A vessel of volume 0.2 m^3 contains nitrogen gas at 1.013 bar and 15 celcius. If 0.2 kg of nitrogen is now pumped into the vessel, calculate the new pressure when the vessel has returned to its initial temperature. The molecular weight of nitrogen is 28, and it may be assumed that the gas is a perfect gas. The universal gas constant is 8.314 kNm / kmoleK I solve it in this way: PV = nRT P= nRT / V = 200/28 x 8.314 x 288 x 1 / 0.2 = 85515 Pa = 0.855bar New pressure = 0.855bar + 1.013 bar = 1.87 bar The answer I get is same with the given correct answer. However, my lecturer told me that my solution is wrong even I got my final answer correctly. Can anyone explain to me what`s the reason? Thanks in advance.