Hello all, I am reading through Stephen Turns' An Introduction to Combustion. The third chapter is essentially a crash course on mass transport. In it, he talks about "the Stefan Problem" as it pertains to diffusion and Fick's Laws. I am understanding most of it, but I am realizing that I had really never given much thought to the phenomenon of evaporation. I am not really sure that I understand why it occurs? Clearly, water can evaporate away without reaching it's boiling point. So there a difference between evaporation and vaporization (right?). If I am understanding the text, than it seems that if we place a liquid, denoted Liquid A, in a graduated cylinder, then at the liquid-air interface, there will exist some gaseous A. I am just not clear of the mechanism that causes this gaseous A to exist? Any thoughts on this?