Question

Given Standard reduction potentials for half reactions:
$A+e^{-}\to A^{-};E^0=-ve$
$B+e^{-}\to B^{-};E^0=+ve$
Which of the following statement(s) is/are true?

• A. For a spontaneous process,
  A will act as anode and B will act as cathode
• B. For a non-spontaneous process,
  A will act as anode and B will act as cathode
• C. A is easily reduced
• D. A is easily oxidised

Answer 1

Answer: (A), (D)

A is easily oxidised

Standard reduction potentials (SRP) of the half cell electrodes are calculated and arranged in a series of increasing order which is known as electrochemical series.
The standard electrode potential of $H^{+}/H_2$ couple is zero.

A positive $E^0$ signifies that it has high tendency to get reduced and the redox couple is a stronger oxidising agent than the $H^{+}/H_2$ couple.

Negative $E^0$ signifies that it has high tendency to get oxidised and the redox couple is a stronger reducing agent than the $H^{+}/H_2$ couple.

Thus, A is easily oxidised to $A^{-}$

For a spontaneous process, $E_{cell}^0$ should be a positive value.
$E_{cell}^{\circ }=\text{SRP of substance reduced}-\text{SRP of substance oxidised}$
(SRP - Standard reduction potential)

$E_{cell}^{\circ }=E_{cathode\left(red\right)}^{\circ }-E_{anode\left(red\right)}^{\circ }$
$E_{cell}^{\circ }=(+ve)-(-ve)$
$E_{cell}^{\circ }=+ve$

Thus, statement (a) and (d) are correct.