A balloon is flat, and may be assumed to contain no air. It is then connected via a valve toa tank of air at 300 C (573.15 K) and at a certain pressure above atmospheric pressure. The valve is opened and air flows slowly into the balloon until the pressure reaches the same pressure as in the tank; then the valve is closed. Determine the final temperature of air in the balloon. (Hint: the internal energy and the enthalpy of air may be treated as functions of temperature only. Neglect the work done by the balloon.)