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Electrochemistry question

2024 · Q140
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Electrochemistry question

2024 · Q140

NEETChemistryElectrochemistryMCQ+4 / −1

The standard cell potential of the following cell Zn∣Zn2+(aq)∣Fe2+(aq)∣Fe\mathrm{Zn}\left|\mathrm{Zn}^{2+}(\mathrm{aq})\right| \mathrm{Fe}^{2+}(\mathrm{aq}) \mid \mathrm{Fe}Zn​Zn2+(aq)​Fe2+(aq)∣Fe is 0.32 V0.32 \mathrm{~V}0.32 V. Calculate the standard Gibbs energy change for the reaction:

Zn(s)+Fe2+(aq)→Zn2+(aq)+Fe(s)\mathrm{Zn}(\mathrm{s})+\mathrm{Fe}^{2+}(\mathrm{aq}) \rightarrow \mathrm{Zn}^{2+}(\mathrm{aq})+\mathrm{Fe}(\mathrm{s})Zn(s)+Fe2+(aq)→Zn2+(aq)+Fe(s)

(Given : 1 F=96487C1 \mathrm{~F}=96487 \mathrm{C}1 F=96487C)

  1. A
    −61.75 kJ mol−1-61.75 \mathrm{~kJ} \mathrm{~mol}^{-1}−61.75 kJ mol−1
  2. B
    +5.006 kJ mol−1+5.006 \mathrm{~kJ} \mathrm{~mol}^{-1}+5.006 kJ mol−1
  3. C
    −5.006 kJ mol−1-5.006 \mathrm{~kJ} \mathrm{~mol}^{-1}−5.006 kJ mol−1
  4. D
    +61.75 kJ mol−1+61.75 \mathrm{~kJ} \mathrm{~mol}^{-1}+61.75 kJ mol−1
View written solutionFree

Correct answer: A

To find the standard Gibbs energy change for the reaction, we can use the relationship between the standard Gibbs free energy change ($\Delta G^\circ$) and the standard cell potential ($E^\circ$) given by the following equation:

$$\Delta G^\circ = -nFE^\circ$$

Where:

  • $n$ is the number of moles of electrons transferred in the reaction.
  • $F$ is the Faraday constant ($$1 \mathrm{~F} = 96487 \mathrm{~C \cdot mol^{-1}}$$).
  • $E^\circ$ is the standard cell potential.

From the given reaction:

$$\mathrm{Zn}(\mathrm{s}) + \mathrm{Fe}^{2+}(\mathrm{aq}) \rightarrow \mathrm{Zn}^{2+}(\mathrm{aq}) + \mathrm{Fe}(\mathrm{s})$$

It can be observed that $n = 2$ because two electrons are transferred from zinc to iron.

Given data:

  • $$E^\circ = 0.32 \mathrm{~V}$$
  • $$1 \mathrm{~F} = 96487 \mathrm{C/mol}$$

Now, substitute the values into the equation:

$$\Delta G^\circ = -nFE^\circ$$

$$\Delta G^\circ = -2 \times 96487 \mathrm{~C/mol} \times 0.32 \mathrm{~V}$$

Calculate the value:

$$\Delta G^\circ = -2 \times 96487 \mathrm{~C/mol} \times 0.32 \mathrm{~V}$$

$$\Delta G^\circ = -2 \times 30875.84 \mathrm{~J/mol}$$

$$\Delta G^\circ = -61751.68 \mathrm{~J/mol}$$

Converting the units to kJ/mol:

$$\Delta G^\circ = -61.75168 \mathrm{~kJ/mol}$$

The closest answer, when rounded to two decimal places, is:

$$\Delta G^\circ = -61.75 \mathrm{~kJ/mol}$$

Therefore, the correct option is:

Option A: $$-61.75 \mathrm{~kJ} \mathrm{~mol}^{-1}$$

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