I'm really struggling with this concept and can't seem to get my head around it. I don't know why because it seems simple enough but I can't seem to get the answer : Question: A flask with a volume 'V', provided with a stopcock, contains ethane gas (C2H6) at a temperature of T_0 and atmospheric pressure p_0. The molar mass of ethane is M. The system is warmed to a temperature of T, with the stopcock open to the atmosphere. The stopcock is then closed and the flask cooled to its original temperature. a) What is the final pressure of ethane in the flask? b) How many grams of ethane remain in the flask (use 'R' for ideal gas constant)?