Two Tanks, Both of Volume 10 L, Are Connected by a Valve

Multiple Choice

Two tanks, both of volume 10 L, are connected by a valve and are thermally isolated. One tank contains 1mole of ⁴He at 280 K and the other tank contains 1 mole O₂ at 300 K. The valve is then opened and the gases allowed to mix. What is the final temperature after the gases have come to equilibrium?

A) 290 K
B) 295 K
C) 285 K
D) 293 K
E) 287 K