Molecular Structure and Properties
Hydrazine forms a monohydrate that is more dense (1.032 g/cm3) than the anhydrous material.
Hydrazine can arise via coupling a pair of ammonia molecules by removal of one hydrogen per molecule. Each H2N-N subunit is pyramidal in shape. The N-N distance is 1.45 Å (145 pm), and the molecule adopts a gauche conformation. The rotational barrier is twice that of ethane. These structural properties resemble those of gaseous hydrogen peroxide, which adopts a "skewed" anticlinal conformation, and also experiences a strong rotational barrier.
Hydrazine has basic (alkali) chemical properties comparable to those of ammonia:
- N2H4 + H2O → + + OH−
with the values:
- Kb = 1.3 x 10−6
- pKa = 8.1
(for ammonia Kb = 1.78 x 10−5)
Hydrazine is difficult to diprotonate:
- + + H2O → 2+ + OH− Kb = 8.4 x 10−16
The heat of combustion of hydrazine in oxygen (air) is 194.1 x 105 J/kg (9345 BTU/lb).
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