Chemical properties of hydrogen H2
Combustion
Hydrogen gas is highly flammable and will burn in air at a very wide range of concentrations between 4% and 75% by volume. The enthalpy of combustion for hydrogen is -286 kJ/mol.
- 2H2(g) + O2(g) 2H2O(l) + 572 kJ (286 kJ/mol)
Reaction with nitrogen
Reaction with nitrogen at high pressure and temperature produces ammonia(NH3). This is the method for the production of ammonia by Haber process. The enthalpy hydrogen ΔH is -92.6 kJ/mol.
- N2(g) + 3H2(g) 2NH3(g) + 572 kJ (286 kJ/mol)
Reaction with oxigen/Oxidation
Reaction with oxigen produces water. The enthalpy of oxidation for hydrogen is -286 kJ/mol.
- 2H2(g) + O2(g) 2H2O(l)
Reaction with metals
Hydrogen combines with many metals like Na, K, Ca, Li to form metal hydrides.
- Ca + H2 CaH2
Metals like Pt, Pd, Ni form interstitial hydrides by absorbing large volume of hydrogen. Such hydrogen is called occluded hydrogen.
Reaction with metal oxides
Hydrogen reduces oxides of less active metals to corresponding metals.
- CuO + H2 Cu + H2
Reaction with halogens
Hydrogen combines readily with the halogens which include fluorine, chlorine, bromine, iodine, and astatine to form halides.
- Cl2(g) + H2(g) 2HCl(g)