Chapter 6
Chapter 6
Chapter 6
Estimate the change in enthalpy and entropy when liquid ammonia at 270 K is compressed
from its saturation pressure of 381 kPa to 1,200 kPa. For saturated liquid ammonia at 270 K,
Vl = 1.551 x 10-3 m3 kg -1, and β= 2.095 x 10-3 K-1 .
6.8. Liquid isobutane is throttled through a valve from an initial state of 360 K and 4,000 kPa to
a final pressure of 2,000 kPa. Estimate the temperature change and the entropy change of
isobutane. The specific heat of liquid isobutane at 360 K is 2.78 J g -1 oC-1. Estimates of V and
β may be found from Eq. (3.72).
6.9. One kilogram of water (V1 = 1,003 cm3 kg-1 ) in a piston/cylinder device at 25 oC and 1 bar is
compressed in a mechanically reversible, isothermal process to 1,500 bar. Determine Q, W,
∆U, ∆H, and ∆S given that β = 250 x 10-6 K-1 and κ = 45 x 10-6 bar -1. A satisfactory
assumption is that V is constant at its arithmetic average value.
6.10. Liquid water at 25oC and 1 bar fills a rigid vessel. If heat is added to the water until its
temperature reaches 50oC, what pressure is developed? The average value of β between
25 and 50oC is 4.42 x 10-5 bar-1, and may be assumed independent of P. The specific
volume of liquid water at 25oC is 1.0030cm3 g-1.
6.17. Estimate the entropy change of vaporization of benzene at 50oC. The vapor pressure of
benzene is given by the equation:
lnPsat 2,788.51
=13.8858−
kPa t
+ 220.79
℃