in my hand- exchange, magical dimensionand serial spell.

i play exchange and then activate serial spell straight after as it is quick play. serial spell allows me to discard every card in my hand to duplicate i magic card i just played. does this mean i can activate exchange, play serial spell and then my opponent gets nothing from me and i get any card i want from his hand?

I don't think so. In order for Exchange to resolve properly, both players need at least 1 card in their hand, so if either player has no card when Exchange resolves, then it resolves without effect. So both your Serial Spell and your Exchange wouldn't do anything.

ye but if i activate exchange and then serial spell from my hand, which effect activates first....this part of the game i dont understand. and can a quick play spell card be played from your hand in an opponents turn or does it have to be set face down like traps and then activated in your opponents turn?

Serial Spell will resolve it's effect first (since the chain resolves in reverse order) but since Serial Spell is copying the effect of Exchange, the rule still applies that you have to have a card to exchange with your opponent in order for the effect to resolve.

I hope this helps.

my devious plan is foiled again! damn!

To answer the other part of your question, Quick-Play Spell cards can be activated from your hand during any phase of your own turn, but must be Set on the field in order to be activated during your opponent's turn.