Chemical Equations

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Chemical Equations
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Chemical Reactions

• Process where one or more substances are turned
  into one or more different substances
• A chemical change occurs
• Can be represented by a chemical equation
• A B ? C D

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Proofs of Chemical Reactions

• Creation of heat or light
• Production of a gas
• Formation of a precipitate

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Law of Conservation of Mass

• Matter is neither created nor destroyed in
  chemical reaction.
• Mass of reactants equals mass of products

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Chemical Equations

• A B ? C D

Yields
Products
Reactants
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Other Symbols

• (s) compound or element is solid
• (l) compound or element is liquid
• (g) compound or element is a gas
• (aq) compound or element is aqueous
  (dissolved in water)
• ? - reversible reaction
• Energy can be written as a reactant or product
• Either as the work energy or as a number with
  units

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Balancing Chemical Equations

• Equations must satisfy law of conservation of
  mass
• Same number of atoms of each element on each side
  of the equation
• Example
• Solid sulfur plus solid iron yields iron (III)
  sulfide
• S(s) Fe(s) ? Fe2S3 (s)
• Is this balanced?

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Coefficients

• Numbers placed in front of elements or compounds
  to balance an equation
• Different than subscripts

5 CO2
CO2
5 molecules 5 carbon atoms 10 oxygen atoms
1 molecule (no coefficient 1) 1 carbon atom 2
oxygen atoms
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Balancing Equations

• Can change coefficients but CANNOT change
  subscripts
• Example
• 3S 2 Fe ? Fe2S3

Fe2S3
S
Fe
S
Fe
S
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More Balancing Equation Examples

• Al CuO ?Al2O3 Cu
• 2Al 3CuO ? Al2O3 3Cu

Al
CuO
Al2O3
Cu
CuO
Cu
Al
CuO
Cu
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More Balancing Equation Examples

• H2 O2 ? H2O
• 2H2 O2 ? 2H2O

H2
O2
H2O
H2O
H2
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Classifying Chemical Reactions

• 5 Major Types
• Synthesis
• Decomposition
• Single Replacement
• Double Replacement
• Combustion

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Synthesis

• Means to make
• Puts together a more complex compound from
  simpler elements or compounds
• One product

A X AX
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Synthesis (cont)

• Metal/Nonmetal
• 2Na Cl2 ? 2NaCl
• Nonmetal/Nonmetal
• 2H2 O2 ? 2H2O
• PCl3 Cl2 ? PCl5

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Decomposition

• Means to break down
• Breaks down a compound into its elements
• One reactant

A X A X
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Decomposition (cont)

• 2FeCl3 ? 2Fe 3Cl2

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Single Replacement

• A single element replaces an element in a
  compound

A BY AY B AX Y AY X
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Single Replacement (cont)

• Replacement of Metals
• 3Li FeCl3 ? 3LiCl Fe
• Replacement of Halides
• 2NaCl F2 ? 2NaF Cl2

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Double Replacement

• Two compounds change partners

AX BY AY BX
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Double Displacement (cont)

• AgNO3 NaCl ? AgCl NaNO3

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Combustion

• Compounds made of C and H (hydrocarbons) react
  with O2

CXHX O2 CO2 H2O