Question

wo lbs of water vapor in a piston-cylinder assembly expands at a constant pressure of 250 lbf/in2 from a saturated vapor state to a volume of 7.08 ft3. Determine the initial and final temperatures, in °F, and the work for the process, in Btu.

Answer 1

To determine the initial and final temperatures and the work for the process, we need to use the ideal gas law and the first law of thermodynamics. The initial and final temperatures can be calculated using the ideal gas law and the work can be determined using the first law of thermodynamics.

Step-by-step explanation:

In order to determine the initial and final temperatures and the work for the process, we need to use the ideal gas law and the first law of thermodynamics. The ideal gas law states that PV = nRT, where P is the pressure, V is the volume, n is the number of moles, R is the gas constant, and T is the temperature. The first law of thermodynamics states that the change in internal energy of a system is equal to the heat added to the system minus the work done by the system.

Using the given information, we can calculate the initial and final temperatures by rearranging the ideal gas law equation and solving for T:

T1 = (P1V1)/(nR) and T2 = (P2V2)/(nR).

Once we have the initial and final temperatures, we can calculate the work for the process using the first law of thermodynamics equation:

W = ΔU + Q.

Since the process is occurring at constant pressure, the equation becomes:

W = ΔU + PΔV.

Here, ΔU represents the change in internal energy, which is equal to the final internal energy minus the initial internal energy. We can use the ideal gas law to calculate the initial and final internal energies:

U1 = (nRT1)/(y-1) and U2 = (nRT2)/(y-1).

Finally, we can substitute the values into the equation for work and calculate the result. The units of work will be in Btu.