4 Due 2/26

1. Determine whether the ideal gas approximation is reasonable for the following conditions. State why or why not.
   1. Oxygen at 30$^\circ$C, 3 MPa
   2. Methane at 30$^\circ$C, 3 MPa
   3. Water at 30$^\circ$C, 3 MPa
   4. R-134a at 30$^\circ$C, 3 MPa
   5. R-134a at 30$^\circ$C, 100 kPa

2. A rigid tank holds 4 m$^3$ of air at 6 bar and 100$^\circ$C. To cool it down a bit, 2 kg of air is allowed to escape. This lowers the temperature by 25$^\circ$C. What is the final pressure?

3. In the ideal Diesel cycle, the combustion proceeds isobarically. Assume that the air-fuel mixture can be approximated as plain air, and that the initial volume is 0.5 L and the final volume 1.3 L, while the initial pressure and temperature are 7 MPa and 700$^\circ$C. What is the mass of the air, and the final temperature in degrees centrigrade?

4. (Refer to figure P3.73 / P 3.53 in the book.) A rigid tank $A$ of volume 2 m$^3$ is connected by a valve to another tank $B$ with twice the volume. Tank $A$ holds nitrogen at 100 kPa and 250 K, tank $B$ nitrogen at 200 kPa and 300 K. The valve is opened and the combined tanks come to a uniform state at a temperature of 280 K. What is the pressure in the tanks then?