1. Three electron acceptors ‘X’, ‘Y’ and ‘Z’ have redox potential (E₀’) of +0.15V, +0.06V and -0.1V, respectively. For a reaction

B + 2H + 2e^– à BH₂ E₀’ = +0.05V

Which of these three electron acceptors are appropriate?
[ useful equation: ΔG₀’ = -nFE₀’ ]
ΔG₀’ = free energy change;
n = number of electron
F = Faraday constant
(1) X and Y            (2) Only X
(3) Y and Z            (3) Only Z

Electron transfer reactions are fundamental to chemistry and biology, driving processes from cellular respiration to industrial catalysis. Central to these reactions is the concept of redox potential (E0’), which measures the tendency of a molecule to gain electrons. Understanding redox potentials helps determine which electron acceptors are suitable for a given reaction.

This article examines three electron acceptors—X, Y, and Z—with redox potentials of +0.15 V, +0.06 V, and -0.1 V, respectively, and evaluates their appropriateness for the reaction:

B+2H++2e−→BH2E0′=+0.05 VB+2H++2e−→BH2E0′=+0.05V

Understanding Redox Potentials and Electron Acceptors

Redox potential, expressed in volts (V), quantifies the ability of a substance to accept electrons. A higher (more positive) redox potential means a stronger affinity for electrons, making that substance a better electron acceptor.

In a redox reaction, electrons flow spontaneously from a species with lower redox potential (electron donor) to one with higher redox potential (electron acceptor). The difference in redox potentials dictates the feasibility and energy yield of the reaction.

Calculating the Feasibility of Electron Acceptors

To determine which acceptors are appropriate, we calculate the Gibbs free energy change (ΔG0’) for the electron transfer using the equation:

ΔG0′=−nFE0cell′ΔG0′=−nFE0cell′

where:

• $n=2$ (number of electrons transferred)

• $F=96,485C/mol$ (Faraday constant)

• E0cell′=E0acceptor′−E0donor′E0cell′=E0acceptor′−E0donor′

The reaction is spontaneous if ΔG0’ is negative.

Step 1: Identify Redox Potentials

Step 2: Calculate Cell Potentials (E0’cell)

E0cell′=E0acceptor′−E0donor′E0cell′=E0acceptor′−E0donor′

• For X: $0.15-0.05=+0.10V$

• For Y: $0.06-0.05=+0.01V$

• For Z: $-0.10-0.05=-0.15V$

Step 3: Calculate Gibbs Free Energy Change (ΔG0’)

ΔG0′=−nFE0cell′ΔG0′=−nFE0cell′

• For X:

ΔG0′=−2×96485×0.10=−19,297 J/mol=−19.3 kJ/molΔG0′=−2×96485×0.10=−19,297J/mol=−19.3kJ/mol

• For Y:

ΔG0′=−2×96485×0.01=−1,929.7 J/mol=−1.93 kJ/molΔG0′=−2×96485×0.01=−1,929.7J/mol=−1.93kJ/mol

• For Z:

ΔG0′=−2×96485×(−0.15)=+28,945.5 J/mol=+28.95 kJ/molΔG0′=−2×96485×(−0.15)=+28,945.5J/mol=+28.95kJ/mol

Step 4: Interpretation of Results

• Negative ΔG0’ indicates a spontaneous and energetically favorable reaction.

• Positive ΔG0’ indicates a non-spontaneous reaction.

Acceptors X and Y yield negative ΔG0’, so electron transfer from B to X or Y is spontaneous and appropriate. Acceptor Z yields a positive ΔG0’, making it unsuitable for this reaction.

Practical Implications

Selecting the right electron acceptor is critical in biochemical pathways, environmental remediation, and energy conversion technologies. Electron acceptors with higher redox potentials than the donor facilitate efficient electron transfer, maximizing energy output and reaction rates.

For example, in microbial respiration, electron acceptors with higher redox potentials enable microbes to extract more energy from substrates. Similarly, in electrochemical cells, choosing appropriate acceptors ensures optimal cell voltage and efficiency.

Summary

• Electron acceptors with redox potentials higher than the donor’s are suitable for spontaneous electron transfer.

• For the reaction B+2H++2e−→BH2B+2H++2e−→BH2 with E0′=+0.05 VE0′=+0.05V, acceptors X (+0.15 V) and Y (+0.06 V) are appropriate.

• Acceptor Z (-0.10 V) is inappropriate due to its lower redox potential, resulting in a non-spontaneous reaction.

• Gibbs free energy calculations confirm these conclusions, with ΔG0’ negative for X and Y and positive for Z.

Final Answer

The appropriate electron acceptors for the given reaction are:

(1) X and Y

Understanding redox potentials and their impact on reaction spontaneity empowers scientists and engineers to design better chemical processes, optimize biological systems, and develop innovative technologies based on electron transfer reactions.