Chemical Equations

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Chemical Equations

• Contemporary ChemistryMrs. Coyle

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Part I Types of Chemical Equations
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Chemical Equations represent chemical
reactions

• Word Equations
• Skeleton Chemical Equations
• Balanced Chemical Equations

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Word Equations show the names of the reactants
and the products

• Reactants ? Products
• Methane Oxygen ? Carbon Dioxide Water
• The arrow (yield sign) and indicates that a
  reaction took place.

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Skeleton Chemical Equations

• The formulas of the reactants and products are
  written without indicating their relative
  amounts.
• Example
• CH4 O2? CO2 H2O

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Symbols for Physical State

• (l) liquid
• (s) solid
• (g) gas

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Using Symbols to Show Physical State

• CH4 (g) O2(g)? CO2 (g) H2O (g)

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Energy and Chemical Equations

• CH4(g)O2(g? CO2(g)H2O(g) energy

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Part II Balancing Chemical Equations
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Balanced Chemical Equations

• The chemical formulas and the relative amounts of
  the reactants and products are written.
• Example
• CH4 2O2? CO2 2H2O
• The coefficients indicate the relative amounts of
  each substance.
• Equal number of atoms of each element must appear
  on both sides of the balanced equation.

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Why does a chemical reaction have to be balanced?

• In any chemical or physical change, mass is
  neither created or destroyed
• Mass is CONSTANT
• Law of Conservation of Mass (Antoine Lavoisier)

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Combustion of MethaneCH4 2O2? CO2
2H2O
Atoms are rearranged!
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Example Decomposition of hydrogen peroxide in
the presence of a catalyst.

• Word equation
• hydrogen peroxide ? water oxygen

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Example Decomposition of hydrogen peroxide in
the presence of a catalyst.

• Skeleton equation
• H2O2 ? H2O O2

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Example Decomposition of hydrogen peroxide in
the presence of a catalyst.

• Balanced Equation
• 2H2O2 ? 2H2O O2

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Example Decomposition of hydrogen peroxide in
the presence of a catalyst.

• Balanced equation showing
• the catalyst (MnO2)
• the state of the reactants and products
• MnO2
• 2H2O2(l) ? 2H2O (l) O2 (g)