Give reasons for the following:

(i)    Transition elements and their compounds act as catalysts.

(ii)     E^{\circ} value for \left ( Mn^{2+}/Mn \right ) is negative whereas for \left ( Cu^{2+}/Cu \right ) is positive.

(iii)     Actinoids shows irregularities in their electronic confriguration.

 

 

 

 
 
 
 
 

Answers (1)
S Sumit

(i) The different reasons as to why transition elements act as catalysts are given as follows:

    (a) Due to the presence of unpaired electrons in their incomplete d - orbitals and hence possess the capacity to absorbs and re - emit wide range of energies. This makes the required energy of activation available.

     (b) In number of cases the transition metal provides a suitable large surface area with free valencies on which the reactants are absorbed.

(ii) E^{\circ} value for Mn^{2+}/Mn is negative due to extra stability of half filled 3d- orbitals of Mn^{2+}(3d^{5}) whereas E^{\circ} value for Cu^{2+}/Cu is positive because the high energy to transform \left [ Cu\rightarrow Cu^{2+} \right ] is not balanced by low hydration energy.

(iii) The irregularities in the electronic configuration of the actinoids is due to the extra stability of the f^{\circ},f^{5}and f^{10} in 5-f orbitals.

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