Electrochemistry

Electrochemistry : 10.1 Galvanic Cell

Electrochemistry

Study of relationship between chemical change & electric work

Oxidation

Loss of electron by species accompanied byn an increase in oxidation number

Ex:

Reduction

Gain electron by a species accompanied by a decrease number of oxidation

Ex:

Redox reaction

Process which there are net movement of electrons from one reactant to another

Also called oxidation – reduction process.

Oxidation and reduction occur at the same time.

Ex:

Oxidizing agent

Substance that accepts electron in redox reaction and undergoes decrease number of oxidation.
O.A is Fe₂O₃

Reducing agent
Substance that donate electron in redox reaction and undergoes an increase oxidation number.
Ex:

CO is an reducing agent

Three key point
Oxidation always accompany by reduction
Oxidizing agent reduced reducing agent oxidised

ELECTROCHEMICAL CELL

There are two type :

Voltaic cell

Electrolytic cell

VOLTAIC CELL

Use spontaneous reaction to generate electric energy

System does work on surrounding

All batteries contains voltaic cell

ELECTROLYTIC CELL

Use electrical energy to drive non-spontaneous reaction

Surrounding do work on system

Ex: electroplating & recovering metal from ores

ELECTRODES

Object that conduct electricity between cell and surrounding

2 electrode (anode & cathode) are dipped into electrolyte

ACTIVE ELECTRODES

Involve in half reaction

Ex: zinc (Zn), copper (Cu), Iron (Fe)

INACTIVE ELECTRODE

If no reactant or product can be uses as electrode

Ex: graphite (C), Platinum (Pt)

The electrolyte solution contain all species involved in the half – reaction

ANODE & CATHODE

Oxidation half reaction takes place at cathode

Electron given up by substance being oxidised (reducing agent) and leave the cell at anode

Reducing half reaction takes place at cathode

Electron are taken up by substance being reduced (oxidizing agent) & enters the cell at cathode

ELECTROLYTE

Mixture of ions (usually in aqueos solution) that are involved in reaction or that carry charge.

ESSENTIAL IDEA OF VOLTAIC CELL

Component of each half reaction (half – cell) are placed in a seperate container

The two half cell are joined by circuit which consist a wire and a salt bridge

OXIDATION HALF CELL

Metal bar (anode) is immersd in Zn²⁺ electrolyte
Ex: ZnSO₄

Zn is reactant in oxidation half reaction

Zn conduct electricity and release electron out of its half cell

Mass of Zn electrode decrease

REDUCTION HALF CELL

A Cu metal bar (cathode) is immersed in a Zn²⁺electrolyte

Ex: CuSO₄solution

Cu is a product in reduction half reaction

Cu conducts electricity and released electron into itself.

Mass of copper electrode increase

RELATIVE CHARGE ON ELECTRODES

Anode:

Electron flow from anode to cathode through wire

Cathode

Electron are continously generated at anode * consume at cathode

SALT BRIDGE

Contains a solution of non-reacting ion such as KCl,KNO_3, Na₂SO₄acts as liquid wire (allowing ions to flow & complete the circuit.

HOW DOES THE CELL MAINTAIN ITS ELECTRICAL NEUTRALITY

Anode Half Cell	Cathode Half Cell

Zn ²⁺ions enters the solution causing the excess of positive charge.	Cu²⁺ ions leave the solution causing the excess of negative charge
Cl^- ions from the salt bridge move into anode (Zn) half cell	K⁺ions from salt bridge move into cathode Cu half cell

CELL NOTATION

Ex : Zn(s) l Zn²⁺(aq) l l Cu²⁺(aq) l Cu(s)

Anode left, cathode right

'l' represent phase boundary

Use ',' for component that are in the same phase

Graphite l I^- (aq) l I(s) l l H⁺(aq), MnO₄^- (aq), Mn²⁺(aq) l graphite

Sometimes we specify the concentration of dissolved component

Zn(s) l Zn²⁺(1 M) l Cu²⁺(1 M) l Cu(s)

Electrode appear ait far right and left notation.

Half-cell component usually appear in the same order as in the half-reaction

Cu ²⁺ (aq) + 2^e- ------ Cu (s) (reducing)
Zn(s) ------ Zn²⁺ (aq) + 2e^- (oxidizing)

Cu ²⁺ (aq) + Zn(s) ------ Cu (s) + Zn²⁺ (aq) (overall)

Cell notation: the coefficient is not involved.

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Electrochemistry