What is the work to compress a gas under constant external pressure? It seems that it is supposed to be w = -P(ext)delta(V) This equation is certainly true for expansion of a gas, is it also true for compression? So if we have two gases, same initial conditions, same delta(v) under compression. One is compressed by 10 atm and the other by 5 atm. They end at the same volume, but have different work done on them? The observational difference I can see is that the 10 atm compression would occur faster than the 5 atm compression. Is the work really a factor of 2 different? Or, is work really dependent upon the lower of internal and external pressures, and the books talk about expansion more than compression?