Question

which conformation of Ethane is more stable

Answer 1

The hydrogen atoms have a dihedral angle of 0º. The staggered conformation of ethane is more stable than the eclipsed form by 12.1 kJ/mol, so that as one methyl group rotates 360º relative to the other, the compound passes through three stable staggered conformers via three unstable eclipsed forms.

Answer 2

In the staggered conformation, the hydrogen atoms are lined up to be equally spaced apart in the newman projection. For the eclipsed conformation, each hydrogen on the front carbon overlaps with the hydrogens on the back carbon. In terms of stability, the staggered conformation is more stable than the eclipses.