Hello everyone, I have a small question regarding mass and volume flow rates. It is shown in my book that there is a difference between path functions and point functions. I can understand why work or heat for example are path functions. However, I don't understand why mass transfer is also a path function. Specifically, the following equation is my problem: -------------- δ[PLAIN]http://upload.wikimedia.org/math/2/0/5/2056619d3cf80e2d000509b6110c57ec.png= [Broken] ρV(normal)dA ----- They followed by discussing that for a given radius, the Area is known but is not the case for the integral of δm and we cannot say [PLAIN]http://upload.wikimedia.org/math/2/0/5/2056619d3cf80e2d000509b6110c57ec.png2- [Broken] [PLAIN]http://upload.wikimedia.org/math/2/0/5/2056619d3cf80e2d000509b6110c57ec.png1... [Broken] I want to understand why is it so. We can clearly define the mass flow at a particular position. Can't we? Thanks to whoever contributes.