Chemistry (18BSCH03) Jan-June 2020
Module 1
Thermodynamics, Electrochemistry and corrosion
S.N Questions Marks
o
1 Write the Characteristics of Ellingham diagrams. 8
Ans: R-E diagram is a plot of ΔG versus temperature and mainly for metal oxides and sulphides.
1. Different metals & its oxides of metallurgical processes are available in R-E diagram.
2. The zero free energy is at the top of the diagram & towards down in the Y-axis is negative
value is represented.
4. Oxides or compounds which are placed at bottom of the graph indicate more negative free
energy i.e. is more stable & they reduce the less stable oxides that placed above it.
5. Change in slope indicates phase transformation from one phase to another phase.
6. Increase in slope indicates reactant undergoing phase transformation.
7. Decrease in slope indicates product undergoing phase transformation.
8. Large slope change indicates transformation from condensed phase to gaseous phase.
9. Small slope phase change indicates melting or change of solid to other phase.
10. No change in slope indicates no phase transformation.
11. Almost all oxides have negative free energy. However for noble metal case there is some
exception.
13. Upward slope of most of lines indicates that the oxides become less stable as the temperature
increases.
, 2 Explain the construction, working of Calomel electrode. 8
Calomel electrode is a metal-metal salt ion electrode. It consists of mercury, mercurous
Chloride and a solution of KCl. Mercury is
placed at the bottom of a glass tube and is
represented by Hg|Hg2Cl2|Cl-. Calomel
electrode consist of a glass bulb and
platinum wire at the center. A paste of
mercury and mercurous chloride is placed
above the mercury layer. The mercury layer
will be in contact with platinum wire. The
glass bulb will be filled with known
concentration of KCl solution. A platinum
wire is kept immersed into the mercury to
obtain electrical contact.
when it behaves as cathode
when it behaves as anode
Module 1
Thermodynamics, Electrochemistry and corrosion
S.N Questions Marks
o
1 Write the Characteristics of Ellingham diagrams. 8
Ans: R-E diagram is a plot of ΔG versus temperature and mainly for metal oxides and sulphides.
1. Different metals & its oxides of metallurgical processes are available in R-E diagram.
2. The zero free energy is at the top of the diagram & towards down in the Y-axis is negative
value is represented.
4. Oxides or compounds which are placed at bottom of the graph indicate more negative free
energy i.e. is more stable & they reduce the less stable oxides that placed above it.
5. Change in slope indicates phase transformation from one phase to another phase.
6. Increase in slope indicates reactant undergoing phase transformation.
7. Decrease in slope indicates product undergoing phase transformation.
8. Large slope change indicates transformation from condensed phase to gaseous phase.
9. Small slope phase change indicates melting or change of solid to other phase.
10. No change in slope indicates no phase transformation.
11. Almost all oxides have negative free energy. However for noble metal case there is some
exception.
13. Upward slope of most of lines indicates that the oxides become less stable as the temperature
increases.
, 2 Explain the construction, working of Calomel electrode. 8
Calomel electrode is a metal-metal salt ion electrode. It consists of mercury, mercurous
Chloride and a solution of KCl. Mercury is
placed at the bottom of a glass tube and is
represented by Hg|Hg2Cl2|Cl-. Calomel
electrode consist of a glass bulb and
platinum wire at the center. A paste of
mercury and mercurous chloride is placed
above the mercury layer. The mercury layer
will be in contact with platinum wire. The
glass bulb will be filled with known
concentration of KCl solution. A platinum
wire is kept immersed into the mercury to
obtain electrical contact.
when it behaves as cathode
when it behaves as anode
