Content Outline: Rechargeable Batteries - Electrolytic Cells (2.4)

Content Outline: Rechargeable Batteries - Electrolytic Cells (2.4)

Unit 2: Electrochemistry

Content Outline: Rechargeable Batteries - Electrolytic Cells (2.4)

Associated AP Learning Objectives: 1.6, 2.26, 3.8, 3.12, 3.13, 5.15, 6.1

Important Concepts from previous units:

1)Chemical reactions can run in both directions…forward or reverse (at one time or simultaneously…equilibrium).

2)Electricity is associated with metals, ions, and moving electrons.

3)Electron quantity, like chemical quantity, can be measured in moles.

  1. Electrolytic Cell(You know them are Rechargeable Batteries…don’t you need electricity?) “See” the term.
  1. Essentially, this is a rechargeable battery. It turns electrical energy into chemical energy.

It uses electricity (from an outlet) to “create” a Voltaic Battery.

  1. The electricity is “forcing” a non-spontaneous reaction to occur (run the reaction in reverse).

The greater electrical force is “pushing” the electrons in reverse to the origin metal.

1. The electrical force must be greater than the cell potential (volts).

  1. One side of the cell is being recharged(gaining electrons) and the other cell is be depleted (losing electrons) , so it can be used again.
  2. The whole cell is non-spontaneous (thermodynamically unflavored) and has a negative cell potential (EOCELL)
  1. Differences between Voltaic and Electrolytic cells (batteries):
  1. The anode and cathode of an electrolytic cell are connected to a direct current source (a larger battery essentially), such as an outlet; whereas, a voltaic cell is the energy source.

Electrolytic need external energy sources; voltaic do not…they are energy.

  1. The cathode and anodes are reversed in an electrolytic cells because the current (electron flow) is also reversed.
  2. Electrolytic cells = non-spontaneous reaction (thermodynamically unfavorable)

Voltaic cells = spontaneous reaction (thermodynamically favored)

  1. Additional Uses for Electrolytic Cells
  1. Electroplating
  1. This is a process, involving electricity, to make jewelry and other items.
  2. The electricity is used to reduce metal ions in a solution, so that they will be attracted (plated) on to a different metal surface.

For example, using electricity to make white gold from yellow gold and silver ions. The silver ions are reduced (accept the electrons of the electricity). They get a negative charge and are attracted to the positively charged gold jewelry.

  1. Artifact Restoration
  1. This process uses electricity and a buffered acid (resists a change in pH) to remove accumulated

corrosion from metal artifacts and treasure, such as buttons, belt buckles, coins, etc.

2. The acid is used to separate the items.

3. Then the metal artifact is soaked in an ionic solution and hooked to the cathode position of a cell.

4. The cathode wire flows from the external power source. Then electrons flow from the metal anode, also

submerged in the ionic solution.

5. The precious metal ions in the corrosion film are re-deposited back onto the coin.

6. The water of the solution is electrolyzed in gases. The gases carry away the flakes of corrosion.

  1. Electrolysis (“Lysis” means “to split”)
  1. The process of passing an electric current through a substance and causing it “to split”.

For example: water + electricity splits into H2(g) at the Cathode and O2(g) at the anode.

What if you could find a way to spontaneous use this method in conjunction with a fuel cell… endless energy from no energy… that is the ultimate goal and will change the world.

  1. Aluminum Production(Known as the Hall-Heroult Process)
  1. The process uses molten Cryolite (Na3AlF6) and molten Al2O3 mixed together at 1000OC.
  2. The aluminum ion is reduced to Aluminum metal in the electrolytic cell and collected on the cathode, as it settles out.
  1. Photosynthesis (The chloroplasts in sunlight act like a electrolytic battery/cell.)
  1. Sunlight (radiant electromagnetic energy) is used to power a photosynthesis, a non-spontaneous reaction overall.
  2. Sunlight acts as the external power source for powering the overall reaction:

6CO2 + 6H2O  C6H12O6 + O2 Must happen in the presence of sunlight, as it is the power source.

Light reaction is non-spontaneous (thermodynamically unfavorable)

Calvin Cycle is spontaneous (thermodynamically favorable)

These two reactions working together and involving energy is referred to as Energy Coupling.

  1. The end product of photosynthesis is glucose, which is an organic energy storing molecule.
  1. The energy is stored in the numerous covalent bonds associated with Hydrogen atoms. (Remember, Hydrogen can only make one bond though.)
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