Mar 16, 2010
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So work is -pextdv right? or is w=d(pv)? im really confused as to which of the two it is... and then what is vdp in dh=du + d(vp)? also if someone knows what is the difference between dh and du? something about dh taking into account the external energy or something? i forgot...

Thanks
 

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So work is -pextdv right? or is w=d(pv)? im really confused as to which of the two it is... and then what is vdp in dh=du + d(vp)? also if someone knows what is the difference between dh and du? something about dh taking into account the external energy or something? i forgot...

Thanks
For the systems that show up on the MCAT (at least the ones that have so far), you can consider work to be Wby system = PextdV. Most questions along these lines involve an application of the Carnot cycle (simplistic heat engine or heat pump), so distinguishing dH from dU is beyond the scope of the MCAT. As long as you know that there is heat energy versus total internal energy of the system, you are at or beyond the level of what you need for the MCAT.