A piston-and-cylinder device contains 10 kmols of n-pentane at 35.5C and 100 bar. Slowly the piston is

Question:

A piston-and-cylinder device contains 10 kmols of n-pentane at −35.5°C and 100 bar. Slowly the piston is moved until the vapor pressure of n-pentane is reached, and then further moved until 5 kmols of the n-pentane is evaporated. This complete process takes place at the constant temperature of −35.5°C. Assume n-pentane can be described by the van der Waals equation of state. The following data are available from the vdW equation state at −35.5°C

Pvap = 1.013 bar Z(liquid) = 0.009077 P = 100 bar Z(liquid) 0.69075 = Z(vapor) = 0.94016