A tank of 0.35m^3 capacity contains H2 S gas at 300K. When 2.5 kg of gas is withdrawn, the temperature in the tank becomes 288K and the pressure 10.5 bar. Calculate the mass of gas initially kept in the tank and also the initial pressure.

Answer 1

At the end. P = 10.5 bar = 10.36 atm: V = 0.35 m^3 = 350 L: T = 288 K:
PV = nRT.
n = PV/RT = 10.36*350/0.08205*288
n = approx 150 but you need a better number than that.
grams H2S = 150 moles x molar mass H2S = 150*34 = approx 5,000 g. That's the mass of H2S in the tank AFTER 2.5 kg has been released. Therefore, the amount H2S initially is about 2,500 g + 5,000 = approx 7,500 g H2S.
What's the initial pressure? The conditions are as follows:
P = ?: V = 350 L: n = approx 7500/34 = approx 220 moles: T = 300 K
Plug into PV = nRT and solve for P (in atm). Convert to bar if needed knowing 1 bar = 0.987 atm. Remember that the calculations I've done are approximate and you should go through each one.Post your work if you run into trouble. BTW, this is not a thermodynamics problem (or if it is I've missed it badly). I think it is a idea gas problem. I spent quite some time trying to make it a Joule-Thomson (Lord Kelvin) problem.