Calculate the standard enthalpy difference between 2-ethyl-1-butene and 1-hexene to determine which molecule is more stable. The heats of formation are -55.8 kJ/mol for 2-ethyl-1-butene and -40.5 kJ/mol for 1-hexene.
2-ethyl-1-butene is more stable by 15.3 kJ/mol.
The two stabilities can't be compared because the molecules are not isomers. 1-Hexene is more stable by 15.3 kJ/mol.