This is quite possibly very basic, but I have a horrible habit of forgetting basics as I move up the ladder in difficulty during the semester. This is a question regarding Thermodynamics, taken from Chapter 1; Introduction and the First Law of Thermodynamics of the book Applied Thermodynamics for Engineering Technologist (5th Edition). I am including the whole question just to avoid any misunderstandings. 1. The problem statement, all variables and given/known data A fluid at 0.7 bar occupying 0.09m3 is compressed reversibly to a pressure of 3.5 bar according to law pvn = constant. The fluid is then heated reversibly at constant volume until the pressure is 4 bar; the spesific volume is then 0.05m3 / kg. A reversible expansion according to a law pv2 = constant restores the fluid to its initial state. Sketch the cycle to a p-v diagram and calculate: i) The mass of fluid present (THIS is the one I cannot seem to figure out.. basics be damned) ii) the value of n in the first process. iii) the net work of the cycle. 2. Relevant equations It is a fluid, not explicitly stated to be gas or liquid, so the basic pv = nRT doesn't necessarily apply here. 3. The attempt at a solution I'm stumped, really. I have the answer (0.0753 kg) but I cannot figure out how to get to it.