phy chem

Flask A : the flask that is immersed in a hot bath of 127°C.
Flask B : the flask that is kept at 27°C.

Let P be the final pressure, and n be the final number of moles of H2in flask A.

Flask A :
P1 = 0.5 atm, T1 = 273 + 27 = 300 K, n1 = 0.7mol
P2 = P, T2 = 273 + 127 = 400 K, n2 = n mol

PV = nRT, where V and R are constant.
nT/P = V/R = constant
Then, n1T1/P1 = n2T2/P2
0.7 x 300 / 0.5 = n x 400 / P
P = 20n/21 ...... [1]

Flask B :
P1 = 0.5 atm, n1 = 0.7 mol
P2 = P, n2 = (0.7x2 - n) = (1.4 - n) mol

PV = nRT, where V, T and R are constant.
Then, P/n = RT/V = constant
P1/n­1 = P2/n2
0.5/0.7 = P/(1.4 - n)
P = (7 - 5n)/7 ...... [2]

[1] = [2] :
20n/21 = (7 - 5n)/7
20n/3 = 7 - 5n
20n = 21 - 15n
35n = 21
n = 0.6 (mol)
1.4 - n = 0.8 (mol)

Put n = 0.6 into [1] :
P = 20 x 0.6/21 = 4/7 atm = 0.571 atm

Final pressure in both flasks = 4/7 atm = 0.571 atm
No. of moles of H2 in the flask immersed in a hot bath at 127°C = 0.6 mol
No. of moles of H2 in the flask kept at 27°C = 0.8 mol