Given E deg(Cr^3+/Cr^2+) = -0.41 V and E deg(Cr^2+/Cr) = -0.91 V, calculate E deg(Cr^3+/Cr) in volts, to two decimal places.

JEE Main levelNumerical answerDifficulty 2 of 3df071

Given $E^{\circ} (Cr X^{3 +} / Cr X^{2 +}) = - 0.41 V$ and $E^{\circ} (Cr X^{2 +} / Cr) = - 0.91 V$ , calculate $E^{\circ} (Cr X^{3 +} / Cr)$ in volts, to two decimal places.

Numerical answer type, answer in V, tolerance 0.01.

Free energies add, not potentials.

Cr X^{3 +} + e^{-} \to Cr X^{2 +}

(

n = 1

) and

Cr X^{2 +} + 2 e^{-} \to Cr

(

n = 2

) combine to a 3-electron change.

E^{\circ} = \frac{( 1 ) ( - 0.41 ) + ( 2 ) ( - 0.91 )}{3} = \frac{- 2.23}{3} = - 0.74 V

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