Hi all, This is my first post since I'm unable to find the answer myself & on the net too. My query is lets consider we have 3 types of system 1. Air tank at 10 bar pressure. It will have105*10*1= 1000 KJ energy. 2. Water tank of volume 1 cum and height of 1 m. It will have 5.04*h2 = 5.04 KJ (h= water head pressure) 3. Now lets say we have 2 cum of volume containing water of 1 cum and 1 cum air at 10 bar. can I say we have energy in water= 5.01*1002 = 50400 KJ (10 bar=100 m of water) plus when water is out of tank volume of air will be 2 cum at 5 bar. then energy stored in air (considering isothermal expansion)= 500 KJ so total 50900 KJ. Am I doing wrong some where/ everywhere then where is it wrong? If not why there is so diffrence in energy?