7.18. A horizontal cylinder equipped with a frictionless piston contains 785 cm' of steam at 400 K and 125 kPa. A total of 83.8 joules of heat is transferred to the steam, causing the steam temperature to rise and the cylinder volume to increase. A constant restraining force is maintained on the piston throughout the expansion, so that the pressure exerted by the piston on the steam remains constant at 125 kPa.
7.18. A horizontal cylinder equipped with a frictionless piston contains 785 cm' of steam at 400 K and 125 kPa. A total of 83.8 joules of heat is transferred to the steam, causing the steam temperature to rise and the cylinder volume to increase. A constant restraining force is maintained on the piston throughout the expansion, so that the pressure exerted by the piston on the steam remains constant at 125 kPa.
Introduction to Chemical Engineering Thermodynamics
8th Edition
ISBN:9781259696527
Author:J.M. Smith Termodinamica en ingenieria quimica, Hendrick C Van Ness, Michael Abbott, Mark Swihart
Publisher:J.M. Smith Termodinamica en ingenieria quimica, Hendrick C Van Ness, Michael Abbott, Mark Swihart
Chapter1: Introduction
Section: Chapter Questions
Problem 1.1P
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Transcribed Image Text:7.18. A horizontal cylinder equipped with a frictionless piston contains 785 cm³ of steam at 400 K and
125 kPa. A total of 83.8 joules of heat is transferred to the steam, causing the steam temperature to
rise and the cylinder volume to increase. A constant restraining force is maintained on the piston
throughout the expansion, so that the pressure exerted by the piston on the steam remains constant
at 125 kPa.
Energy and Energy Balances
Steam
Steam
P = 125 kPa
T = 400 K
V = 785 cm3
P = 125 kPa
T = ?
V = ?
Q = 83.8 J
The specific enthalpy of steam at 125 kPa varies with temperature approximately as
Ĥ(J/mol)
= 34,980 + 35.5T(K)
(a) Taking the steam as the system, convince yourself that Q = AH for this process-that is, the four
conditions specified in Part (a) of Problem 7.17 are applicable. Then prove that the final steam
temperature is 480 K. Finally, calculate (i) the final cylinder volume, (ii) the expansion work done
by the steam, and (iii) AU(J).
(b) Which of the specified conditions of Problem 7.17 would have been only an approximation if the
cylinder were not horizontal?
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