Problem 9.7: A reservoir contains natural gas at a pressure of 5000 psig and a temperature of 180 °F. The composition of the gas is 80% methane, 15% ethane, and 5% CO2 (all fractions are by mole). Estimate the temperature of the gas when it emerges at the surface under the following alternative assumptions:

a) The flow to the surface is assumed to be reversible adiabatic expansion.

b) The flow to the surface is assumed to be a throttling process.

Take the natural gas to be an ideal-gas mixture with temperature-dependent heat capacities for each component given in Perry's Handbook. Is the ideal-gas assumption reasonable?