2013-3-6 eReview:Energy Balance for a Closed System Review:Closed Sys.Energy Balance The energy concepts introduced thus far are summarized in words as follows: change in the amount net amount of energy net amount of energy of energy contained trans rred in acros the time interval time interval Using previously defined symbols,this can be expressed as:E2-E1=Q-W Alternatively,△KE+△PE+△U=Q-W Be aware of the signs!A minus sign appears before w because energy transfer by work from the system to the surrounding is taken as positive 4-18 9 2013-3-6 9 Review: Energy Balance for a Closed System http://bcs.wiley.com/he-bcs/Books?action=index&itemId=0470918012&bcsId=6606 ►The energy concepts introduced thus far are summarized in words as follows: change in the amount of energy contained within a system during some time interval net amount of energy transferred in across the system boundary by heat transfer during the time interval net amount of energy transferred out across the system boundary by work during the time interval ►Using previously defined symbols, this can be expressed as: E2 – E1 = Q – W ►Alternatively, ΔKE + ΔPE + ΔU = Q – W Be aware of the signs! A minus sign appears before W because energy transfer by work from the system to the surrounding is taken as positive. 4-18 Review: Closed Sys. Energy Balance