2. CONTENTS
• Reflection of last class
• Electrode potential
• Galvanic series
• Concept of activation energy
• Gibb’s free energy
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3. Reflection of Last class
• Ask a friend sitting next to you:
• Hey! Do you know about corrosion? Let’s discuss
• What do you think how corrosion occurs?
• Is their any difference between corrosion and rust?
• What are the electrochemical components and their functions?
• Mr. _____ do you know corrosion costs classified as direct and indirect cost.
• What is this direct and indirect cost?
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4. Electrode Potential
• The potential difference, which is measured in volts (v), depends upon the particular
substances constituting the electrodes. For any electric cell, the total potential is the
sum of those produced by the reactions at the two electrodes.
• In the external circuit, the electrons will flow from the most negative point to the
most positive point.
• By convention, the current will flow in the opposite direction.
• Since the electrode potential can be either positive or negative, the electrons in the
external circuit can also be said to flow from the least positive electrode to the most
positive electrode.
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5. In ideal cell conditions
• In the case of Fe/Cu
cell electrons flow
from Fe to Cu.
• While, In Fe/Zn
electrons flow from
Zn to Fe.
Electrode Potential Is it correct if yes
which one will
corrode?
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7. Activity
Iron is connected to copper and then immersed in a solution containing both
Fe2+ and Cu2+ charge.
• Which metals corrodes?
• Write equations to describe the reactions which occurs at each electrode,
assuming each electrode has a valency of 2.
• Calculate the maximum possible potential of the resulting corrosion cell.
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9. Concept of Activation Energy • A + B C + D
• A + B AB C + D
• The minimum amount
of energy required for a
chemical reaction to take place
• Catalysts play an important role
to shift the activation curves.
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10. Gibb’s Free Energy
• The driving force for metallic corrosion is the Gibbs energy change, ∆G,
which is the change in free energy of the metal and environment.
• For spontaneous reactions ∆G for the process must be negative.
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11. Activity
Express the standard electrode potential ∆E of a metal in terms of Gibbs free
energy change ∆G. Hence calculate the value of ∆G at standard temperature
and pressure for the corrosion of various metals, assuming a divalent
reaction. Also compare which one is spontaneous and more susceptible to
corrosion.
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