1. Chemistry AS 91393 – Redox reactions
ELECTROCHEMICAL CELLS
Chemistry AS – Redox reactions

2. DEFINITION
The process of using ELECTRICAL ENERGY to reverse a spontaneous redox reaction or to initiate a CHEMICAL REACTION is an ELECTROLYTIC CELL
The process of using a CHEMICAL reaction to produce ELECTRICAL ENERGY is a GALVANIC CELL

3. AN ELECTROCHEMICAL CELL
Electrical energy chemical reaction
e.g. an electric current in a solution of CuCl2 will produce Cu metal on one electrode, and Cl2 gas at the other.
Chemical reaction electrical energy
e.g. a reaction between copper metal/copper ions and magnesium metal/magnesium ions produces an electric potential
ELECTROLYSIS
AN ELECTROCHEMICAL CELL

4. An electrochemical cell
Salt Bridge – NaNO3 or KNO3 V
Mg metal
Cu metal
1 molL-1 Mg2+ (aq)
1 molL-1 Cu2+ (aq)
OXIDATION at the ANODE
REDUCTION at the CATHODE

5. Common Electrochemical Cells

6. HOW THEY WORK
The container in which electrolysis takes place is called an electrolytic cell. An electrolytic cell consists of an EXTERNAL POWER SUPPLY and 2 ELECTRODES (metals/graphite) immersed in a SOLUTION or molten reactant. The power supply (e.g. a battery) is a source of electrons. When a flow of electrons enters a solution of ions, the flow of charge is carried by the movement of ions in solution. ANIONS flow in the SAME direction as the electric current, CATIONS in the OPPOSITE direction. A compound that conducts electricity by a flow of ions when melted or dissolved in water is called an ELECTROLYTE.

7. DIAGRAM OF AN ELECTROLYTIC CELL
Electrons enter at the cathode
Electrons leave at the anode
REDUCTION at the CATHODE
Cathode (-)
Anode (+)
Anions
OXIDATION at the ANODE
Cations

8. QUESTIONS
Write an equation to show the reaction at the anode and the cathode of the electrolysis of brine (aqueous NaCl)
Write an equation to show the reaction at the anode and the cathode of the electrolysis of aluminium ore