Question

Why question3 is P

Use of Tabulated Enthalpy Data The following entries are taken from a data table for saturated methyl chloride: TCF P(psia) V(ft /lb H(Btu/lbm) State Liquid -40 6.878 0.01553 0 18.90 4.969 50 51.99 0.000 196.23 Vapor Vapor 202.28 1.920 1. What reference state was used to generate the given enthalpies? culate Afi and AU for the transition of saturated methyl chloride vapor from 50°F to O'F 3. What assum enthalpy? 1. Liquid at Part 2 40°F and 6.878 psia (the state at which H = 0) You do not need this information to solve on 2. AH H(O'F) H(50F) (196.23 202.28)6.05 Btu/b =-6.05 Btu/lbm (18.90)(4.969) -(51.99)(1.920)] ft psia/lb 1.987 Bu 10.73 ft psia The value of the conversion factor Btu/(ft psia) was obtained from the table of gas constants in back of the book. (Verify it!) 4.96 Btu/lbm 3. H was assumed independent of P.

Why H was independent of P

Answer 1

At moderate pressures, most gases behave as ideal gases and hence their enthalpy is independent of pressure and a function of temperature only. At higher pressures, even though enthalpy depends on pressure, its effect is negligible in comparision to the effect of temperature.