For the first row transition metals the E- values are-nbsp-E- nbsp- amp- nbsp- -V nbsp- amp- nbsp- -Cr nbsp- amp- nbsp- -Mn nbsp- amp- nbsp- -Fe nbsp- amp- nbsp- -Co nbsp- amp- nbsp- -Ni nbsp- amp- nbsp- -Cu nbsp- nbsp-M-2-M- nbsp- nbsp- amp- -1-18 amp- -0-91 amp- -1-18 amp- -0-44 amp- -0-28 amp- -0-25 amp- -0-34 nbsp-Explain the irregularity in the above values-

Name: NCERT - Grade 12 - Chemistry - The d-and f-Block Elements - Q16
Uploaded: 2022-07-04T10:36:42+05:30
Description: Irregularity in nbsp; nbsp;E^⊖ nbsp; values of first row transition metals From V to Cr, nbsp;E^0 value becomes less negative because ionization energy ...

Irregularity in nbsp; nbsp;E^⊖ nbsp; values of first row transition metals From V to Cr, nbsp;E^0 value becomes less negative because ionization energy ...

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Byju's Answer

Standard XII

Chemistry

Groups

For the first...

Question

For the first row transition metals the $\rm~E^\ominus$ values are:

$\rm~\begin{matrix}
\rm~E^\ominus & \rm~V & \rm~Cr & \rm~Mn & \rm~Fe & \rm~Co & \rm~Ni & \rm~Cu \\
(\rm~M^{2+}/M) & -1.18 & -0.91 & -1.18 & -0.44 & -0.28 & -0.25 & +0.34
\end{matrix}$

Explain the irregularity in the above values.

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Solution

$\text{Irregularity in \(E^\ominus$ values of first row transition metals}\)

From $\rm~V$ to $\rm~Cr$, $\rm~E^0$ value becomes less negative because ionization energy and enthalpy of atomisation both increase.

From $\rm~Cr$ to $\rm~Mn$ it becomes more negative due to extra stability of $\rm~Mn^{2+}$ ($\rm~d^5$ configuration’s extra stability. Now From $\rm~Mn$ to $\rm~Fe$ its value again decreases due to increase in enthalpy of atomisation and I.E of $\rm~Fe$.
The irregular variation of $\rm~E^0(M^{2+}/M)$ can be explained by ionisation enthalpies $(\rm~\Delta _iH_1 + \Delta _iH_2)$ and also the sublimation enthalpies which are relatively much less for manganese and vanadium.

From $\rm~Fe$ to $\rm~Ni$ the value becomes less and less negative and in the end for $\rm~Cu$ its positive, as enthalpy of atomisation and I.E both increases.

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Similar questions

For M²⁺/M and M³⁺/M²⁺systems, the values for some metals are as follows:

Cr²⁺/Cr −0.9V

Cr³/Cr²⁺ −0.4 V

Mn²⁺/Mn −1.2V

Mn³⁺ /Mn²⁺ +1.5 V

Fe²⁺ /Fe −0.4V

Fe³⁺/Fe²⁺ +0.8 V

Use this data to comment upon:

(i) The stability of Fe³⁺ in acid solution as compared to that of Cr³⁺ or Mn³⁺and

(ii) The ease with which iron can be oxidised as compared to a similar process for either chromium or manganese metal.

Q. For

M^{2 +} / M and M^{3 +} / M^{2 +}

systems,

E^{0}

values for some metals are as follows:

C r^{2 +} (a q) + 2 e^{-} \to C r (s); E^{0} = - 0.91 V C r^{3 +} (a q) + e^{-} \to C r^{2 +} (a q); E^{0} = - 0.41 V

M n^{2 +} (a q) + 2 e^{-} \to M n (s); E^{0} = - 1.2 V M n^{3 +} (a q) + e^{-} \to M n^{2 +} (a q); E^{0} = + 1.51 V

F e^{2 +} (a q) + 2 e^{-} \to F e (s); E^{0} = - 0.44 V F e^{3 +} (a q) + e^{-} \to F e^{2 +} (a q); E^{0} = + 0.77 V

Which of the following statement is/are correct regarding the given standard reduction potentials?

Q. For

M^{2 +} / M

and

M^{3 +} / M^{2 +}

systems the

E^{\circ}

values for some metals are as follows:

$C r^{2 +} / C r$	$- 0.9 V$	$C r^{3 +} / C r^{2 +}$	$- 0.4 V$
$M n^{2 +} / M n$	$- 1.2 V$	$M n^{3 +} / M n^{2 +}$	$+ 1.5 V$
$F e^{2 +} / F e$	$- 0.4 V$	$F e^{3 +} / F e^{2 +}$	$+ 0.8 V$