I. Di i on mechan i sms 1. Direct exchange of neighboring atoms Atom must acquire additional energy ag called the activation energy, before they jump from normal state to activated state(the saddle point) △G"=△H-TAS=△E+P△V*-TAS* This mechanism seems to be unrealistic for large Ag◆ Ⅱ.Diffusion Mechanisms 1. Direct exchange of neighboring atoms. Atom must acquire additional energy ,called the activation energy, before they jump from normal state to activated state (the saddle point). This mechanism seems to be unrealistic for large  G  G       G = H −TS = E + PV −TS