Balancing Chemical Equations

1
Chapter 7

• Balancing Chemical Equations

2
Chemical Reaction

• Describes chemical reaction.
• Chemical equation reactants yield products

Catalyst substance that speeds up a reaction
without being used up.
3
Symbols Used

• (s) solid
• (l) liquid
• (g) gas
• (aq) aqueous (in water solution)
• gas as a product
• ppt. (precipitate)
• D means with heat
• Pt means with Platinum catalyst

4
Balancing Chemical Equations

• Balanced equations have the same of atoms of
  each element on each side of the equation.
• Law of Conservation of Mass atoms can neither
  be created nor destroyed, simply rearranged.

5
Rules for Balancing Equations

• Get the correct formulas for reactants and
  products.
• Write reactants on left, products on right and
  use plus signs and arrows when needed.
• Count the of atoms of each element in reactants
  and products.(Polyatomic ions on both sides count
  as one.)
• Balance of each element using coefficients.
• Coefficient whole in front of a formula.

6
Rules for Balancing Equations

• Check each element to make sure equation is
  balanced.
• Make sure all coefficients are in the lowest
  whole number ratio.

Do not change subscripts!!!
7
Diatomic Molecules

• Diatomic Molecules- a molecule made up two atoms
  of the same element. They are only diatomic when
  they are alone.

• There are 7 naturally occurring
• diatomic molecules.

H O N Cl Br I F
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5 Types of Reactions - 1

• Combination Reaction elements combine to form a
  compound.
• A B AB

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Examples of Combination Reactions
1. 2 Na Cl2 2 NaCl
2
2. Cu S Cu2S
3. SO3 H2O
H2SO4
4. CaO H2O
Ca(OH)2
2
MgO
5. Mg O2
2
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5 Types of Reactions - 2

• Decomposition Reaction elements break down into
  its element.
• AB A B

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Examples of Decomposition Reactions
1. 2 NaCl 2 Na Cl2
2
2
2. H2O H2 O2
2
3. HgO
Hg O2
2
Challenge Copper I Chloride Decomposes
2CuCl 2Cu Cl2
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5 Types of Reactions - 3

• Single Replacement Reaction one element
  replaces another element in a compound.
• AB C A CB
• or
• AB D AD B

-
-
- -
- -
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Reactivity Series of Metals and Non-Metals

• The single metallic element will only replace the
  metal in a compound if it is more reactive.
• A chart is used to determine if the lone metal is
  more reactive. If not, no reaction occurs.
• The single non-metallic element will only replace
  the non-metal in a compound if it is more
  reactive. The higher up in the group the
  non-metal is, the more reactive it is.

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Examples of Single Replacement Reactions
1. Zn H2SO4 ZnSO4 H2
2. K HOH KOH H2
NaCl Br2
2
2
3. Cl2 NaBr
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5 Types of Reactions - 4

• Double Replacement Reaction two compounds react
  and exchange positive ions to form two new
  compounds.
• AB CD AD CB

- -
- -
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Examples of Double Replacement Reactions
1. NaOH H2SO4 Na2SO4 HOH
2
2
2. BaCl2 K2CO3 BaCO3 KCl
2
3. FeS HCl
2
H2S FeCl2
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5 Types of Reactions - 5

• Combustion Reaction oxygen reacts with a
  compound composed of C and H.
• CxHy O2 CO2 H20

Also called Burning (exothermic) The products are
always CO2 and H2O.
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Examples of Combustion Reactions
1. C6H6 O2 CO2
H2O
3
6
7½
C6H6 O2 CO2 H2O
2 15 12
6
2. CH3OH O2 CO2 H2O
2
1½
CH3OH O2 CO2 H2O
2 3 2
4
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Special Decomposition Reactions 1

• Decomposition of a Carbonate
• XCO3 XO CO2

• ex. Na2CO3 Na2O CO2

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Special Decomposition Reactions 2

• Decomposition of a Hydroxide
• XOH XO H2O

• ex. 2NaOH Na2O H2O

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Special Decomposition Reactions 3

• Decomposition of a Chlorate
• XClO3 XCl O2

• ex. NaClO3 NaCl O2

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Special Decomposition Reactions 4

• Special single Replacement Reaction
• Group IA or IIA metal and H2O
• X HOH XOH H2

• ex. 2Na 2HOH 2NaOH H2

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How to ID types of reactions.

• Combination Reactions given 2 items that form 1
  new compound.
• Decomposition Reactions given a single compound
  that breaks into parts.
• Single Replacement given a single element plus
  a single compound, forms a new compound a a
  different element.
• Double Replacement given two compounds (s or
  s change places).
• Combustion Reaction given CH compound with
  Oxygen, always forms water and carbon dioxide.

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The End