Ethane is an alkane and as such is saturated, Ethene is an alkene and as such is unsaturated.
Chemicaly we can identify by adding bromine water to both alkane and alkene. In which ever cause colour changes that compound is ethene (alkene).
Ethane : CH₃ – CH₃
Ethene : CH₂ =CH₂
CH₃ – CH₃ + Br₂ → no reaction: no colour change
CH₂ =CH₂ + Br₂ → CH₂(Br) – CH₂(Br): colour change