I'm doing a class on thermodynamics and energy and well there's this chapter about pure substances and subcooled liquids, saturated liquids, superheated, etc. stuff like that.
The chapter begins by showing a piston-cylinder in an initial state containing liquid water and a mass is kept on top of it to keep the pressure constant. Thats what I don't understand, how can a mass on top of the piston keep the pressure constant?, I mean first of all as the water is heated should the volume not increase(as gas) by the PV=mRT, and since volume is proportional to pressure it should increase too?
Can someone explain how the fixed mass on top of the piston-cylinder device keeps pressure constant as the water is heating through several phases.
The Attempt at a Solution