Electrochemical Cells

Principles and Concepts Tues Volta

Electrochemistry: The relationship of chemical reactions with the motion of electric power (electron flow)

* The chemical reactions produce electric propulsion (galvanic cell)
* The movement of electricity produces a chemical reaction (electrolysis cell)

Electrochemical cells: a system consisting of electrodes immersed in an electrolyte solution.

1. Tues Volta / Gavalni

gambar_9_4 a. The principles of voltaic cells or galvanic cell:

* The movement of electrons in the external circuit due to redox reactions.
* Rules voltaic cell:

- There is a change: the chemical energy → electrical energy

- At the anode, electrons are the product of the oxidation reaction; anode negative poles

- At the cathode, electrons are the reactants of the reduction reaction; cathode = positive pole

- Electrons flow from anode to cathode

b. Tues concepts Volta

Tues Volta:

1. Series Volta / Nerst

a. Li, K, Ba, Ca, Na, Mg, Al, Mn, Zn, Fe Ni, Sn, Pb, (H), Cu, Hg, Ag, Pt, Au

b. Increasingly to the right, easily reduced and oxidized difficult. The more to the left, easily oxidized, the more active, and difficult to be reduced.

Principle:

1. Anode oxidation reaction occurs; cathode reduction reaction occurs
2. Electron flows: anode → cathode; electric current: the cathode → anode
3. Salt bridge: equilibrate the ions in solution

Examples of the galvanic cell:

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Cell notation: Zn / Zn +2 / / Cu +2 / Cu

/ = ½ cell potential

/ / = Potential connections Cells (cell junction potential; salt bridge)

c. Various kinds of voltaic cells

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1. Dry cell or cell Leclance

* These cells are often used for radio, tape, flashlights, toys, etc..

* The cathode as the positive terminal consists of carbon (in the form of graphite) are protected by a carbon paste, MnO2 and NH4Cl2

* Outer layer of the anode is made of zinc and appears at the bottom of the battery as the negative terminal.

* Electrolytes: A mix of pasta: MnO2 + + NH4Cl slightly Water

* The reaction is the oxidation of the zinc anode

Zn (s) → Zn2 + (aq) + 2e-

* The reaction lasted more complex cathode and a mixture of results will be formed. One of the most important reactions are:

2MnO2 (s) + 2NH4 + (aq) + 2e-→ Mn2O3 (s) + 2NH3 (aq) + H2O

* The ammonia occurs at the cathode will react with Zn2 + generated at the anode and form ion

Zn (NH3) 42 +.

2. Cell battery

* Cathode: PbO2

* Anode: Pb

* Electrolytes: H2SO4 solution

* The reaction is:

PbO2 (s) + 4H + (aq) + SO42-(aq) → PbSO4 (s) + 2H2O (cathode) Pb (s) + SO42-(aq) → PbSO4 (s) + 2e-(anode) PbO2 (s) + Pb (s) + 4H + (aq) + 2SO42-(aq) → 2PbSO4 (s) + 2H2O (total)

* At the time of cell function, the concentration of sulfuric acid will be reduced because he was involved in the reaction.

* The advantage of this type of battery is that it can be recharged (recharge) to give a voltage from an external source through the process of electrolysis, the reaction:

2PbSO4 (s) + 2H2O → PbO2 (s) + Pb (s) + 4H + (aq) + 2SO42-(aq) (total)

* The disadvantage of this type of battery is, in form, he was too heavy and again it contains sulfuric acid which can be scattered when transported.

3. Fuel Cells

* Electrodes: Ni

* Electrolyte: KOH solution

* Fuel: H2 and O2

4. Battery Ni - Cd

* Also called ni-cad battery rechargeable cargo and commonly used on sensitive electronic equipment. Potential is 1.4 volts.

* Cathode: NiO2 with a little water

* Anode: Cd

* His reaction:

Cd (s) + 2OH-(aq) → Cd (OH) 2 (s) + 2e-

+ 2e-NiO2 (s) + 2H2O → Ni (OH) 2 (s) + 2OH-(aq)

* These batteries are more expensive than regular batteries.

Source : http://www.chem-is-try.org/ (Without Translation)