Properties of Hydrogen
Hydrogen is a colorless, odorless, tasteless, lightest and highly flammable gas. It is a non-polar diatomic molecule. It can be liquefied under low temperature and high pressure. Hydrogen is a good reducing agent. Various physical constants of hydrogen molecule are listed in Table 4.1.
Hydrogen reacts with oxygen to give water. This is an explosive reaction and releases lot of energy. This is used in fuel cells to generate electricity.
2 H2 + O2 → 2 H2O
Similarly, hydrogen also reacts with halogens to give corresponding halides. Reaction with fluorine takes place even in dark with explosive violence while with chlorine at room temperature under light. It combines with bromine on heating and reaction with iodine is a photochemical reaction.
H2 + X2 → 2 HX (X = F, Cl, Br & I)
In the above reactions the hydrogen has an oxidation state of +1. It also has a tendency to react with reactive metals such as lithium, sodium and calcium to give corresponding hydrides in which the oxidation state of hydrogen is -1.
2 Li + H2 → 2 LiH
2 Na + H2 → 2 NaH
These hydrides are used as reducing agents in synthetic organic chemistry. It is used to prepare other important hydrides such as lithium aluminium hydride and sodium boro hydride.
4 LiH + AlCl3 → Li[AlH4] + 3 LiCl
4 NaH + B(OCH3)3 → Na[BH4] + 3 CH3ONa
Hydrogen itself acts as a reducing agent. In the presence of finely divided nickel, it adds to the unsaturated organic compounds to form saturated compounds.
HC=CH - -- Ni / H 2 → H 2 C = CH 2 - - Ni /H2 → H 3 C - CH3
Like hydrogen, deuterium also reacts with oxygen to form deuterium oxide called heavy water. It also reacts with halogen to give corresponding halides.
2 D2 + O2 → 2 D2O
D2 + X2 → 2 DX
(X = F, Cl, Br & I)
Deuterium can replace reversibly hydrogen in compounds either partially or completely depending upon the reaction conditions. These reactions occur in the presence of deuterium or heavy water.
CH4 + 2 D2 → CD4 + 2 H2
2 NH3 + 3 D2 → 2 ND3 + 3 H2
It is a β-emitter with a half-life period of 12.3 years .
13 T → 32 He +10 e