Hi, new forumer here. I've found this site a couple times before from google searches and whatnot but I've always been too scared to post here as everyone seems much too intelligent for my questions. However I can't find a decent answer to this question, perhaps there isn't one, however I remain hopeful! Anyway, enough chitchat. What is enthalpy? I get that h = u + Pv but when you're calculating heat added in a boiler or work done in a turbine it's always H2-H1 which leads me to believe it's the internal energy of the gas/vapour. But then that's U. So I'm confused as to what enthalpy actually IS Cheers please don't flame too hard, I'm only a second year undergraduate! edit: my english skill is...well... lacking.