The tendency of a chemical species to undergo reduction during an electrochemical reaction is indicated by the standard potential E° for the reaction. As represented generally by Reaction 1, E° measures the potential Z at which element X with oxidation number N accepts N electrons and is reduced to its elemental state.X(N) + Ne− → X(0), E° = Z voltsReaction 1In a galvanic cell, E° > 0 indicates a spontaneous reaction. Therefore, chemical species with higher positive E° values are reduced more easily than those with lower E° values.Using E° as a basis of comparison, the relative thermodynamic stabilities of different chemical species involving the same element at different oxidation states can be presented graphically using a Frost diagram. For a series of compounds containing element X, a Frost diagram plots the value of NE° for each compound against the corresponding oxidation number N of element X within the species. Frost diagrams for several species containing manganese or chlorine are shown in Figure 1.Figure 1 Frost diagrams for manganese and chlorineOn a Frost diagram, NE° is proportional to the standard Gibbs free energy ΔG° according to the relationshipΔG° = −FNE° = −nFE°Equation 1where n is the number of moles of electrons transferred during the electrochemical process and F is the Faraday constant. Free energy considerations also show that a species is prone to disproportionation if its position on the Frost diagram lies above a line connecting the points of two adjacent species, as seen for species B in Figure 2.Figure 2 General Frost diagram for an element forming species A, B, C, and D.The slope of a line segment joining two species on a Frost diagram is equal to the standard reduction potential for the couple. A greater slope indicates a higher corresponding reduction potential. As a result, in Figure 2, the reduction potential for B to A is lower than that for D to C. Question 42Based on the passage, which of the following species is LEAST likely to undergo a disproportionation reaction?A.H3MnO4, pH = 0B.MnO43−, pH = 14C.Mn3+, pH = 0D.MnO2, pH = 14
Question
The tendency of a chemical species to undergo reduction during an electrochemical reaction is indicated by the standard potential E° for the reaction. As represented generally by Reaction 1, E° measures the potential Z at which element X with oxidation number N accepts N electrons and is reduced to its elemental state.X(N) + Ne− → X(0), E° = Z voltsReaction 1In a galvanic cell, E° > 0 indicates a spontaneous reaction. Therefore, chemical species with higher positive E° values are reduced more easily than those with lower E° values.Using E° as a basis of comparison, the relative thermodynamic stabilities of different chemical species involving the same element at different oxidation states can be presented graphically using a Frost diagram. For a series of compounds containing element X, a Frost diagram plots the value of NE° for each compound against the corresponding oxidation number N of element X within the species. Frost diagrams for several species containing manganese or chlorine are shown in Figure 1.Figure 1 Frost diagrams for manganese and chlorineOn a Frost diagram, NE° is proportional to the standard Gibbs free energy ΔG° according to the relationshipΔG° = −FNE° = −nFE°Equation 1where n is the number of moles of electrons transferred during the electrochemical process and F is the Faraday constant. Free energy considerations also show that a species is prone to disproportionation if its position on the Frost diagram lies above a line connecting the points of two adjacent species, as seen for species B in Figure 2.Figure 2 General Frost diagram for an element forming species A, B, C, and D.The slope of a line segment joining two species on a Frost diagram is equal to the standard reduction potential for the couple. A greater slope indicates a higher corresponding reduction potential. As a result, in Figure 2, the reduction potential for B to A is lower than that for D to C. Question 42Based on the passage, which of the following species is LEAST likely to undergo a disproportionation reaction?A.H3MnO4, pH = 0B.MnO43−, pH = 14C.Mn3+, pH = 0D.MnO2, pH = 14
Solution
The passage states that a species is prone to disproportionation if its position on the Frost diagram lies above a line connecting the points of two adjacent species. Without the Frost diagram, we cannot directly determine which species is least likely to undergo a disproportionation reaction. However, we can make an educated guess based on the information given in the passage.
The passage also mentions that a greater slope on the Frost diagram indicates a higher corresponding reduction potential. This means that species with higher reduction potentials are more likely to undergo disproportionation.
Given the options, we can infer that MnO2 at pH=14 (D) is least likely to undergo a disproportionation reaction. This is because MnO2 is a stable compound and at a high pH, it is less likely to accept additional electrons and undergo reduction, making it less likely to disproportionation.
However, this is an educated guess and the actual answer would depend on the specific Frost diagram for manganese.
Similar Questions
The cell potential of an electrochemical cell is positive. What does that tell you about the redox reaction?A.The reduction part of the reaction occurs at the anode.B.The oxidation part of the reaction occurs at the cathode.C.The reaction is spontaneous.D.The reaction is nonspontaneous.
In an electrochemical cell:
In an electrochemical cell:a.Kinetic energy decreasesb.Potential energy decreasesc.Potential energy gets converted into electrical energyd.Chemical energy gets converted into electrochemical energy
ELECTROCHEMISTRY
Which of the following statements about galvanic cell is incorrect?anode is positiveoxidation occurs at the electrode with lower reduction potentialcathode is positive reduction occurs at cathode
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