The standard cell potential of the following cell is . Calculate the standard Gibbs energy change for the reaction:
(Given : )
- A
- B
- C
- D
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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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