1. duften and riechen
duften is only used for scents that smell good (the meaning of this word actually has a strong emphasis on "smelling VERY GOOD"). flowers, fragrances, parfume, good meals etc. The cannotation is positive.
riechen just means "smelling". it's used to describe all kinds of scents, good, bad or weired smelling ones. riechen itself is neutral. It's like saying "it smells". Now what? How does it smell? Good, bad, funny. RIECHEN just describes that you've noticed a certain smell. You additionally need an adjective to make it clear.
2. satt and voll
if you decribe the state of not being hungry
SATT= not being hungry anymore (is also used in certain phrasal verbs) is a little - just a little - bit more formal compared to voll.
VOLL= literal meaning: full.
3. abspuelen and waschen
abspülenl iteral= to swill
abspülen or better spülen colloquial = washing the dishes.
waschen= to wash (cloth, your car, etc).
BTW: washing the dishes = Geschirr spülen or Geschirr abspülen. Here may be a slight difference though. The first describes the whole act (from start to finish = washing the dishes). The meaning of the second one focuses more on the act of cleaning or rinsing a surface (in this case dishes). U can use both, but if you know the difference, of course use the first.
4. fertig and bereit
1st means "finished" second "ready"
5. leihen and ausleihen
lend and borrow
6. fern and weit
far and wide
7. spaet and verspaetet
late (as in "hurry up, it's late") and the second (delayed and being late.
8. sitzen and sich hinsetzen
sitting and to sit down