Chemical Energy

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Chemical Energy

• Energy that is released via chemical reactions.
• Often times release is through combustion such as
  energy generation via coal
• Another example is a battery

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Batteries

• 3 Parts Cathode (positive charge), anode
  (negative charge) and an electrolyte (substance
  with free ions (atoms with a net charge)
• Reactions occur at the anode which release
  electrons, they want to flow toward the cathode.
• But the electrolyte keeps the electrons from
  flowing to the cathode.
• If you create a closed circuit, and provide the
  electrons an alternate path to flow to the
  cathode, then they will follow that path.
• Now the chemical reactions at the anode change
  the anode and the electrolyte chemical
  composition, and eventually they can no longer
  occur. So the battery no longer produces
  electrons and current.
• When you recharge a battery ,you reverse the flow
  of electrons through the battery and reverse the
  the chemical process, restoring the battery to
  almost its original chemical state.

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Earliest batteries-Baghdad battery

• Also called the Parthian Battery
• Artifacts discovered in 1936
• near Baghdad.
• Terracotta jar 5 inches tall, containing a
  copper rolled up copper sheet housing
  a single iron rod.
• If it were filled with an acidic liquid, it could
  produce a current
• Use as a battery is uncertain, many different
  interpretations exist.
• 
  

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Leyden Jars

• Device that stores static electricity
• Earliest form of what we now call a capacitor
• Glass jar with metal foil coating the inner and
  outer surfaces. A rod is connected to the inner
  foil and sticks out of the mouth of the jar.
• Need to be initially
  charged

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Galvanic Cells

• First attempt to derive energy from chemical
  reactions
• Consists of two metals
  (often copper and zinc) in a
  solution of a salt of the metal,
  connected by a salt bridge
  (really just a porous plate)
• Also called voltaic cells or electrochemical cells

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Voltaic pile

• First true electric battery
• Alessandra Volta first showed
  that when copper and zinc
  discs are separated by
  cardboard soaked in brine, they
  act as a galvanic cell.
• He further showed that if you stack several pairs
  of these, you get a current to flow.

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Inside a modern battery
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Leaky batteries

• Alkaline batteries-popular form of battery for
  many devices
• Uses potassium hydroxide, which is an alkaline as
  the electrolyte, instead of ammonium chloride or
  zinc chloride.
• All three are acids and can corrode the outer
  steel shell and leak.
• In addition, as a battery is discharged, Hydrogen
  as is formed, which increases the pressure inside
  the battery. This can rupture the seals on the
  ends of the battery or the battery canister
  itself.
• They create a crystalline structure on the
  outside of the battery. It can cause oxidation on
  copper leads and damages circuits.
• A solution of water and baking soda or vinegar
  can be used to attempt to clean corroded contacts.

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Lithium ion batteries

• In these batteries, lithium ions are extracted
  from the anode and inserted into the cathode to
  create a current.
• The electrolyte is often a lithium salt in a
  solution of ethylene carbonate
• Note a lithium battery is a different battery,
  it has a lithium anode-these have a longer
  lifetime and can produce higher currents and
  voltages.

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Heat Energy

• Temperature Scales
• Fahrenheit based on the height of liquid (often
  mercury or alcohol) in a glass tube.
• Celsius another scale using height of liquid in
  a tube
• Kelvin-absolute scale
• True measure of energy

• Energy associated with the random motions of the
  molecules in a medium.
• Measured by temperature

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Fahrenheit temperature scale

• Freezing point of water set at 32 and boiling
  point set at 212, so there is 180 degrees between
  them and each degree is 1/180 of the difference
  between these two points.

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Celsius temperature scale

• Freezing point of water set at 0 and boiling
  point set at 100, so there is 100 degrees between
  them and each degree is 1/100 of the difference
  between these two points.

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Kelvin temperature scale

• O K is absolute zero. All molecular motion stops.
• Interval set so that ?1 K ?1 C
• So to convert from C to K KC273
• To convert from F to K
• K (F - 32) 5/9 273

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Mass Energy

• E mc2
• Energy and mass are equivalent
• C 3 x 108 m/s.
• C is a big number and its squared! So even if m
  is small, E is big.
• A small mass, converted to energy, gives a lot of
  energy!

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Example