Using the standard electrode potentials given in Table 3.1, predict if the reaction between the following is feasible:
(i) Fe3+ (aq) and I- (aq)
(ii) Ag+ (aq) and Cu(s)
(iii) Fe3+(aq) and Br-(aq)
(iv) Ag(s) and Fe3+(aq)
(v) Br2 (aq) and Fe2+(aq).
(i) Fe3+ (aq) and I- (aq)
(ii) Ag+ (aq) and Cu(s)
(iii) Fe3+(aq) and Br-(aq)
(iv) Ag(s) and Fe3+(aq)
(v) Br2 (aq) and Fe2+(aq).
Solution and Explanation
(i) Fe3+(aq) + e- \(\rightarrow\) Fe2+(aq) ] × 2; \(E^0\)= +0.77 V
2I-(aq) \(\rightarrow\) I2(s) + 2e- ; \(E^0\)= -0.54 V
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2 Fe3+(aq) + 2I-(aq) \(\rightarrow\) 2Fe2+(aq) + I2(s) ; \(E^0\) = +0.23 V
Since\(E^0\) for the overall reaction is positive, the reaction between Fe3+(aq and I-(aq) is feasible.
(ii) Ag+(aq) + e- → Ag(s) ] × 2 ; \(E^0\)= +0.80 V
Cu(s) → Cu2+(aq) + 2e- ; \(E^0\)= -0.34 V
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2Ag+(aq)+ Cu(s) → 2Ag(s) + Cu2+(aq) ; \(E^0\) = +0.46 V
Since \(E^0\) for the overall reaction is positive, the reaction between Ag+(aq) and Cu(s) is feasible
(iii) Fe3+(aq)+e- → Fe2+(aq) ] × 2 ; \(E^0\) = +0.77 V
2Br-(aq) → Br2(l) + 2e- ; \(E^0\)= -1.09 V
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Since \(E^0\) for the overall reaction is negative, the reaction between Fe3+(aq) and Br-(aq)is not feasible
Ag(s) \(\rightarrow\) Ag+(aq) + e- ; \(E^0\) = -0.80 V
Fe3+(aq) + e- \(\rightarrow\) Fe2+(aq) ; \(E^0\) = +0.77 V
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Ag(s) + Fe3+(aq) \(\rightarrow\) Ag+(aq) + Fe2+(aq) ; \(E^0\) = -0.03 V
Since \(E^0\) for the overall reaction is negative, the reaction between Ag(s) and Fe3+(aq) is not feasible.
(v) Br2(aq) +2e- → 2Br-(aq) ;\(E^0\) = +1.09 V
Fe2+(aq) → Fe3+(aq) + e- ] × 2 ; \(E^0\) = - 0.77 V
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Br2(aq) + 2Fe2+(aq) → 2Br-(aq) +2Fe3+(aq) ;\(E^0\) = +0.32 V
Since\(E^0\) for the overall reaction is positive, the reaction between Br2(aq) and Fe2+(aq) is feasible.
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Concepts Used:
Electrochemical Cells
An electrochemical cell is a device that is used to create electrical energy through the chemical reactions which are involved in it. The electrical energy supplied to electrochemical cells is used to smooth the chemical reactions. In the electrochemical cell, the involved devices have the ability to convert the chemical energy to electrical energy or vice-versa.
Classification of Electrochemical Cell:
Cathode
- Denoted by a positive sign since electrons are consumed here
- A reduction reaction occurs in the cathode of an electrochemical cell
- Electrons move into the cathode
Anode
- Denoted by a negative sign since electrons are liberated here
- An oxidation reaction occurs here
- Electrons move out of the anode
Types of Electrochemical Cells:
Galvanic cells (also known as Voltaic cells)
- Chemical energy is transformed into electrical energy.
- The redox reactions are spontaneous in nature.
- The anode is negatively charged and the cathode is positively charged.
- The electrons originate from the species that undergo oxidation.
Electrolytic cells
- Electrical energy is transformed into chemical energy.
- The redox reactions are non-spontaneous.
- These cells are positively charged anode and negatively charged cathode.
- Electrons originate from an external source.