The activation energy for radial attack is low because a new bond is formed as o
ID: 1063358 • Letter: T
Question
The activation energy for radial attack is low because a new bond is formed as one bond is lost, so once initiated the formation and consumption of radius is self-sustaining and the production of HBr is very rapid. Chain termination occurs when the radicals recombine: Termination: H^- + H^+ rightarrow H_2 Br^- + Br^- rightarrow Br_2 H^+ + Br^- rightarrow HBr Termination becomes more important towards the end of the reaction when the concentrations of H_2 and Br are low. The highly exothermic reaction of H_2 with O_2 alto occurs by a radical chain mechanism. Certain mixtures explode violently when detonated: 2 H_2 (g) + O_2 (g) rightarrow 2 H_2O(g) Delta H degree = 242 kJ mol^-1Explanation / Answer
Molecular hydrides are formed between be, p-block element and hydrogen. They are of three types:
electron precise : all the valence eelctrons of central atom forms bond with hydrogen e.g. CH4
electron rich : cental atom has more electron pair than needed for bond formation e.g. H2O, NH3
electron deficient : cental atom has less electrons than required for bond formation . e.g B2H6
Nomenclature :
The systematic naming is done by first naming theelemnet and then the suffix -ane. For example CH4, base name is met + suffix ane = methane
C2H6 : eth + ane = ethane
However, sometimes the hydrides are more known by their commertial and common names. For example NH3 is most commonly called ammonia. However its systematic name is az + ane = azane.
H2O is call water and its systematic name is ox + ane = oxane
Structures of electron rich and electron precise molecules are predicted by VSEPR. However, electron deficient molecules are very different from other as they contain 3center 2electron hydrogen bridge bonds. In B2H6 two hydrogens form two bridges between B atoms. As hydrogen is very small in size, such bond formation does not cause any setric hindrance. This type of bridge compounds are not observed for any other molecular hydrife like Al or Be and they exist as monomers (AlH3 and BeH2).
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