A gas has CP* = 5R and is described by the following equation of state:
?V=RT/P+ aTP
where a = 0.150 m3/mol•Pa•K. Determine the change in molar internal energy when this gas is expanded from 750 K and 2 MPa to 350 K and 50 kPa.
A.-13.3 kJ/mol
B.5.45 kJ/mol
C.31.7 kJ/mol
D.-45 kJ/mol
E.Insufficient information to solve
A. Incorrect. The residual properties are important and cannot be ignored here.
B. Incorrect. You are making an error with your units; one term is three orders of magnitude less than you have counted it as.
C. Correct. This may seem incorrect because of the positive sign accompanying a temperature drop, but if the gas really follows this EOS, the residual in this case is larger in magnitude than the ideal gas contribution to the change in molar internal energy.
D. Incorrect. This is the value of one of the residual properties, but we must account for both residual properties and the ideal gas change in molar internal energy.
E. Incorrect. This problem CAN be solved with the information given.
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