Problem Set #5

Example 4.2 Specific Enthalpy Change in Air
Air is sparged into a bioreactor at room temperature (25 C) and heated up to 37 C. The air is
allowed to expand during the heating such that the bioreactor maintains a constant pressure at
1.0 atm. Given that the specific internal energy of air increases by approximately 250 J/mol as
air is warmed, what is the difference in specific enthalpy of air between these two states? The
molecular weight of air is approximately 28.9 g/mol. Assume the air behaves as an ideal gas.
Example 4.3 Expansion of a Gas
A container with a gas and a movable piston contains a gas-phase reaction that produces 61.3J
of heat. The total number of moles of gas in the system does not change. The gas inside the
container has an initial volume of 1.0L at 298 K and 1atm. If the temperature rises to 350K and
pressure from the piston remains constant, what will be the volume of the gas be? How much
work is done on the system when the gas expands? What is the change in internal energy of the
gas? Assume that the gas behaves like an ideal gas.
Example 3
Given the following information about a system, calculate specific enthalpy (in Btu/lbm).
P=100 psia V=1.6 ft3/lbm U = 600 Btu/Lbm Note: 778 ft-lbf=1 Btu
Example 4
A 5 lbm system was taken from 50° F to 150° F. How much energy in the form of heat was
added to the system to produce this temperature increase? Cp= 1.6 Btu/Lbm-F