Electrochemical &

ElectrolyticCells

Using Redox Reactions in everyday life

Uses for Redox Reaction

Electrochemical or Voltaic Cell – redox reactions that are utilized to produce electrical energy. (Ex. Batteries, fuel cells)

Electrons flow “downhill”

An electrochemical or voltaic cell can be compared to a hydro-electric power plant. In the power plant the energy of the water is harnessed as the water flows downhill.

In a electrochemical or voltaic cell, the energy of the electrons is harnessed as they flow “downhill” in terms of energy.

Electrochemical/voltaic cells are spontaneous. They are used to produce electricity.

Parts of an electrochemical cell

Cathode –the electrode where reduction occurs (Cathode and reduction both begin with a consonant.)

Anode – the electrode where oxidation occurs (Anode and oxidation both begin with a vowel).

Salt Bridge – part of a voltaic cell that prevents positiveor negative charge from building up at the electrodes. Ionsflow through the salt bridge.

How to keep them straight!

The parts of a voltaic cell

The parts identified

Electrolytic Cells

Redox reaction that uses electrical energy to

produce chemical energy.

(Ex. Electroplating, re-charging batteries)

Pumping electrons uphill

To continue the analogy to water, the electrolytic cell is like pumping water uphill, it requires energy.

In an electrolytic cell the electrons are “pumped” uphill by a power source.

Electrolytic cells are non-spontaneous. They require energy to take place.

COMPARISON OF VOLTAIC AND ELECTROLYTIC CELLS

SPONTANEOUS NON-SPONTANEOUS

One use of electrolytic cells is electroplating where electricity is used to deposit a thin layer of metal atoms

on the surface of an object.

Remember: Electrolytic cells are non-spontaneous. They require a power source to take place.

Which way do the electrons flow?

When two half cells are hooked together, how does one determine which one will be oxidized (give off electrons) and which one will be reduced (gain electrons)?

The answer to that question can be provided by Table J

– The Activity Series

Determining the direction the electrons flow in Voltaic Cells

Electrons flow from the more active metal to the less active metal

Electrons flow from the less active non-metal to the more active non-metal

A sample problemSuppose a Cu/Cu2+ half cell

and a Ag/Ag+ half cell are connected to form a battery. Which way will the electrons flow?

Based on Table J, Cu is a more active metal than Ag. Therefore, the electrons will flow from the Cu/Cu2+ half-cell to the Ag/Ag+ half-cell.

You try one!

Suppose a Fe/Fe3+ half cell and a Al/Al3+ half cell are connected to form a battery. Which way will the electrons flow?

Did you say the electrons would flow from the Al to the Fe? That’s what Table J tells us!