Isomerism

The energy difference between the staggered and eclipsed conformation of ethane is $12.55 \mathrm{~kJ} / \mathrm{mol}$

Staggered conformation of ethane is more stable than the eclipsed conformation.

The distance between non-bonded H -atoms of ethane in eclipsed conformation is $2.29\($\mathop A\limits^o\)

A $90^{\circ}$ rotation converts staggered conformation of ethane into eclipsed conformation.