Chemical Reactions

1

• Chemical Reactions
• How do you know if a chemical reactions takes
  place?
• A color change takes place
• A solid (ppt) forms
• Bubbles are formed without heating
• A flame occurs
• Light or heat is given off/absorbed
• Water is produced

2
Chemical Equations

• H2SO4 2 NaOH ? Na2SO4 2 H2O
• Reactants on the left, products on the right
• ? indicates a chemical reaction
• separates the substances
• 2 coefficient - how many of that substance (big
  number out front)
• 4 subscript how many of the preceding atom
  (little numbers)

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• The 5 types of equations
• Combination (or Synthesis) A B ? AB. This
  forms a new compound from two or more reactants.
• 2 H2 O2 ? 2 H2O
• 2. Decomposition AB ? A B. A single reactant
  breaks up into two or more products. This is the
  opposite of a combination reaction.
• 2 HgO ? 2 Hg O

4

• Single Replacement
• A BX ? AX B or A BX ? BA X
• An single element replaces an element in a
  compound. A metal replaces the metal, a nonmetal
  replaces the nonmetal in the compound.
• Cl2 2 NaBr ? 2 NaCl Br2
• Cs NaCl ? CsCl Na

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4. Double Replacement AB CD ? AD CB The
positive ions in two different compounds are
swapping places, or the negative ions in two
different compounds are swapping places. H3PO4
3 NaOH ? Na3PO4 3 HOH
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5. Combustion CxHy (CxHyOz) O2 ? CO2
H2O Burning or the rapid oxidation of a carbon
compound into carbon dioxide and water. CH4 2
O2 ? CO2 2 H2O 2 CH3OH 3 O2 ? 2 CO2 4 H2O
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Tips for recognizing and balancing
reactions Combination 2 reactants ? 1
product Decomposition 1 reactant ? 2
products Single element cmpd ? element
cmpd Double elements in 2 cmpds are
exchanged Combustion CH(O) O2 ? CO2 H2O
8
Law of Conservation of Mass

• Mass can not be created or destroyed in a
  chemical reaction. It can only change form.
• This means in a chemical reaction, there must be
  the same number of each type of atom on both
  sides of the arrow.

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Balancing Equations

• Copy formulas correctly
• Subscripts can not be changed
• Change only the coefficients
• Determine the most complicated compound.
  Calculate the number of each atom/ion in that
  compound
• Go to other side of reaction, use coefficients to
  get the same number of ions
• Repeat until all ions are balanced.

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Sometimes it is easier to balance equations when
water is written as HOH, sometimes it is easier
when it is written as H2O. The coefficient of 1
is not written, it is understood. __ HCl __
Ca(OH)2 ? __ CaCl2 __ H2O This is easier to
balance if written as __ HCl __ Ca(OH)2 ? __
CaCl2 __ HOH 2 HCl Ca(OH)2 ? CaCl2 2 HOH
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• Balance the following reactions
• __Ba(NO3)2 __NaCl ? __BaCl2 __NaNO3
• __ Al __ O2 ? Al2O3
• __ C7H16 __ O2 ? __ CO2 __ H2O
• Ba(NO3)2 2 NaCl ? BaCl2 2 NaNO3
• 4 Al 3 O2 ? 2 Al2O3
• C7H16 11 O2 ? 7 CO2 8 H2O

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• If your first guess of coefficients doesnt work,
  change your guess and start over.
• Coefficient x subscript of atoms/ions
• Be consistent balance the reactions the same
  way each time.
• Be right Know when to add numbers together, and
  when to multiply numbers together.

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Predicting the products of reactions

• Identify the type of reaction combination,
  combustion or double replacement.
• Complete the reaction with the correct formulas
  based on the type of reaction.
• Balance the reaction once all of the complete
  formulas have been written.

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• To complete the reaction with correct formulas
• Combination the compound formed will be the one
  formed from the elements as ions
• Combustion the products will always be CO2 and
  H2O
• Double replacement switch the positive ions, get
  the correct formulas by cross method.
  Subscripts in the original compound dont matter
  unless they are part of the actual ion (a
  polyatomic ion).

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Changing from word problems to equations

• HOFBrINCl or Lucky 7
• Solid (s), liquid (l), gas (g), aqueous (aq)
• Write all of the correct formulas, reactants on
  the left and products on the right.
• Balance the reaction