Gas expansion

Hey - I'm doing this question (see below) but I dont hav a clue where to start!!!

A flask with a volume of V, provided with a stopcock, contains ethane gas 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.

What is the final pressure of the ethane in the flask?

and

How many grams of ethane remain in the flask? Use R for the ideal gas constant.

for the first part i tried relating the initial and final pressures and volumes as a ratio... but that didn't work and since I dont have the volume of the actual gas which changes I cant apply the pV=nCRT equation...
Can someone tell me how to start?

OlderDan
Homework Helper
WY said:
Hey - I'm doing this question (see below) but I dont hav a clue where to start!!!

A flask with a volume of V, provided with a stopcock, contains ethane gas 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.

What is the final pressure of the ethane in the flask?

and

How many grams of ethane remain in the flask? Use R for the ideal gas constant.

for the first part i tried relating the initial and final pressures and volumes as a ratio... but that didn't work and since I dont have the volume of the actual gas which changes I cant apply the pV=nCRT equation...
Can someone tell me how to start?