Electrochemistry

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Electrochemical Cell

Back 1

A system which produces electrical energy.

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Oxidation

Back 2

Lose electrons

Anode

Front 3

Reduction

Back 3

Gain of electrons

Cathode

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Isolated Half Reaction

Back 4

Use equilibrium arrows

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Both reactants found on left or right

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No reaction is possible

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One reactant on left, one on right.

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Reactant highest on table must be on left (to be reduced) and reactant lowest must be on right (to be oxidized)

Spontaneous reaction

Reaction must be clockwise, farther apart will be more spontaneous.

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Disproportiation

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A redox reaction that has the same species both oxidized and reduced.

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Electrode

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A conductor at which 1/2 the reaction occurs

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Anode

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Electrode at which oxidation occurs.

Receives e-. Also gets anions as they're attracted by the +charge.

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Cathode

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Electrode where reduction occurs. E- are lost here as they are used to turn ions into atom (+ to 0). Cations travel to it ( because of e- flow). Cations use the e- to turn into an atom.

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Standard reduction potential

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A tendency of e- to flow in an electrochemical cell is called Voltage or electrical potential.

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Formula to find voltage

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E° = E°red - E°ox

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Electrochemical cell standard state

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Room temp (25°C)

Standard pressure (101.3 KPa, 1Atm)

[1M]

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Breathalyzer Chemical formula

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3C2H5OH + 2K2Cr2O7 (yellow/ orange) + 8H2SO4 ->

3CH3COOH + 2Cr2(SO4)3 (dark green) + 2K2SO4 +11H2O

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Lead-Acid Storage Battery

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Common automobile battery. Consists of alternating pairs of plates made from Pb(s) and PbO2(s)

Pro

Finding condition of battery is simple.

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Zinc-carbon battery

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Common drycell used in flashlights

Pro: cheap

Cons:

Cannot be recharged, relatively short shelf life. Voltage also decreases relatively quickly.

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Lead-Acid storage battery reaction formula

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Pb(s) + PbO2(s) + 2H+(aq) + 2HSO4-(aq) -> 2PbSO4(s) + 2H2O(l)

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Zinc-Carbon battery Chemical formula

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Cathode

2MnO2(s) + 2NH4+(aq) +2e- -> 2MnO(OH)(s) + 2NH3(aq)

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Zinc-carbon battery anode

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Zn(s) + 4NH3(aq) -> Zn(NH3)4+2(aq) + 2e-

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Alkaline Dry cell

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Very similar to the Zinc-carbon battery, and also uses MnO2 and Zn. Operates under basic conditions

Pros: much greater current and more constant Voltage than the carbon battery

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Alkaline Dry Cell cathodic reaction

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2MnO2(s) + H2O(l) + 2e- -> Mn2O3 + 2OH(aq)

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Alkaline drycell anode reaction

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Zn(s) + 2OH-(aq) -> ZnO(s) + H2O(l) + 2e-

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Fuel cell

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Device in which fuel is continuously fed into and which energy is continuously obtained.

Pros: pollution free, operates silently, and more cheaply. Operate at a higher frequency.

Cons: electrodes corrode relatively quickly. Cells require constant maintenance. Rather expensive to make. Need to be quite large in order to produce significant amounts of energy.

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Prevent corrosion (environment)

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Apply a protective layer (like paint)

Apply a metal that is corrosion resistant on the surface.

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Electrochemical protection (corrosion)

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Cathodic protection. At cathode a metal element turns into a metal ion. Attach a small chunk of metal that will oxidize more readily than the metal you want to protect. (Zn, Mg are often used)