This set of Corrosion Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Modern Theory Principles – Thermodynamics – 1”.
1. Which of the following is/are the applications of modern electrode kinetic principles?
a) Anodic protection
b) Noble metal alloying
c) Methods to measure corrosion rates rapidly
d) Anodic protection, noble metal alloying and methods to measure corrosion rates rapidly
View Answer
Explanation: Modern electrode kinetics deals with electrochemical corrosion of aqueous solution and it results in the applications of
2. What is the direct measure of work capacity or electrical energy available from a system?
a) Change in enthalpy
b) Change in Gibbs free energy
c) Reaction time
d) Concentration of reactants
View Answer
Explanation: Change is Gibbs free energy is the difference of free energies of the reaction products and reactants. And it is a direct measure of the work capacity or maximum electrical energy available in from a system.
3. If the transition of a system from one state to another state resulted in negative free energy change then it is known as a spontaneous reaction.
a) True
b) False
View Answer
Explanation: If the transition of a system from one state to another state resulted in negative free energy change then it is known as a spontaneous reaction. It means the free energy of products is less than the free energy of reactants.
4. Which of the following is true, if the transition of a system results in positive Gibbs free energy change?
a) It is a spontaneous reaction
b) Free energy of products is less
c) It is a non-spontaneous reaction
d) Free energy of reactants is more
View Answer
Explanation: If the transition of a system from one state to another state resulted in positive free energy change then it is known as a non-spontaneous reaction. It means the free energy of reactants is less than the free energy of products. It requires external heat or force to proceeds with the reaction.
5. Which of the following is a spontaneous reaction?
a) Production of ammonia
b) Corrosion of metals
c) Photosynthesis reaction
d) Generation of oxygen from water
View Answer
Explanation: Spontaneous reaction is a reaction in which the reactants convert into products without any supply of external energy. Oxidation of metal atoms into metal ions due to the instability of metallic atoms is known as the corrosion of metals.
6. The change in Gibbs free energy is a path function and it is independent of the state of the system.
a) False
b) True
View Answer
Explanation: The change in Gibbs free energy is a state function and it is independent of the path followed by the system to reach that state. It is denoted by ΔG (delta G).
7. Which of the following formula is used to calculate the Gibbs free energy of an electrochemical reaction?
a) ΔG=-nFE0cell
b) ΔG=+nFE0cell
c) ΔG=-nFEcell
d) ΔG=+nFEcell
View Answer
Explanation: ΔG=-nFEcell where n is the electrons participated in the reaction, F is the faraday constant (96500 coulombs), Ecell is the overall cell potential and E0cell is the standard cell potential.
8. What is the change in Gibb’s free energy of a Cu-Zn system with a cell potential of 1.10V?
a) -11.13 KJ/mol
b) +21.23 KJ/mol
c) +11.13 KJ/mol
d) -21.23 KJ/mol
View Answer
Explanation: Given, Cell potential = 1.10V
n=number of electrons involved in reaction = 2
F=96500 coulombs
We know, ΔG=-nFEcell
ΔG=-2*96500*1.10
ΔG=-21.23 KJ/mol
9. Which of the following is/are correct regarding the given figure?
a) It is a reversible cell with unit activity
b) Copper and zinc are cathode and anode respectively
c) It is a reversible cell of Cu-Zn system with standard cell potential of 1.10V, copper and zinc are cathode and anode respectively
d) The standard cell potential is 1.10V
View Answer
Explanation: Given figure represents a Cu-Zn system with standard (25°C, 1atm) cell potential of 1.10V. Copper and Zinc are cathode and anode respectively. Whereas two half-cells are separated by a porous membrane.
10. What are the cathodic and anodic reactions respectively of a given Cu-Zn system?
a) Cu==>Cu+2+2e and Zn+2+2e==>Zn
b) Cu+2+2e==>Cu and Zn==>Zn+2+2e
c) Cu==>Cu+2+2e and 2Zn+1+2e==>2Zn
d) Cu+2+2e==>Cu and 2Zn==>2Zn+1+2e
View Answer
Explanation: As the standard hydrogen potential of copper (+0.34V) is relatively higher than standard hydrogen potential of zinc (-0.76V) it acts as cathode and zinc act as anode.
Cathodic reaction is Cu+2+2e==>Cu
Anodic reaction is Zn==>Zn+2+2e
11. What is the overall standard cell potential of a given Cu-Fe system?
a) +0.78V
b) -0.14V
c) -0.78V
d) +0.14
View Answer
Explanation: In Cu-Fe system, copper (E0=+0.34V) acts as cathode and iron will acts as anode (E0=-0.44V). Standard cell potential of a system can be calculated using E0cell=E0cathode–E0anode. Therefore, overall standard cell potential of given Cu-Fe system is 0.34 – (-0.44) = 0.78V.
12. Which of the following metal is used as a solid interface for hydrogen gas in the standard hydrogen electrode?
a) Copper
b) Zinc
c) Gold
d) Platinized platinum
View Answer
Explanation: Platinized platinum metal is used as the solid interface for hydrogen gas in the standard hydrogen electrode. It is due to the inertness of the metal and ease with which electron transfer occurs on its surface. Platinized platinum is black platinum-coated platinum.
13. What is the Nernst equation for chemical reaction nA + mB ==> pC + qD at temperature T?
a) E=E0+2.3(RT/nF)log{([A]n+[B]m)/([C]p+[D]q)}
b) E=2.3(RT/nF)log{([A]n+[B]m)/([C]p+[D]q)}
c) E=E0+2.3(RT/nF)log{([n]A+[m]B)/([p]C+ [q]D)}
d) E=2.3(RT/nF)log{([n]A+[m]B)/([p]C+ [q]D)}
View Answer
Explanation: Nernst equation for given chemical reaction nA + mB ==> pC + qD is E=E0+2.3(RT/nF)log{([A]n+[B]m)/([C]p+[D]q)} where A and B are reactants, C and D are products and m,n,p and q are the number of moles respectively.
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