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

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

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

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

Common Electrochemical Cells

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.

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

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