A quantity of n moles of an ideal gas (constant pressure molar heat capacity c_p
ID: 1599095 • Letter: A
Question
A quantity of n moles of an ideal gas (constant pressure molar heat capacity c_p) is initially at pressure p_o and temperature T_o. The gas the contracts isothermally to half the initial volume, then expands isobarically back to the initial volume, and finally returns isochorically to the initial state. a) What is the initial volume of the gas? b) Calculate the work done by the gas during the isothermal contraction. c) Calculate the change in entropy of the gas during the isothermal contraction. d) Calculate the efficiency of an engine that uses the described cycle. Write your results only in terms of n, p_o, T_o, and c_p.Explanation / Answer
a) pv0 = nRt0
vo = nRT0/P0
b) w = -nRT0ln(v0/2v0) = 0.693nRT0
c) change in entropy = Q/T
Q = -W
CHANGE IN ENTORPY = -0.693nR
D) efficinecy = 1-QOUT/QIN