ELECTROCHEMISTRY

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INTRODUCTION

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What is this?

Battery

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No

Is it possible to run the cell without battery?

How does this cell run?

It can be explained by electrochemistry

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• It is the study of production of electricity from energy released during spontaneous chemical reactions

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and the use of electrical energy to bring about chemical transformations including non-spontaneous processes.

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• Batteries and fuel cells convert chemical energy into electrical energy.

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• Electrochemistry is important for creating new technologies that are eco-friendly because of more efficient and less pollutant.

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ELECTROCHEMICAL CELLS

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Electrochemical cells :

• A device which converts chemical energy from spontaneous redox reactions into electrical energy is called Electrochemical cell. These are also called as Galvanic or Voltaic cells.

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Electrochemical cells :

• In this device the Gibbs energy of the spontaneous redox reaction is converted into electrical energy.

i.e. ΔG = - nFE

ΔG = Gibbs free energy

n = moles of electrons

F = Faraday’s constant

E = standard cell potential

Where,

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Electrochemical cells :

Uses:

• Used for running a motor or other electrical gadgets like heater,

fan,

geysers etc.

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Electrochemical cells :

Description

Daniell cell is an example of galvanic cell.

Cell reaction :

• These reactions occur in two different portions of the Daniel cell.

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Electrochemical cells :

• The reduction half reaction occurs on the copper electrode

while the oxidation half reaction occurs on the zinc electrode. These are called half-cells or redox couples.

Description

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Electrochemical cells :

• Each Half cell consists of a metal rod (electrode) dipped into an electrolyte.

Description

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Electrochemical cells :

• The two half-cells are connected by a metallic wire through a voltmeter and a switch externally.

Description

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Electrochemical cells :

• The electrolytes of the two half-cells are connected internally through a salt bridge.

Description

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Electrochemical cells :

Reduction half reaction

Oxidation half reaction

Description

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Electrochemical cells :

Working process

• There is a tendency of metal ions from the solution to get deposited on the metal electrode trying to make it positively charged.

• At the same time, metal atoms of electrode have a tendency to go into the solution and make it negatively charged.

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Electrochemical cells :

Working process

• At equilibrium there is a separation of these two types of charges. Hence, depending on the tendencies of the two opposing reactions, the electrode may be positively charged or negatively charged with respect to the solution.

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Electrochemical cells :

Working process

• A potential difference developed between the electrode and electrolyte (solution) is called electrode potential.

• In a galvanic cell, the oxidation half-cell is called “anode” and it has negative potential with respect to the solution whereas the reduction half-cell is called “cathode” and it has positive potential with respect to the solution.

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Electrochemical cells :

Working process

Diffuse layer

Opposite charged ions

Adjacent to the surface

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Electrochemical cells :

Zinc anode

Copper cathode

Zn(NO₃)₂ solution

Cu(NO₃)₂ solution

NaNO₃

Zn²⁺

Cu²⁺

NO₃^-

NO₃^-

Zn²⁺

Cu²⁺

NO₃^-

Na⁺

Working process

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Electrochemical cells :

• Number of galvanic cells can be constructed on the same pattern of Daniel cell by taking combinations of any two different half-cells.

Working process

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1. A cell in which electric current is produced by an oxidation reduction process is called…

a) Voltaic cell

b) Reversible cell

c) Concentration cell

d) Standard cell

MCQS

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2. The function of salt bridge in an electro chemical cell is…

a) To prevent the mixing of the electrolyte in two half cells

b) To complete the circuit

c) To maintain the electrical neutrality of the two half cells

d) All the above

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3. Daniel cell is shown as…

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IUPAC CONVENTION

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IUPAC convention:

• Write the anode on the L.H.S and the cathode on the R.H.S by putting a vertical line in between the symbol of the metal and formula of the electrolyte in the solution.

• And put a double vertical line in between the solutions.

i.e.,

(Where R = Reactant & P = Product)

Anode || Cathode ⇒

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IUPAC convention:

For Example:

Cell reaction:

Cell representation:

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Write the cell reaction taking place in the cell?

Answer:

Cell reaction:

Question

EMF of cell:

(Electro Motive Force of cell)

E_cell = E_right – E_left

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Thank you…

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