Question

Why do boiling points increase as the molecules gets longer/bigger?

Answer 1

longer chains of molecules or bigger molecules in general have higher molecular mass so it takes more energy to accelerate the molecules from liquid 2 gas phase. so the bp increases

Answer 2

boiling point increases as molecular mass increases - Larger molecules has stronger forces between them which cause their hike in boiling points.The intermolecular forces at work are van der Waals forces. These van der Waals forces are greater when the molecules are bigger.