1. The problem statement, all variables and given/known data Two thermally insulated vessels are connected by a narrow tube fitted with a valve that is initially closed. One vessel of volume 16.8 L contains oxygen at a temperature of 300 K and a pressure of 1.75 atm. The other vessel of volume 22.4 L contains oxygen at a temperature of 450 K and a pressure of 2.25 atm. When the valve is opened, the gases in the two vessels mix, and the temperature and pressure become uniform throughout. (a) What is the final temperature? (b) What is the final pressure? (Ans. (a) 380 K , (b) 2.06 x 105 Pa or 2.04 atm) 2. Relevant equations 3. The attempt at a solution The teacher used the method of heat in=heat out (m1)c(T-300)=(m2)c(450-T) and obtain T=380K I did it by Total Energy of system is conserved. For an ideal gas, U=KE 3/2(n1)R300+3/2(n2)R450=3/2(n1+n2)RT T=380K Is the method i used correct? And how come the teachers method is correct? The pressure is different in the vessels. So shouldn't that be taken into account?