Hydrogen
4.0 Physical Properties
4.0 Physical Properties
1. It is colourless, odourless, tasteless and highly combustible gas.
2. Dihydrogen $H_2$ exists in two different forms known as ortho form and para form. Two hydrogen nuclei in ortho form have parallel spin while that of para hydrogen have opposite spin.
Due to the difference in nuclear spin ortho and para hydrogens have different physical properties (eg. boiling point, specific heats, thermal conductivity etc.). Para form has low internal energy and hence at absolute zero a sample of hydrogen gas only contains para form. At higher temperature percentage of ortho form increases.
