Intro

Question 1

Corrosion in metals is defined as:

Answer 1

The chemical or electro-chemical reaction
between a metal & its environment.
This leads to one of three consequences:
 Removal of the metal.
 Formation of an oxide.
 Formation of another chemical compound.
 This change in the metal will be expected
if we consider the Thermodynamics
(energy state) of the system

Question 2

The First Law of Thermodynamics states:

Answer 2

‘Energy can neither be created nor destroyed’.
When a spontaneous change occurs, it must follow this
rule:
It must release free energy from the system to the
surrounding at constant temperature & pressure’.
Which is a way of stating the Second Law:
When corrosion occurs naturally it releases free energy,
as it is a spontaneous process’.

Question 3

Iron and Aluminium found in nature are called ores, what does this mean and how are they converted

Answer 3

 Chemical compounds including Oxygen, 
Carbon & other elements.
 It is necessary to extract the metal from these 
compounds before it can be used in 
fabrication.
 This requires the smelting of the ore.

Question 4

What’s the consequences of converting the ore to metal

Answer 4

The metal produced is now at a higher energy
level than the ore from which it was extracted.
 Energy is added to the system.
 A fundamental law of energy is, that all
systems try to reduce their energy level to a
minimum.
 Metals do this & therefore, obey the second
Law.
 Free energy is released.

Question 5

What type of energy is corrosion

Answer 5

Chemical energy

Question 6

What is the process of corrosion, describe an atom, positive and negative attributes

Answer 6

Knowing there is a driving force for the process,
it is necessary to consider the mechanism by
which corrosion can take place.
An atom is a positively charged nucleus orbited
by negatively charged electrons.
Negative charge of electrons is equal to the positive charge of the nucleus.
The overall charge on the atom is zero.

Question 7

What happens when an electron is added or subtracted

Answer 7

Electrons can be added to or taken from the
group that surrounds each atom.
 If so, the charge on the atom is no longer
zero.
 This condition of the atom is termed ‘ionic’.
 If an atom loses an electron it becomes a
positive ion.
 If an atom gains an electron it becomes a
negative ion.

Question 8

The first step in the corrosion process is:

Answer 8

 That metal atoms change their state.
 From being metallic (having no charge).
 To being ionic (having a charge).
 They do this by losing at least one electron
from their outer shell.
 Process of corrosion then goes on at the
atomic level.
 Each atom losing one or more electrons -
usually no more than 3 - to become an ion.

Question 9

Define anodic reaction

Answer 9

The reaction in which the metal is changed from its metallic
state to its ionic state, is known as the Anodic Reaction
This takes place at the Anode & is also known as Oxidation

The anodic reaction for iron releases two electrons

The ‘free’ electrons released in the anodic reaction must
be used up if the reaction is to proceed.

Question 10

Define cathodic reaction

Answer 10

The ‘free’ electrons released in the anodic reaction must
be used up if the reaction is to proceed.
This part of the reaction takes place at the site where
the free electrons are neutralised & is known as the
Cathodic Reaction.

Question 11

Define Reduction reactions.

Answer 11

Reactions that consume free electrons are
known as Reduction reactions.
 The free electrons are taken up by positive
ions & atoms of Oxygen in the electrolyte.
 This gives the Oxygen a negative charge.
 Oxygen readily accepts these free electrons.
 It needs eight electrons in its outer valence
shell.
 Occurs naturally with only six.

Question 12

What reaction happens at the cathode site

Answer 12

 Free Electrons move through the metal 
cathode
 to its surface.
 Negative ions form & emit free electrons into 
the electrolyte.
 They combine with other 
elements.
 Creating different compounds.

Question 13

Define corrosion and what must be present for the process to proceed

Answer 13

Corrosion is the degradation of a metal by an
electrochemical reaction with its environment.
For corrosion to take place, there must be:
 An anode.
 A cathode.
 An electrolyte.
 An electrical path between the anode &
cathode.