The p-Block Elements

Question 1

Why are pentahalides more covalent than trihalides?

Higher the positive oxidation state of central atom, more will be its ploarising power which, in turn, increases the covalent character of bond formed between in central atom and the other atom.
Question 2

Why is BiH3 the strongest reducing agent amongst all the hydrides of Group 15 elements?

The reducing character of the hydrides of Group 15 elements increases from NH3  to BiH3(Bismuthine) because the reducing character depends upon the stability of the hydride.The greater the unstability of anhydride,the greater is the its reducing character.Since,the BiH3 is the least stable (because the size of central atom is greatest & therefore its tendency to form stable covalent bond with small hydrogen atom decreases,as a result the bond strength decreases) in this series,hence the reducing character increases. 
Question 3

Why is N2 less reactive at room temperature?

Dinitrogen (N2) IS formed by sharing three electron pairs between two nitrogen atoms.The two nitrogen atoms are joined by triple bond(N≡N). The nitrogen atom is very small in size ,therefore the bond length is also quite small(109.8 pm) & as a result the bond dissociation energy is quite high(946Kj / mol).This reason leads Nto be very less reactive at room temperature.
Question 4

Mention the conditions required to maximise the yield of ammonia.


Ammonia is prepared using the Haber’s process. The yield of ammonia can be maximized under the following conditions:
(i) Temperature ~ 700k.
(ii) High pressure of 200 x 105 Pa (about 200 atm).
(iii) A catalyst such as iron oxide with small amounts of K2,O and Al2O3.

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