· 5.19 use the relationship between the pressure and volume of a fixed mass of gas at constant temperature: p1V1 = p2V2 p1 = Pressure at the beginning [kPa, bar or atm] V1 = Volume at the beginning [m3 or cm3] p2 = Pressure at the end [kPa, bar or atm] V2 = Volume at the end [m3 or cm3] (Note: can use any units for V and p as long as they are the same at the beginning and end)