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Electrochemistry — Chemistry STD 12 Science — Question

Gujarat BoardEnglish MediumSTD 12 ScienceChemistryElectrochemistry4 Marks
Question
Electrical work done in unit time is equal to electrical potential multiplied by total charge passed. ln order to obtain maximum work from a cell, the charge has to be passed reversibly. The reversible work done by a cell is equal to decrease in its Gibb's energy. Hence, Gibb's energy of reaction is given by
$\Delta\text{G}=\text{nFE}_\text{cell}$
Hence, Eis the emfof the cell and nFis the amount of energy.
In these questions (Q. No. i-Iv), a statement of assertion followed by a statement ofreason is given. Choose the correct answer out of the following choices.
  1. Assertion and reason both are correct statements and reason is correct explanation for assertion.
  2. Assertion and reason both are correct statements but reason is not correct explanation for assertion.
  3. Assertion is correct statement but reason is wrong statement.
  4. Assertion is wrong statement but reason is correct statement.
  1. Assertion: $\Delta\text{G}^\circ=-\text{nFE}^\circ$
Reason: E should be positive for a spontaneous reaction.
  1. Assertion: An electrochemical cell can be set up only if the red ox reaction is spontaneous.
Reason: A reaction is spontaneous if free energy change is negative.
  1. Assertion: For an electrochemical cell, $\Delta\text{G}<0$ and $\text{E}_\text{cell}>0.$
Reason: The given cell is non-spontaneous.
  1. Assertion: Current stops flowing when $E_{cell} = 0.$
Reason: Equilibrium of the cell reaction is attained.
  1. Assertion: $E_{cell}$ should have a positive value for the cell to function.
Reason: $E_{cell} = E_{cathode} - E_{anode}$
✓

Answer

  1. (b) Assertion and reason both are correct statements but reason is not correct explanation for assertion.
  1. (b) Assertion and reason both are correct statements but reason is not correct explanation for assertion.
Explanation:

If redox reaction is spontaneous, $\Delta\text{G}$ is -ve and hence, $E^\circ$ is positive.

$-\Delta\text{G}^\circ=\text{nFE}^\circ\text{cell}$
  1. (c) Assertion is correct statement but reason is wrong statement.
Explanation:

$\Delta\text{G}<0$ and $\text{E}_\text{cell}>0$ ; spontaneous.
  1. (a) Assertion and reason both are correct statements and reason is correct explanation for assertion.
  1. (b) Assertion and reason both are correct statements but reason is not correct explanation for assertion.

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