
• Copper silver nitrate ---gt Silver Copper (II)
  nitrate

3
Balancing Equations
The Law

• Law of conservation of mass
• Mass of reactants mass of products
• Dont forget about the gases!
• Another way of saying this - matter is neither
  created nor destroyed!
• What does this mean?
• Try counting some atoms for some equations or
  building some models!

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Manipulatives Practice

• Define what colours are what elements eg. Red
  H, blue O
• Partner A build reactants, Partner B build
  products
• Compare - is it possible to make the reactants
  from the products and obey the LAW?
• If yes - you are balanced
• If no - you need to fix it by adding more of
  whatever molecules are needed!
• A) Si O2 --gt SiO2
• B) H2 O2 ----gt H20

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Continue

• Try this with some of the reactions on the
  Balancing Chemical Equations handout
• Avoid 6, 8, 9, 11, 14, 15 (they are more
  complex)
• If you prefer math to building models, you can
  develop your own strategy for balancing reactions

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How to Balance (without manipulatives)
Word, Skeleton, Balanced

• Write the word equation
• Change it to a skeleton equation
• Simply write the reactants and products as
  chemical formula instead of words
• Start the atom count
• To fix unbalanced atom counts, use coefficients
  in FRONT of the chemical formula to multiply it
• Continue the atom count until balanced!

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An Example

• Write the word equation
• Iron Oxygen ---gt Iron (II) oxide
• Change it to a skeleton equation
• Fe O2 --------gt FeO
• Start the atom count
• Reactants Products
• Fe 1 Fe 1
• O 2 O 1
• (Oxygens are not balanced)
• Use coefficients in FRONT of the chemical formula
  to multiply it
• Fe O2 --------gt 2 FeO
• This fixes my oxygen count, but messes up my iron
  count (see above)

2
2
2

• 2Fe O2 --------gt 2 FeO
• This second 2 fixes both of my counts! Yay Im
  done!

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Some Hints

• Put boxes around the compounds so you dont
  accidentally change them while balancing!
• Balance everything except oxygen and hydrogen
  first!!
• Treat polyatomics as one thing (replace with X)
  unless they are broken apart in the reaction
• When trying to balance 2 of something on one side
  with 3 of something on the other side, use a
  lowest common multiple approach (note this works
  with any awkward numerical combination)
• When numbers start looking impossible, sometimes
  multiplying the whole mess by 2 is a good way to
  get back on track

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Lets go practice!
Click on the picture below!
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More practice at
Or do your own search!

• http//www.chem.vt.edu/RVGS/ACT/notes/scripts/bal_
  eq1.html
• http//misterguch.brinkster.net/eqnbalance.html