Chemical Energy

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Chemical Energy
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Chemical Reactions
Consider a simple reaction, Rusting. This is
a Reaction as there is a new substance is formed.
Word Equation
Iron Oxygen ? Iron Oxide
Reactants
Products
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Chemical Reactions
Chemical Equation
Number of Iron Atoms
4 Fe (s) 3O2(g) ? 2Fe203(s)
Number of Oxygen molecules
(s) solid (l) - liquid (g) gas (aq) aqueous
solution
Chemical Symbol
4
Energy Associated with chemical reactions.

• Generally, chemical reactions involve either
  absorbing energy from the surrounding environment
  (endothermic reactions) or releasing energy into
  the surrounding environment (exothermic
  reactions).
• Endothermic reactions lowers the temperature.
• Exothermic Reactions increase the temperature of
  the surroundings.

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Change of state and energy

• Condensation Freezing, (for example when liquid
  water turns into ice), is a warming process and
  hence is an exothermic process. This is because
  the energy between the liquid water molecules
  must be removed so that the ice can form. This
  energy is released in the form of heat.
• Melting Evaporation,(for example ice melting)
  is a cooling process and hence is endothermic.
  This is because extra energy must be used to
  break the bonds between the water molecules, and
  this energy comes from the surrounding area.

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Chemical Process and energy

• All chemical processes involve a transformation
• of energy from one form into another.
• For example, there are chemical reactions in
• fireworks that end up producing light (and sound)
• energy.

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Kinetic Energy
Gravitational Energy
Thermal Energy
Light Energy
Chemical Energy
All chemical processes involve a transformation
of energy.
Electrical Energy
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Airbags
Air Bags Sodium Azide ? Sodium Nitrogen
Gas 2NaN3(s) ? 2Na(s) 3N2(g)
Source -http//auto.howstuffworks.com/airbag1.htm
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The Hindenburg Disaster

• The Explosion in the Hindenburg was due to
• Hydrogen Oxygen ? water
• 2H2 (g) O2 (g) ? 2H2O (g)
• Now, airships (like the Duff Blimp) contain
  Helium, the second lightest gas. This gas is not
  reactive hence is more suitable for airships.

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Voltas Pile The First Battery.

• A combination of two different metals and a salt
  solution is called a cell. A group of cells is
  called a battery. To create Voltas battery, he
  made a stack by alternating layers of zinc,
  blotting paper soaked in salt water, and silver

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Chemical Reactions

• The Word Equation
• Zinc (s) Copper Sulphate (aq) ? Zinc Sulphate
  Copper (s)
• Using Symbols
• Zn(s) CuSO4(aq) ? ZnSO4 (aq) Cu(s)
• In this equation, the Zinc metal passes the
  electrons to the positive copper ions that are in
  the copper sulphate solution.

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Electricity from chemical change
Electron movement
G

• AIM To observe a chemical change and then use it
  to generate electricity.
• METHOD Page 68 of the textbook.

Potassium Chloride
Copper
Zinc
Bridge
Zinc Nitrate Solution
Copper Sulphate Solution.
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Daniell Cell
Source http//hyperphysics.phy-astr.gsu.edu/hbas
e/chemical/electrochem.htmlc3
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Explanation of the Daniell Cell

• As a zinc atom provides the electrons, it becomes
  a positive ion and goes into aqueous solution,
  decreasing the mass of the zinc electrode. On the
  copper side, the two electrons received allow it
  to convert a copper ion from solution into an
  uncharged copper atom which deposits on the
  copper electrode, increasing its mass. The two
  reactions are typically written
• Zn(s) - Zn2(aq) 2e-
• Cu2(aq) 2e- - Cu(s)

Source http//hyperphysics.phy-astr.gsu.edu/hbas
e/chemical/electrochem.htmlc3