4 Due 1/20

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 constant pressure cylinder/piston configuration holds 2m$^3$ of air at 5$^\circ$C and standard atmospheric pressure. What is the mass of the air? If the air is now cooled until the volume is half the original one, then what is the final temperature of the air in degrees centrigrade?

3. 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?

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?