G.16.1- A spell or ability may instruct players to exchange something. For example, life totals or control of two permanents. [CompRules 1999/04/23]
G.16.2- The exchange effect fails to do anything if any part of the exchange cannot take place. For example, if a spell attempts to exchange control of two target creatures but one of them is destroyed before it resolves, the spell does nothing. [CompRules 1999/04/23]
G.16.3- When life totals are exchanged, each player gains or loses the amount of life necessary to equal the other player's previous life total. Replacement effects may modify these gains and losses and triggered abilities may trigger on them. [CompRules 1999/04/23]
G.16.4- An exchange with a card in the graveyard puts the card that was in play into its owner's graveyard, regardless of whose graveyard the card is taken out of. [WotC Rules Team 1999/03/18] See Goblin Welder. And the card goes on top of the graveyard, not into the middle of it. [bethmo 1999/03/21]